text: /*
   *  linux/fs/namei.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   */
  
  /*
   * Some corrections by tytso.
   */
  
  /* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname
   * lookup logic.
   */
  /* [Feb-Apr 2000, AV] Rewrite to the new namespace architecture.
   */
  
  #include <linux/init.h>
  #include <linux/export.h>
  #include <linux/kernel.h>
  #include <linux/slab.h>
  #include <linux/fs.h>
  #include <linux/namei.h>
  #include <linux/pagemap.h>
  #include <linux/fsnotify.h>
  #include <linux/personality.h>
  #include <linux/security.h>
  #include <linux/ima.h>
  #include <linux/syscalls.h>
  #include <linux/mount.h>
  #include <linux/audit.h>
  #include <linux/capability.h>
  #include <linux/file.h>
  #include <linux/fcntl.h>
  #include <linux/device_cgroup.h>
  #include <linux/fs_struct.h>
  #include <linux/posix_acl.h>
  #include <linux/hash.h>
  #include <asm/uaccess.h>
  
  #include "internal.h"
  #include "mount.h"
  
  /* [Feb-1997 T. Schoebel-Theuer]
   * Fundamental changes in the pathname lookup mechanisms (namei)
   * were necessary because of omirr.  The reason is that omirr needs
   * to know the _real_ pathname, not the user-supplied one, in case
   * of symlinks (and also when transname replacements occur).
   *
   * The new code replaces the old recursive symlink resolution with
   * an iterative one (in case of non-nested symlink chains).  It does
   * this with calls to <fs>_follow_link().
   * As a side effect, dir_namei(), _namei() and follow_link() are now 
   * replaced with a single function lookup_dentry() that can handle all 
   * the special cases of the former code.
   *
   * With the new dcache, the pathname is stored at each inode, at least as
   * long as the refcount of the inode is positive.  As a side effect, the
   * size of the dcache depends on the inode cache and thus is dynamic.
   *
   * [29-Apr-1998 C. Scott Ananian] Updated above description of symlink
   * resolution to correspond with current state of the code.
   *
   * Note that the symlink resolution is not *completely* iterative.
   * There is still a significant amount of tail- and mid- recursion in
   * the algorithm.  Also, note that <fs>_readlink() is not used in
   * lookup_dentry(): lookup_dentry() on the result of <fs>_readlink()
   * may return different results than <fs>_follow_link().  Many virtual
   * filesystems (including /proc) exhibit this behavior.
   */
  
  /* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation:
   * New symlink semantics: when open() is called with flags O_CREAT | O_EXCL
   * and the name already exists in form of a symlink, try to create the new
   * name indicated by the symlink. The old code always complained that the
   * name already exists, due to not following the symlink even if its target
   * is nonexistent.  The new semantics affects also mknod() and link() when
   * the name is a symlink pointing to a non-existent name.
   *
   * I don't know which semantics is the right one, since I have no access
   * to standards. But I found by trial that HP-UX 9.0 has the full "new"
   * semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the
   * "old" one. Personally, I think the new semantics is much more logical.
   * Note that "ln old new" where "new" is a symlink pointing to a non-existing
   * file does succeed in both HP-UX and SunOs, but not in Solaris
   * and in the old Linux semantics.
   */
  
  /* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink
   * semantics.  See the comments in "open_namei" and "do_link" below.
   *
   * [10-Sep-98 Alan Modra] Another symlink change.
   */
  
  /* [Feb-Apr 2000 AV] Complete rewrite. Rules for symlinks:
   *	inside the path - always follow.
   *	in the last component in creation/removal/renaming - never follow.
   *	if LOOKUP_FOLLOW passed - follow.
   *	if the pathname has trailing slashes - follow.
   *	otherwise - don't follow.
   * (applied in that order).
   *
   * [Jun 2000 AV] Inconsistent behaviour of open() in case if flags==O_CREAT
   * restored for 2.4. This is the last surviving part of old 4.2BSD bug.
   * During the 2.4 we need to fix the userland stuff depending on it -
   * hopefully we will be able to get rid of that wart in 2.5. So far only
   * XEmacs seems to be relying on it...
   */
  /*
   * [Sep 2001 AV] Single-semaphore locking scheme (kudos to David Holland)
   * implemented.  Let's see if raised priority of ->s_vfs_rename_mutex gives
   * any extra contention...
   */
  
  /* In order to reduce some races, while at the same time doing additional
   * checking and hopefully speeding things up, we copy filenames to the
   * kernel data space before using them..
   *
   * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
   * PATH_MAX includes the nul terminator --RR.
   */
  
  #define EMBEDDED_NAME_MAX	(PATH_MAX - offsetof(struct filename, iname))
  
  struct filename *
  getname_flags(const char __user *filename, int flags, int *empty)
  {
  	struct filename *result;
  	char *kname;
  	int len;
  
  	result = audit_reusename(filename);
  	if (result)
  		return result;
  
  	result = __getname();
  	if (unlikely(!result))
  		return ERR_PTR(-ENOMEM);
  
  	/*
  	 * First, try to embed the struct filename inside the names_cache
  	 * allocation
  	 */
  	kname = (char *)result->iname;
  	result->name = kname;
  
  	len = strncpy_from_user(kname, filename, EMBEDDED_NAME_MAX);
  	if (unlikely(len < 0)) {
  		__putname(result);
  		return ERR_PTR(len);
  	}
  
  	/*
  	 * Uh-oh. We have a name that's approaching PATH_MAX. Allocate a
  	 * separate struct filename so we can dedicate the entire
  	 * names_cache allocation for the pathname, and re-do the copy from
  	 * userland.
  	 */
  	if (unlikely(len == EMBEDDED_NAME_MAX)) {
  		const size_t size = offsetof(struct filename, iname[1]);
  		kname = (char *)result;
  
  		/*
  		 * size is chosen that way we to guarantee that
  		 * result->iname[0] is within the same object and that
  		 * kname can't be equal to result->iname, no matter what.
  		 */
  		result = kzalloc(size, GFP_KERNEL);
  		if (unlikely(!result)) {
  			__putname(kname);
  			return ERR_PTR(-ENOMEM);
  		}
  		result->name = kname;
  		len = strncpy_from_user(kname, filename, PATH_MAX);
  		if (unlikely(len < 0)) {
  			__putname(kname);
  			kfree(result);
  			return ERR_PTR(len);
  		}
  		if (unlikely(len == PATH_MAX)) {
  			__putname(kname);
  			kfree(result);
  			return ERR_PTR(-ENAMETOOLONG);
  		}
  	}
  
  	result->refcnt = 1;
  	/* The empty path is special. */
  	if (unlikely(!len)) {
  		if (empty)
  			*empty = 1;
  		if (!(flags & LOOKUP_EMPTY)) {
  			putname(result);
  			return ERR_PTR(-ENOENT);
  		}
  	}
  
  	result->uptr = filename;
  	result->aname = NULL;
  	audit_getname(result);
  	return result;
  }
  
  struct filename *
  getname(const char __user * filename)
  {
  	return getname_flags(filename, 0, NULL);
  }
  
  struct filename *
  getname_kernel(const char * filename)
  {
  	struct filename *result;
  	int len = strlen(filename) + 1;
  
  	result = __getname();
  	if (unlikely(!result))
  		return ERR_PTR(-ENOMEM);
  
  	if (len <= EMBEDDED_NAME_MAX) {
  		result->name = (char *)result->iname;
  	} else if (len <= PATH_MAX) {
  		struct filename *tmp;
  
  		tmp = kmalloc(sizeof(*tmp), GFP_KERNEL);
  		if (unlikely(!tmp)) {
  			__putname(result);
  			return ERR_PTR(-ENOMEM);
  		}
  		tmp->name = (char *)result;
  		result = tmp;
  	} else {
  		__putname(result);
  		return ERR_PTR(-ENAMETOOLONG);
  	}
  	memcpy((char *)result->name, filename, len);
  	result->uptr = NULL;
  	result->aname = NULL;
  	result->refcnt = 1;
  	audit_getname(result);
  
  	return result;
  }
  
  void putname(struct filename *name)
  {
  	BUG_ON(name->refcnt <= 0);
  
  	if (--name->refcnt > 0)
  		return;
  
  	if (name->name != name->iname) {
  		__putname(name->name);
  		kfree(name);
  	} else
  		__putname(name);
  }
  
  static int check_acl(struct inode *inode, int mask)
  {
  #ifdef CONFIG_FS_POSIX_ACL
  	struct posix_acl *acl;
  
  	if (mask & MAY_NOT_BLOCK) {
  		acl = get_cached_acl_rcu(inode, ACL_TYPE_ACCESS);
  	        if (!acl)
  	                return -EAGAIN;
  		/* no ->get_acl() calls in RCU mode... */
  		if (acl == ACL_NOT_CACHED)
  			return -ECHILD;
  	        return posix_acl_permission(inode, acl, mask & ~MAY_NOT_BLOCK);
  	}
  
  	acl = get_acl(inode, ACL_TYPE_ACCESS);
  	if (IS_ERR(acl))
  		return PTR_ERR(acl);
  	if (acl) {
  	        int error = posix_acl_permission(inode, acl, mask);
  	        posix_acl_release(acl);
  	        return error;
  	}
  #endif
  
  	return -EAGAIN;
  }
  
  /*
   * This does the basic permission checking
   */
  static int acl_permission_check(struct inode *inode, int mask)
  {
  	unsigned int mode = inode->i_mode;
  
  	if (likely(uid_eq(current_fsuid(), inode->i_uid)))
  		mode >>= 6;
  	else {
  		if (IS_POSIXACL(inode) && (mode & S_IRWXG)) {
  			int error = check_acl(inode, mask);
  			if (error != -EAGAIN)
  				return error;
  		}
  
  		if (in_group_p(inode->i_gid))
  			mode >>= 3;
  	}
  
  	/*
  	 * If the DACs are ok we don't need any capability check.
  	 */
  	if ((mask & ~mode & (MAY_READ | MAY_WRITE | MAY_EXEC)) == 0)
  		return 0;
  	return -EACCES;
  }
  
  /**
   * generic_permission -  check for access rights on a Posix-like filesystem
   * @inode:	inode to check access rights for
   * @mask:	right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC, ...)
   *
   * Used to check for read/write/execute permissions on a file.
   * We use "fsuid" for this, letting us set arbitrary permissions
   * for filesystem access without changing the "normal" uids which
   * are used for other things.
   *
   * generic_permission is rcu-walk aware. It returns -ECHILD in case an rcu-walk
   * request cannot be satisfied (eg. requires blocking or too much complexity).
   * It would then be called again in ref-walk mode.
   */
  int generic_permission(struct inode *inode, int mask)
  {
  	int ret;
  
  	/*
  	 * Do the basic permission checks.
  	 */
  	ret = acl_permission_check(inode, mask);
  	if (ret != -EACCES)
  		return ret;
  
  	if (S_ISDIR(inode->i_mode)) {
  		/* DACs are overridable for directories */
  		if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
  			return 0;
  		if (!(mask & MAY_WRITE))
  			if (capable_wrt_inode_uidgid(inode,
  						     CAP_DAC_READ_SEARCH))
  				return 0;
  		return -EACCES;
  	}
  	/*
  	 * Read/write DACs are always overridable.
  	 * Executable DACs are overridable when there is
  	 * at least one exec bit set.
  	 */
  	if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO))
  		if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE))
  			return 0;
  
  	/*
  	 * Searching includes executable on directories, else just read.
  	 */
  	mask &= MAY_READ | MAY_WRITE | MAY_EXEC;
  	if (mask == MAY_READ)
  		if (capable_wrt_inode_uidgid(inode, CAP_DAC_READ_SEARCH))
  			return 0;
  
  	return -EACCES;
  }
  EXPORT_SYMBOL(generic_permission);
  
  /*
   * We _really_ want to just do "generic_permission()" without
   * even looking at the inode->i_op values. So we keep a cache
   * flag in inode->i_opflags, that says "this has not special
   * permission function, use the fast case".
   */
  static inline int do_inode_permission(struct inode *inode, int mask)
  {
  	if (unlikely(!(inode->i_opflags & IOP_FASTPERM))) {
  		if (likely(inode->i_op->permission))
  			return inode->i_op->permission(inode, mask);
  
  		/* This gets set once for the inode lifetime */
  		spin_lock(&inode->i_lock);
  		inode->i_opflags |= IOP_FASTPERM;
  		spin_unlock(&inode->i_lock);
  	}
  	return generic_permission(inode, mask);
  }
  
  /**
   * __inode_permission - Check for access rights to a given inode
   * @inode: Inode to check permission on
   * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
   *
   * Check for read/write/execute permissions on an inode.
   *
   * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
   *
   * This does not check for a read-only file system.  You probably want
   * inode_permission().
   */
  int __inode_permission(struct inode *inode, int mask)
  {
  	int retval;
  
  	if (unlikely(mask & MAY_WRITE)) {
  		/*
  		 * Nobody gets write access to an immutable file.
  		 */
  		if (IS_IMMUTABLE(inode))
  			return -EACCES;
  	}
  
  	retval = do_inode_permission(inode, mask);
  	if (retval)
  		return retval;
  
  	retval = devcgroup_inode_permission(inode, mask);
  	if (retval)
  		return retval;
  
  	return security_inode_permission(inode, mask);
  }
  EXPORT_SYMBOL(__inode_permission);
  
  /**
   * sb_permission - Check superblock-level permissions
   * @sb: Superblock of inode to check permission on
   * @inode: Inode to check permission on
   * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
   *
   * Separate out file-system wide checks from inode-specific permission checks.
   */
  static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
  {
  	if (unlikely(mask & MAY_WRITE)) {
  		umode_t mode = inode->i_mode;
  
  		/* Nobody gets write access to a read-only fs. */
  		if ((sb->s_flags & MS_RDONLY) &&
  		    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
  			return -EROFS;
  	}
  	return 0;
  }
  
  /**
   * inode_permission - Check for access rights to a given inode
   * @inode: Inode to check permission on
   * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC)
   *
   * Check for read/write/execute permissions on an inode.  We use fs[ug]id for
   * this, letting us set arbitrary permissions for filesystem access without
   * changing the "normal" UIDs which are used for other things.
   *
   * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
   */
  int inode_permission(struct inode *inode, int mask)
  {
  	int retval;
  
  	retval = sb_permission(inode->i_sb, inode, mask);
  	if (retval)
  		return retval;
  	return __inode_permission(inode, mask);
  }
  EXPORT_SYMBOL(inode_permission);
  
  /**
   * path_get - get a reference to a path
   * @path: path to get the reference to
   *
   * Given a path increment the reference count to the dentry and the vfsmount.
   */
  void path_get(const struct path *path)
  {
  	mntget(path->mnt);
  	dget(path->dentry);
  }
  EXPORT_SYMBOL(path_get);
  
  /**
   * path_put - put a reference to a path
   * @path: path to put the reference to
   *
   * Given a path decrement the reference count to the dentry and the vfsmount.
   */
  void path_put(const struct path *path)
  {
  	dput(path->dentry);
  	mntput(path->mnt);
  }
  EXPORT_SYMBOL(path_put);
  
  #define EMBEDDED_LEVELS 2
  struct nameidata {
  	struct path	path;
  	struct qstr	last;
  	struct path	root;
  	struct inode	*inode; /* path.dentry.d_inode */
  	unsigned int	flags;
  	unsigned	seq, m_seq;
  	int		last_type;
  	unsigned	depth;
  	int		total_link_count;
  	struct saved {
  		struct path link;
  		void *cookie;
  		const char *name;
  		struct inode *inode;
  		unsigned seq;
  	} *stack, internal[EMBEDDED_LEVELS];
  	struct filename	*name;
  	struct nameidata *saved;
  	unsigned	root_seq;
  	int		dfd;
  };
  
  static void set_nameidata(struct nameidata *p, int dfd, struct filename *name)
  {
  	struct nameidata *old = current->nameidata;
  	p->stack = p->internal;
  	p->dfd = dfd;
  	p->name = name;
  	p->total_link_count = old ? old->total_link_count : 0;
  	p->saved = old;
  	current->nameidata = p;
  }
  
  static void restore_nameidata(void)
  {
  	struct nameidata *now = current->nameidata, *old = now->saved;
  
  	current->nameidata = old;
  	if (old)
  		old->total_link_count = now->total_link_count;
  	if (now->stack != now->internal) {
  		kfree(now->stack);
  		now->stack = now->internal;
  	}
  }
  
  static int __nd_alloc_stack(struct nameidata *nd)
  {
  	struct saved *p;
  
  	if (nd->flags & LOOKUP_RCU) {
  		p= kmalloc(MAXSYMLINKS * sizeof(struct saved),
  				  GFP_ATOMIC);
  		if (unlikely(!p))
  			return -ECHILD;
  	} else {
  		p= kmalloc(MAXSYMLINKS * sizeof(struct saved),
  				  GFP_KERNEL);
  		if (unlikely(!p))
  			return -ENOMEM;
  	}
  	memcpy(p, nd->internal, sizeof(nd->internal));
  	nd->stack = p;
  	return 0;
  }
  
  /**
   * path_connected - Verify that a path->dentry is below path->mnt.mnt_root
   * @path: nameidate to verify
   *
   * Rename can sometimes move a file or directory outside of a bind
   * mount, path_connected allows those cases to be detected.
   */
  static bool path_connected(const struct path *path)
  {
  	struct vfsmount *mnt = path->mnt;
  
  	/* Only bind mounts can have disconnected paths */
  	if (mnt->mnt_root == mnt->mnt_sb->s_root)
  		return true;
  
  	return is_subdir(path->dentry, mnt->mnt_root);
  }
  
  static inline int nd_alloc_stack(struct nameidata *nd)
  {
  	if (likely(nd->depth != EMBEDDED_LEVELS))
  		return 0;
  	if (likely(nd->stack != nd->internal))
  		return 0;
  	return __nd_alloc_stack(nd);
  }
  
  static void drop_links(struct nameidata *nd)
  {
  	int i = nd->depth;
  	while (i--) {
  		struct saved *last = nd->stack + i;
  		struct inode *inode = last->inode;
  		if (last->cookie && inode->i_op->put_link) {
  			inode->i_op->put_link(inode, last->cookie);
  			last->cookie = NULL;
  		}
  	}
  }
  
  static void terminate_walk(struct nameidata *nd)
  {
  	drop_links(nd);
  	if (!(nd->flags & LOOKUP_RCU)) {
  		int i;
  		path_put(&nd->path);
  		for (i = 0; i < nd->depth; i++)
  			path_put(&nd->stack[i].link);
  		if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
  			path_put(&nd->root);
  			nd->root.mnt = NULL;
  		}
  	} else {
  		nd->flags &= ~LOOKUP_RCU;
  		if (!(nd->flags & LOOKUP_ROOT))
  			nd->root.mnt = NULL;
  		rcu_read_unlock();
  	}
  	nd->depth = 0;
  }
  
  /* path_put is needed afterwards regardless of success or failure */
  static bool legitimize_path(struct nameidata *nd,
  			    struct path *path, unsigned seq)
  {
  	int res = __legitimize_mnt(path->mnt, nd->m_seq);
  	if (unlikely(res)) {
  		if (res > 0)
  			path->mnt = NULL;
  		path->dentry = NULL;
  		return false;
  	}
  	if (unlikely(!lockref_get_not_dead(&path->dentry->d_lockref))) {
  		path->dentry = NULL;
  		return false;
  	}
  	return !read_seqcount_retry(&path->dentry->d_seq, seq);
  }
  
  static bool legitimize_links(struct nameidata *nd)
  {
  	int i;
  	for (i = 0; i < nd->depth; i++) {
  		struct saved *last = nd->stack + i;
  		if (unlikely(!legitimize_path(nd, &last->link, last->seq))) {
  			drop_links(nd);
  			nd->depth = i + 1;
  			return false;
  		}
  	}
  	return true;
  }
  
  /*
   * Path walking has 2 modes, rcu-walk and ref-walk (see
   * Documentation/filesystems/path-lookup.txt).  In situations when we can't
   * continue in RCU mode, we attempt to drop out of rcu-walk mode and grab
   * normal reference counts on dentries and vfsmounts to transition to rcu-walk
   * mode.  Refcounts are grabbed at the last known good point before rcu-walk
   * got stuck, so ref-walk may continue from there. If this is not successful
   * (eg. a seqcount has changed), then failure is returned and it's up to caller
   * to restart the path walk from the beginning in ref-walk mode.
   */
  
  /**
   * unlazy_walk - try to switch to ref-walk mode.
   * @nd: nameidata pathwalk data
   * @dentry: child of nd->path.dentry or NULL
   * @seq: seq number to check dentry against
   * Returns: 0 on success, -ECHILD on failure
   *
   * unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry
   * for ref-walk mode.  @dentry must be a path found by a do_lookup call on
   * @nd or NULL.  Must be called from rcu-walk context.
   * Nothing should touch nameidata between unlazy_walk() failure and
   * terminate_walk().
   */
  static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq)
  {
  	struct dentry *parent = nd->path.dentry;
  
  	BUG_ON(!(nd->flags & LOOKUP_RCU));
  
  	nd->flags &= ~LOOKUP_RCU;
  	if (unlikely(!legitimize_links(nd)))
  		goto out2;
  	if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq)))
  		goto out2;
  	if (unlikely(!lockref_get_not_dead(&parent->d_lockref)))
  		goto out1;
  
  	/*
  	 * For a negative lookup, the lookup sequence point is the parents
  	 * sequence point, and it only needs to revalidate the parent dentry.
  	 *
  	 * For a positive lookup, we need to move both the parent and the
  	 * dentry from the RCU domain to be properly refcounted. And the
  	 * sequence number in the dentry validates *both* dentry counters,
  	 * since we checked the sequence number of the parent after we got
  	 * the child sequence number. So we know the parent must still
  	 * be valid if the child sequence number is still valid.
  	 */
  	if (!dentry) {
  		if (read_seqcount_retry(&parent->d_seq, nd->seq))
  			goto out;
  		BUG_ON(nd->inode != parent->d_inode);
  	} else {
  		if (!lockref_get_not_dead(&dentry->d_lockref))
  			goto out;
  		if (read_seqcount_retry(&dentry->d_seq, seq))
  			goto drop_dentry;
  	}
  
  	/*
  	 * Sequence counts matched. Now make sure that the root is
  	 * still valid and get it if required.
  	 */
  	if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
  		if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq))) {
  			rcu_read_unlock();
  			dput(dentry);
  			return -ECHILD;
  		}
  	}
  
  	rcu_read_unlock();
  	return 0;
  
  drop_dentry:
  	rcu_read_unlock();
  	dput(dentry);
  	goto drop_root_mnt;
  out2:
  	nd->path.mnt = NULL;
  out1:
  	nd->path.dentry = NULL;
  out:
  	rcu_read_unlock();
  drop_root_mnt:
  	if (!(nd->flags & LOOKUP_ROOT))
  		nd->root.mnt = NULL;
  	return -ECHILD;
  }
  
  static int unlazy_link(struct nameidata *nd, struct path *link, unsigned seq)
  {
  	if (unlikely(!legitimize_path(nd, link, seq))) {
  		drop_links(nd);
  		nd->depth = 0;
  		nd->flags &= ~LOOKUP_RCU;
  		nd->path.mnt = NULL;
  		nd->path.dentry = NULL;
  		if (!(nd->flags & LOOKUP_ROOT))
  			nd->root.mnt = NULL;
  		rcu_read_unlock();
  	} else if (likely(unlazy_walk(nd, NULL, 0)) == 0) {
  		return 0;
  	}
  	path_put(link);
  	return -ECHILD;
  }
  
  static inline int d_revalidate(struct dentry *dentry, unsigned int flags)
  {
  	return dentry->d_op->d_revalidate(dentry, flags);
  }
  
  /**
   * complete_walk - successful completion of path walk
   * @nd:  pointer nameidata
   *
   * If we had been in RCU mode, drop out of it and legitimize nd->path.
   * Revalidate the final result, unless we'd already done that during
   * the path walk or the filesystem doesn't ask for it.  Return 0 on
   * success, -error on failure.  In case of failure caller does not
   * need to drop nd->path.
   */
  static int complete_walk(struct nameidata *nd)
  {
  	struct dentry *dentry = nd->path.dentry;
  	int status;
  
  	if (nd->flags & LOOKUP_RCU) {
  		if (!(nd->flags & LOOKUP_ROOT))
  			nd->root.mnt = NULL;
  		if (unlikely(unlazy_walk(nd, NULL, 0)))
  			return -ECHILD;
  	}
  
  	if (likely(!(nd->flags & LOOKUP_JUMPED)))
  		return 0;
  
  	if (likely(!(dentry->d_flags & DCACHE_OP_WEAK_REVALIDATE)))
  		return 0;
  
  	status = dentry->d_op->d_weak_revalidate(dentry, nd->flags);
  	if (status > 0)
  		return 0;
  
  	if (!status)
  		status = -ESTALE;
  
  	return status;
  }
  
  static void set_root(struct nameidata *nd)
  {
  	get_fs_root(current->fs, &nd->root);
  }
  
  static void set_root_rcu(struct nameidata *nd)
  {
  	struct fs_struct *fs = current->fs;
  	unsigned seq;
  
  	do {
  		seq = read_seqcount_begin(&fs->seq);
  		nd->root = fs->root;
  		nd->root_seq = __read_seqcount_begin(&nd->root.dentry->d_seq);
  	} while (read_seqcount_retry(&fs->seq, seq));
  }
  
  static void path_put_conditional(struct path *path, struct nameidata *nd)
  {
  	dput(path->dentry);
  	if (path->mnt != nd->path.mnt)
  		mntput(path->mnt);
  }
  
  static inline void path_to_nameidata(const struct path *path,
  					struct nameidata *nd)
  {
  	if (!(nd->flags & LOOKUP_RCU)) {
  		dput(nd->path.dentry);
  		if (nd->path.mnt != path->mnt)
  			mntput(nd->path.mnt);
  	}
  	nd->path.mnt = path->mnt;
  	nd->path.dentry = path->dentry;
  }
  
  /*
   * Helper to directly jump to a known parsed path from ->follow_link,
   * caller must have taken a reference to path beforehand.
   */
  void nd_jump_link(struct path *path)
  {
  	struct nameidata *nd = current->nameidata;
  	path_put(&nd->path);
  
  	nd->path = *path;
  	nd->inode = nd->path.dentry->d_inode;
  	nd->flags |= LOOKUP_JUMPED;
  }
  
  static inline void put_link(struct nameidata *nd)
  {
  	struct saved *last = nd->stack + --nd->depth;
  	struct inode *inode = last->inode;
  	if (last->cookie && inode->i_op->put_link)
  		inode->i_op->put_link(inode, last->cookie);
  	if (!(nd->flags & LOOKUP_RCU))
  		path_put(&last->link);
  }
  
  int sysctl_protected_symlinks __read_mostly = 1;
  int sysctl_protected_hardlinks __read_mostly = 1;
  
  /**
   * may_follow_link - Check symlink following for unsafe situations
   * @nd: nameidata pathwalk data
   *
   * In the case of the sysctl_protected_symlinks sysctl being enabled,
   * CAP_DAC_OVERRIDE needs to be specifically ignored if the symlink is
   * in a sticky world-writable directory. This is to protect privileged
   * processes from failing races against path names that may change out
   * from under them by way of other users creating malicious symlinks.
   * It will permit symlinks to be followed only when outside a sticky
   * world-writable directory, or when the uid of the symlink and follower
   * match, or when the directory owner matches the symlink's owner.
   *
   * Returns 0 if following the symlink is allowed, -ve on error.
   */
  static inline int may_follow_link(struct nameidata *nd)
  {
  	const struct inode *inode;
  	const struct inode *parent;
  
  	if (!sysctl_protected_symlinks)
  		return 0;
  
  	/* Allowed if owner and follower match. */
  	inode = nd->stack[0].inode;
  	if (uid_eq(current_cred()->fsuid, inode->i_uid))
  		return 0;
  
  	/* Allowed if parent directory not sticky and world-writable. */
  	parent = nd->inode;
  	if ((parent->i_mode & (S_ISVTX|S_IWOTH)) != (S_ISVTX|S_IWOTH))
  		return 0;
  
  	/* Allowed if parent directory and link owner match. */
  	if (uid_eq(parent->i_uid, inode->i_uid))
  		return 0;
  
  	if (nd->flags & LOOKUP_RCU)
  		return -ECHILD;
  
  	audit_log_link_denied("follow_link", &nd->stack[0].link);
  	return -EACCES;
  }
  
  /**
   * safe_hardlink_source - Check for safe hardlink conditions
   * @inode: the source inode to hardlink from
   *
   * Return false if at least one of the following conditions:
   *    - inode is not a regular file
   *    - inode is setuid
   *    - inode is setgid and group-exec
   *    - access failure for read and write
   *
   * Otherwise returns true.
   */
  static bool safe_hardlink_source(struct inode *inode)
  {
  	umode_t mode = inode->i_mode;
  
  	/* Special files should not get pinned to the filesystem. */
  	if (!S_ISREG(mode))
  		return false;
  
  	/* Setuid files should not get pinned to the filesystem. */
  	if (mode & S_ISUID)
  		return false;
  
  	/* Executable setgid files should not get pinned to the filesystem. */
  	if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP))
  		return false;
  
  	/* Hardlinking to unreadable or unwritable sources is dangerous. */
  	if (inode_permission(inode, MAY_READ | MAY_WRITE))
  		return false;
  
  	return true;
  }
  
  /**
   * may_linkat - Check permissions for creating a hardlink
   * @link: the source to hardlink from
   *
   * Block hardlink when all of:
   *  - sysctl_protected_hardlinks enabled
   *  - fsuid does not match inode
   *  - hardlink source is unsafe (see safe_hardlink_source() above)
   *  - not CAP_FOWNER in a namespace with the inode owner uid mapped
   *
   * Returns 0 if successful, -ve on error.
   */
  static int may_linkat(struct path *link)
  {
  	struct inode *inode;
  
  	if (!sysctl_protected_hardlinks)
  		return 0;
  
  	inode = link->dentry->d_inode;
  
  	/* Source inode owner (or CAP_FOWNER) can hardlink all they like,
  	 * otherwise, it must be a safe source.
  	 */
  	if (inode_owner_or_capable(inode) || safe_hardlink_source(inode))
  		return 0;
  
  	audit_log_link_denied("linkat", link);
  	return -EPERM;
  }
  
  static __always_inline
  const char *get_link(struct nameidata *nd)
  {
  	struct saved *last = nd->stack + nd->depth - 1;
  	struct dentry *dentry = last->link.dentry;
  	struct inode *inode = last->inode;
  	int error;
  	const char *res;
  
  	if (!(nd->flags & LOOKUP_RCU)) {
  		touch_atime(&last->link);
  		cond_resched();
  	} else if (atime_needs_update(&last->link, inode)) {
  		if (unlikely(unlazy_walk(nd, NULL, 0)))
  			return ERR_PTR(-ECHILD);
  		touch_atime(&last->link);
  	}
  
  	error = security_inode_follow_link(dentry, inode,
  					   nd->flags & LOOKUP_RCU);
  	if (unlikely(error))
  		return ERR_PTR(error);
  
  	nd->last_type = LAST_BIND;
  	res = inode->i_link;
  	if (!res) {
  		if (nd->flags & LOOKUP_RCU) {
  			if (unlikely(unlazy_walk(nd, NULL, 0)))
  				return ERR_PTR(-ECHILD);
  		}
  		res = inode->i_op->follow_link(dentry, &last->cookie);
  		if (IS_ERR_OR_NULL(res)) {
  			last->cookie = NULL;
  			return res;
  		}
  	}
  	if (*res == '/') {
  		if (nd->flags & LOOKUP_RCU) {
  			struct dentry *d;
  			if (!nd->root.mnt)
  				set_root_rcu(nd);
  			nd->path = nd->root;
  			d = nd->path.dentry;
  			nd->inode = d->d_inode;
  			nd->seq = nd->root_seq;
  			if (unlikely(read_seqcount_retry(&d->d_seq, nd->seq)))
  				return ERR_PTR(-ECHILD);
  		} else {
  			if (!nd->root.mnt)
  				set_root(nd);
  			path_put(&nd->path);
  			nd->path = nd->root;
  			path_get(&nd->root);
  			nd->inode = nd->path.dentry->d_inode;
  		}
  		nd->flags |= LOOKUP_JUMPED;
  		while (unlikely(*++res == '/'))
  			;
  	}
  	if (!*res)
  		res = NULL;
  	return res;
  }
  
  /*
   * follow_up - Find the mountpoint of path's vfsmount
   *
   * Given a path, find the mountpoint of its source file system.
   * Replace @path with the path of the mountpoint in the parent mount.
   * Up is towards /.
   *
   * Return 1 if we went up a level and 0 if we were already at the
   * root.
   */
  int follow_up(struct path *path)
  {
  	struct mount *mnt = real_mount(path->mnt);
  	struct mount *parent;
  	struct dentry *mountpoint;
  
  	read_seqlock_excl(&mount_lock);
  	parent = mnt->mnt_parent;
  	if (parent == mnt) {
  		read_sequnlock_excl(&mount_lock);
  		return 0;
  	}
  	mntget(&parent->mnt);
  	mountpoint = dget(mnt->mnt_mountpoint);
  	read_sequnlock_excl(&mount_lock);
  	dput(path->dentry);
  	path->dentry = mountpoint;
  	mntput(path->mnt);
  	path->mnt = &parent->mnt;
  	return 1;
  }
  EXPORT_SYMBOL(follow_up);
  
  /*
   * Perform an automount
   * - return -EISDIR to tell follow_managed() to stop and return the path we
   *   were called with.
   */
  static int follow_automount(struct path *path, struct nameidata *nd,
  			    bool *need_mntput)
  {
  	struct vfsmount *mnt;
  	int err;
  
  	if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
  		return -EREMOTE;
  
  	/* We don't want to mount if someone's just doing a stat -
  	 * unless they're stat'ing a directory and appended a '/' to
  	 * the name.
  	 *
  	 * We do, however, want to mount if someone wants to open or
  	 * create a file of any type under the mountpoint, wants to
  	 * traverse through the mountpoint or wants to open the
  	 * mounted directory.  Also, autofs may mark negative dentries
  	 * as being automount points.  These will need the attentions
  	 * of the daemon to instantiate them before they can be used.
  	 */
  	if (!(nd->flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
  			   LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
  	    path->dentry->d_inode)
  		return -EISDIR;
  
  	nd->total_link_count++;
  	if (nd->total_link_count >= 40)
  		return -ELOOP;
  
  	mnt = path->dentry->d_op->d_automount(path);
  	if (IS_ERR(mnt)) {
  		/*
  		 * The filesystem is allowed to return -EISDIR here to indicate
  		 * it doesn't want to automount.  For instance, autofs would do
  		 * this so that its userspace daemon can mount on this dentry.
  		 *
  		 * However, we can only permit this if it's a terminal point in
  		 * the path being looked up; if it wasn't then the remainder of
  		 * the path is inaccessible and we should say so.
  		 */
  		if (PTR_ERR(mnt) == -EISDIR && (nd->flags & LOOKUP_PARENT))
  			return -EREMOTE;
  		return PTR_ERR(mnt);
  	}
  
  	if (!mnt) /* mount collision */
  		return 0;
  
  	if (!*need_mntput) {
  		/* lock_mount() may release path->mnt on error */
  		mntget(path->mnt);
  		*need_mntput = true;
  	}
  	err = finish_automount(mnt, path);
  
  	switch (err) {
  	case -EBUSY:
  		/* Someone else made a mount here whilst we were busy */
  		return 0;
  	case 0:
  		path_put(path);
  		path->mnt = mnt;
  		path->dentry = dget(mnt->mnt_root);
  		return 0;
  	default:
  		return err;
  	}
  
  }
  
  /*
   * Handle a dentry that is managed in some way.
   * - Flagged for transit management (autofs)
   * - Flagged as mountpoint
   * - Flagged as automount point
   *
   * This may only be called in refwalk mode.
   *
   * Serialization is taken care of in namespace.c
   */
  static int follow_managed(struct path *path, struct nameidata *nd)
  {
  	struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */
  	unsigned managed;
  	bool need_mntput = false;
  	int ret = 0;
  
  	/* Given that we're not holding a lock here, we retain the value in a
  	 * local variable for each dentry as we look at it so that we don't see
  	 * the components of that value change under us */
  	while (managed = ACCESS_ONCE(path->dentry->d_flags),
  	       managed &= DCACHE_MANAGED_DENTRY,
  	       unlikely(managed != 0)) {
  		/* Allow the filesystem to manage the transit without i_mutex
  		 * being held. */
  		if (managed & DCACHE_MANAGE_TRANSIT) {
  			BUG_ON(!path->dentry->d_op);
  			BUG_ON(!path->dentry->d_op->d_manage);
  			ret = path->dentry->d_op->d_manage(path->dentry, false);
  			if (ret < 0)
  				break;
  		}
  
  		/* Transit to a mounted filesystem. */
  		if (managed & DCACHE_MOUNTED) {
  			struct vfsmount *mounted = lookup_mnt(path);
  			if (mounted) {
  				dput(path->dentry);
  				if (need_mntput)
  					mntput(path->mnt);
  				path->mnt = mounted;
  				path->dentry = dget(mounted->mnt_root);
  				need_mntput = true;
  				continue;
  			}
  
  			/* Something is mounted on this dentry in another
  			 * namespace and/or whatever was mounted there in this
  			 * namespace got unmounted before lookup_mnt() could
  			 * get it */
  		}
  
  		/* Handle an automount point */
  		if (managed & DCACHE_NEED_AUTOMOUNT) {
  			ret = follow_automount(path, nd, &need_mntput);
  			if (ret < 0)
  				break;
  			continue;
  		}
  
  		/* We didn't change the current path point */
  		break;
  	}
  
  	if (need_mntput && path->mnt == mnt)
  		mntput(path->mnt);
  	if (ret == -EISDIR)
  		ret = 0;
  	if (need_mntput)
  		nd->flags |= LOOKUP_JUMPED;
  	if (unlikely(ret < 0))
  		path_put_conditional(path, nd);
  	return ret;
  }
  
  int follow_down_one(struct path *path)
  {
  	struct vfsmount *mounted;
  
  	mounted = lookup_mnt(path);
  	if (mounted) {
  		dput(path->dentry);
  		mntput(path->mnt);
  		path->mnt = mounted;
  		path->dentry = dget(mounted->mnt_root);
  		return 1;
  	}
  	return 0;
  }
  EXPORT_SYMBOL(follow_down_one);
  
  static inline int managed_dentry_rcu(struct dentry *dentry)
  {
  	return (dentry->d_flags & DCACHE_MANAGE_TRANSIT) ?
  		dentry->d_op->d_manage(dentry, true) : 0;
  }
  
  /*
   * Try to skip to top of mountpoint pile in rcuwalk mode.  Fail if
   * we meet a managed dentry that would need blocking.
   */
  static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
  			       struct inode **inode, unsigned *seqp)
  {
  	for (;;) {
  		struct mount *mounted;
  		/*
  		 * Don't forget we might have a non-mountpoint managed dentry
  		 * that wants to block transit.
  		 */
  		switch (managed_dentry_rcu(path->dentry)) {
  		case -ECHILD:
  		default:
  			return false;
  		case -EISDIR:
  			return true;
  		case 0:
  			break;
  		}
  
  		if (!d_mountpoint(path->dentry))
  			return !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
  
  		mounted = __lookup_mnt(path->mnt, path->dentry);
  		if (!mounted)
  			break;
  		path->mnt = &mounted->mnt;
  		path->dentry = mounted->mnt.mnt_root;
  		nd->flags |= LOOKUP_JUMPED;
  		*seqp = read_seqcount_begin(&path->dentry->d_seq);
  		/*
  		 * Update the inode too. We don't need to re-check the
  		 * dentry sequence number here after this d_inode read,
  		 * because a mount-point is always pinned.
  		 */
  		*inode = path->dentry->d_inode;
  	}
  	return !read_seqretry(&mount_lock, nd->m_seq) &&
  		!(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
  }
  
  static int follow_dotdot_rcu(struct nameidata *nd)
  {
  	struct inode *inode = nd->inode;
  	if (!nd->root.mnt)
  		set_root_rcu(nd);
  
  	while (1) {
  		if (path_equal(&nd->path, &nd->root))
  			break;
  		if (nd->path.dentry != nd->path.mnt->mnt_root) {
  			struct dentry *old = nd->path.dentry;
  			struct dentry *parent = old->d_parent;
  			unsigned seq;
  
  			inode = parent->d_inode;
  			seq = read_seqcount_begin(&parent->d_seq);
  			if (unlikely(read_seqcount_retry(&old->d_seq, nd->seq)))
  				return -ECHILD;
  			nd->path.dentry = parent;
  			nd->seq = seq;
  			if (unlikely(!path_connected(&nd->path)))
  				return -ENOENT;
  			break;
  		} else {
  			struct mount *mnt = real_mount(nd->path.mnt);
  			struct mount *mparent = mnt->mnt_parent;
  			struct dentry *mountpoint = mnt->mnt_mountpoint;
  			struct inode *inode2 = mountpoint->d_inode;
  			unsigned seq = read_seqcount_begin(&mountpoint->d_seq);
  			if (unlikely(read_seqretry(&mount_lock, nd->m_seq)))
  				return -ECHILD;
  			if (&mparent->mnt == nd->path.mnt)
  				break;
  			/* we know that mountpoint was pinned */
  			nd->path.dentry = mountpoint;
  			nd->path.mnt = &mparent->mnt;
  			inode = inode2;
  			nd->seq = seq;
  		}
  	}
  	while (unlikely(d_mountpoint(nd->path.dentry))) {
  		struct mount *mounted;
  		mounted = __lookup_mnt(nd->path.mnt, nd->path.dentry);
  		if (unlikely(read_seqretry(&mount_lock, nd->m_seq)))
  			return -ECHILD;
  		if (!mounted)
  			break;
  		nd->path.mnt = &mounted->mnt;
  		nd->path.dentry = mounted->mnt.mnt_root;
  		inode = nd->path.dentry->d_inode;
  		nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
  	}
  	nd->inode = inode;
  	return 0;
  }
  
  /*
   * Follow down to the covering mount currently visible to userspace.  At each
   * point, the filesystem owning that dentry may be queried as to whether the
   * caller is permitted to proceed or not.
   */
  int follow_down(struct path *path)
  {
  	unsigned managed;
  	int ret;
  
  	while (managed = ACCESS_ONCE(path->dentry->d_flags),
  	       unlikely(managed & DCACHE_MANAGED_DENTRY)) {
  		/* Allow the filesystem to manage the transit without i_mutex
  		 * being held.
  		 *
  		 * We indicate to the filesystem if someone is trying to mount
  		 * something here.  This gives autofs the chance to deny anyone
  		 * other than its daemon the right to mount on its
  		 * superstructure.
  		 *
  		 * The filesystem may sleep at this point.
  		 */
  		if (managed & DCACHE_MANAGE_TRANSIT) {
  			BUG_ON(!path->dentry->d_op);
  			BUG_ON(!path->dentry->d_op->d_manage);
  			ret = path->dentry->d_op->d_manage(
  				path->dentry, false);
  			if (ret < 0)
  				return ret == -EISDIR ? 0 : ret;
  		}
  
  		/* Transit to a mounted filesystem. */
  		if (managed & DCACHE_MOUNTED) {
  			struct vfsmount *mounted = lookup_mnt(path);
  			if (!mounted)
  				break;
  			dput(path->dentry);
  			mntput(path->mnt);
  			path->mnt = mounted;
  			path->dentry = dget(mounted->mnt_root);
  			continue;
  		}
  
  		/* Don't handle automount points here */
  		break;
  	}
  	return 0;
  }
  EXPORT_SYMBOL(follow_down);
  
  /*
   * Skip to top of mountpoint pile in refwalk mode for follow_dotdot()
   */
  static void follow_mount(struct path *path)
  {
  	while (d_mountpoint(path->dentry)) {
  		struct vfsmount *mounted = lookup_mnt(path);
  		if (!mounted)
  			break;
  		dput(path->dentry);
  		mntput(path->mnt);
  		path->mnt = mounted;
  		path->dentry = dget(mounted->mnt_root);
  	}
  }
  
  static int follow_dotdot(struct nameidata *nd)
  {
  	if (!nd->root.mnt)
  		set_root(nd);
  
  	while(1) {
  		struct dentry *old = nd->path.dentry;
  
  		if (nd->path.dentry == nd->root.dentry &&
  		    nd->path.mnt == nd->root.mnt) {
  			break;
  		}
  		if (nd->path.dentry != nd->path.mnt->mnt_root) {
  			/* rare case of legitimate dget_parent()... */
  			nd->path.dentry = dget_parent(nd->path.dentry);
  			dput(old);
  			if (unlikely(!path_connected(&nd->path)))
  				return -ENOENT;
  			break;
  		}
  		if (!follow_up(&nd->path))
  			break;
  	}
  	follow_mount(&nd->path);
  	nd->inode = nd->path.dentry->d_inode;
  	return 0;
  }
  
  /*
   * This looks up the name in dcache, possibly revalidates the old dentry and
   * allocates a new one if not found or not valid.  In the need_lookup argument
   * returns whether i_op->lookup is necessary.
   *
   * dir->d_inode->i_mutex must be held
   */
  static struct dentry *lookup_dcache(struct qstr *name, struct dentry *dir,
  				    unsigned int flags, bool *need_lookup)
  {
  	struct dentry *dentry;
  	int error;
  
  	*need_lookup = false;
  	dentry = d_lookup(dir, name);
  	if (dentry) {
  		if (dentry->d_flags & DCACHE_OP_REVALIDATE) {
  			error = d_revalidate(dentry, flags);
  			if (unlikely(error <= 0)) {
  				if (error < 0) {
  					dput(dentry);
  					return ERR_PTR(error);
  				} else {
  					d_invalidate(dentry);
  					dput(dentry);
  					dentry = NULL;
  				}
  			}
  		}
  	}
  
  	if (!dentry) {
  		dentry = d_alloc(dir, name);
  		if (unlikely(!dentry))
  			return ERR_PTR(-ENOMEM);
  
  		*need_lookup = true;
  	}
  	return dentry;
  }
  
  /*
   * Call i_op->lookup on the dentry.  The dentry must be negative and
   * unhashed.
   *
   * dir->d_inode->i_mutex must be held
   */
  static struct dentry *lookup_real(struct inode *dir, struct dentry *dentry,
  				  unsigned int flags)
  {
  	struct dentry *old;
  
  	/* Don't create child dentry for a dead directory. */
  	if (unlikely(IS_DEADDIR(dir))) {
  		dput(dentry);
  		return ERR_PTR(-ENOENT);
  	}
  
  	old = dir->i_op->lookup(dir, dentry, flags);
  	if (unlikely(old)) {
  		dput(dentry);
  		dentry = old;
  	}
  	return dentry;
  }
  
  static struct dentry *__lookup_hash(struct qstr *name,
  		struct dentry *base, unsigned int flags)
  {
  	bool need_lookup;
  	struct dentry *dentry;
  
  	dentry = lookup_dcache(name, base, flags, &need_lookup);
  	if (!need_lookup)
  		return dentry;
  
  	return lookup_real(base->d_inode, dentry, flags);
  }
  
  /*
   *  It's more convoluted than I'd like it to be, but... it's still fairly
   *  small and for now I'd prefer to have fast path as straight as possible.
   *  It _is_ time-critical.
   */
  static int lookup_fast(struct nameidata *nd,
  		       struct path *path, struct inode **inode,
  		       unsigned *seqp)
  {
  	struct vfsmount *mnt = nd->path.mnt;
  	struct dentry *dentry, *parent = nd->path.dentry;
  	int need_reval = 1;
  	int status = 1;
  	int err;
  
  	/*
  	 * Rename seqlock is not required here because in the off chance
  	 * of a false negative due to a concurrent rename, we're going to
  	 * do the non-racy lookup, below.
  	 */
  	if (nd->flags & LOOKUP_RCU) {
  		unsigned seq;
  		bool negative;
  		dentry = __d_lookup_rcu(parent, &nd->last, &seq);
  		if (!dentry)
  			goto unlazy;
  
  		/*
  		 * This sequence count validates that the inode matches
  		 * the dentry name information from lookup.
  		 */
  		*inode = d_backing_inode(dentry);
  		negative = d_is_negative(dentry);
  		if (read_seqcount_retry(&dentry->d_seq, seq))
  			return -ECHILD;
  
  		/*
  		 * This sequence count validates that the parent had no
  		 * changes while we did the lookup of the dentry above.
  		 *
  		 * The memory barrier in read_seqcount_begin of child is
  		 *  enough, we can use __read_seqcount_retry here.
  		 */
  		if (__read_seqcount_retry(&parent->d_seq, nd->seq))
  			return -ECHILD;
  
  		*seqp = seq;
  		if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) {
  			status = d_revalidate(dentry, nd->flags);
  			if (unlikely(status <= 0)) {
  				if (status != -ECHILD)
  					need_reval = 0;
  				goto unlazy;
  			}
  		}
  		/*
  		 * Note: do negative dentry check after revalidation in
  		 * case that drops it.
  		 */
  		if (negative)
  			return -ENOENT;
  		path->mnt = mnt;
  		path->dentry = dentry;
  		if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
  			return 0;
  unlazy:
  		if (unlazy_walk(nd, dentry, seq))
  			return -ECHILD;
  	} else {
  		dentry = __d_lookup(parent, &nd->last);
  	}
  
  	if (unlikely(!dentry))
  		goto need_lookup;
  
  	if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE) && need_reval)
  		status = d_revalidate(dentry, nd->flags);
  	if (unlikely(status <= 0)) {
  		if (status < 0) {
  			dput(dentry);
  			return status;
  		}
  		d_invalidate(dentry);
  		dput(dentry);
  		goto need_lookup;
  	}
  
  	if (unlikely(d_is_negative(dentry))) {
  		dput(dentry);
  		return -ENOENT;
  	}
  	path->mnt = mnt;
  	path->dentry = dentry;
  	err = follow_managed(path, nd);
  	if (likely(!err))
  		*inode = d_backing_inode(path->dentry);
  	return err;
  
  need_lookup:
  	return 1;
  }
  
  /* Fast lookup failed, do it the slow way */
  static int lookup_slow(struct nameidata *nd, struct path *path)
  {
  	struct dentry *dentry, *parent;
  
  	parent = nd->path.dentry;
  	BUG_ON(nd->inode != parent->d_inode);
  
  	mutex_lock(&parent->d_inode->i_mutex);
  	dentry = __lookup_hash(&nd->last, parent, nd->flags);
  	mutex_unlock(&parent->d_inode->i_mutex);
  	if (IS_ERR(dentry))
  		return PTR_ERR(dentry);
  	path->mnt = nd->path.mnt;
  	path->dentry = dentry;
  	return follow_managed(path, nd);
  }
  
  static inline int may_lookup(struct nameidata *nd)
  {
  	if (nd->flags & LOOKUP_RCU) {
  		int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK);
  		if (err != -ECHILD)
  			return err;
  		if (unlazy_walk(nd, NULL, 0))
  			return -ECHILD;
  	}
  	return inode_permission(nd->inode, MAY_EXEC);
  }
  
  static inline int handle_dots(struct nameidata *nd, int type)
  {
  	if (type == LAST_DOTDOT) {
  		if (nd->flags & LOOKUP_RCU) {
  			return follow_dotdot_rcu(nd);
  		} else
  			return follow_dotdot(nd);
  	}
  	return 0;
  }
  
  static int pick_link(struct nameidata *nd, struct path *link,
  		     struct inode *inode, unsigned seq)
  {
  	int error;
  	struct saved *last;
  	if (unlikely(nd->total_link_count++ >= MAXSYMLINKS)) {
  		path_to_nameidata(link, nd);
  		return -ELOOP;
  	}
  	if (!(nd->flags & LOOKUP_RCU)) {
  		if (link->mnt == nd->path.mnt)
  			mntget(link->mnt);
  	}
  	error = nd_alloc_stack(nd);
  	if (unlikely(error)) {
  		if (error == -ECHILD) {
  			if (unlikely(unlazy_link(nd, link, seq)))
  				return -ECHILD;
  			error = nd_alloc_stack(nd);
  		}
  		if (error) {
  			path_put(link);
  			return error;
  		}
  	}
  
  	last = nd->stack + nd->depth++;
  	last->link = *link;
  	last->cookie = NULL;
  	last->inode = inode;
  	last->seq = seq;
  	return 1;
  }
  
  /*
   * Do we need to follow links? We _really_ want to be able
   * to do this check without having to look at inode->i_op,
   * so we keep a cache of "no, this doesn't need follow_link"
   * for the common case.
   */
  static inline int should_follow_link(struct nameidata *nd, struct path *link,
  				     int follow,
  				     struct inode *inode, unsigned seq)
  {
  	if (likely(!d_is_symlink(link->dentry)))
  		return 0;
  	if (!follow)
  		return 0;
  	return pick_link(nd, link, inode, seq);
  }
  
  enum {WALK_GET = 1, WALK_PUT = 2};
  
  static int walk_component(struct nameidata *nd, int flags)
  {
  	struct path path;
  	struct inode *inode;
  	unsigned seq;
  	int err;
  	/*
  	 * "." and ".." are special - ".." especially so because it has
  	 * to be able to know about the current root directory and
  	 * parent relationships.
  	 */
  	if (unlikely(nd->last_type != LAST_NORM)) {
  		err = handle_dots(nd, nd->last_type);
  		if (flags & WALK_PUT)
  			put_link(nd);
  		return err;
  	}
  	err = lookup_fast(nd, &path, &inode, &seq);
  	if (unlikely(err)) {
  		if (err < 0)
  			return err;
  
  		err = lookup_slow(nd, &path);
  		if (err < 0)
  			return err;
  
  		inode = d_backing_inode(path.dentry);
  		seq = 0;	/* we are already out of RCU mode */
  		err = -ENOENT;
  		if (d_is_negative(path.dentry))
  			goto out_path_put;
  	}
  
  	if (flags & WALK_PUT)
  		put_link(nd);
  	err = should_follow_link(nd, &path, flags & WALK_GET, inode, seq);
  	if (unlikely(err))
  		return err;
  	path_to_nameidata(&path, nd);
  	nd->inode = inode;
  	nd->seq = seq;
  	return 0;
  
  out_path_put:
  	path_to_nameidata(&path, nd);
  	return err;
  }
  
  /*
   * We can do the critical dentry name comparison and hashing
   * operations one word at a time, but we are limited to:
   *
   * - Architectures with fast unaligned word accesses. We could
   *   do a "get_unaligned()" if this helps and is sufficiently
   *   fast.
   *
   * - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we
   *   do not trap on the (extremely unlikely) case of a page
   *   crossing operation.
   *
   * - Furthermore, we need an efficient 64-bit compile for the
   *   64-bit case in order to generate the "number of bytes in
   *   the final mask". Again, that could be replaced with a
   *   efficient population count instruction or similar.
   */
  #ifdef CONFIG_DCACHE_WORD_ACCESS
  
  #include <asm/word-at-a-time.h>
  
  #ifdef CONFIG_64BIT
  
  static inline unsigned int fold_hash(unsigned long hash)
  {
  	return hash_64(hash, 32);
  }
  
  #else	/* 32-bit case */
  
  #define fold_hash(x) (x)
  
  #endif
  
  unsigned int full_name_hash(const unsigned char *name, unsigned int len)
  {
  	unsigned long a, mask;
  	unsigned long hash = 0;
  
  	for (;;) {
  		a = load_unaligned_zeropad(name);
  		if (len < sizeof(unsigned long))
  			break;
  		hash += a;
  		hash *= 9;
  		name += sizeof(unsigned long);
  		len -= sizeof(unsigned long);
  		if (!len)
  			goto done;
  	}
  	mask = bytemask_from_count(len);
  	hash += mask & a;
  done:
  	return fold_hash(hash);
  }
  EXPORT_SYMBOL(full_name_hash);
  
  /*
   * Calculate the length and hash of the path component, and
   * return the "hash_len" as the result.
   */
  static inline u64 hash_name(const char *name)
  {
  	unsigned long a, b, adata, bdata, mask, hash, len;
  	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
  
  	hash = a = 0;
  	len = -sizeof(unsigned long);
  	do {
  		hash = (hash + a) * 9;
  		len += sizeof(unsigned long);
  		a = load_unaligned_zeropad(name+len);
  		b = a ^ REPEAT_BYTE('/');
  	} while (!(has_zero(a, &adata, &constants) | has_zero(b, &bdata, &constants)));
  
  	adata = prep_zero_mask(a, adata, &constants);
  	bdata = prep_zero_mask(b, bdata, &constants);
  
  	mask = create_zero_mask(adata | bdata);
  
  	hash += a & zero_bytemask(mask);
  	len += find_zero(mask);
  	return hashlen_create(fold_hash(hash), len);
  }
  
  #else
  
  unsigned int full_name_hash(const unsigned char *name, unsigned int len)
  {
  	unsigned long hash = init_name_hash();
  	while (len--)
  		hash = partial_name_hash(*name++, hash);
  	return end_name_hash(hash);
  }
  EXPORT_SYMBOL(full_name_hash);
  
  /*
   * We know there's a real path component here of at least
   * one character.
   */
  static inline u64 hash_name(const char *name)
  {
  	unsigned long hash = init_name_hash();
  	unsigned long len = 0, c;
  
  	c = (unsigned char)*name;
  	do {
  		len++;
  		hash = partial_name_hash(c, hash);
  		c = (unsigned char)name[len];
  	} while (c && c != '/');
  	return hashlen_create(end_name_hash(hash), len);
  }
  
  #endif
  
  /*
   * Name resolution.
   * This is the basic name resolution function, turning a pathname into
   * the final dentry. We expect 'base' to be positive and a directory.
   *
   * Returns 0 and nd will have valid dentry and mnt on success.
   * Returns error and drops reference to input namei data on failure.
   */
  static int link_path_walk(const char *name, struct nameidata *nd)
  {
  	int err;
  
  	while (*name=='/')
  		name++;
  	if (!*name)
  		return 0;
  
  	/* At this point we know we have a real path component. */
  	for(;;) {
  		u64 hash_len;
  		int type;
  
  		err = may_lookup(nd);
   		if (err)
  			return err;
  
  		hash_len = hash_name(name);
  
  		type = LAST_NORM;
  		if (name[0] == '.') switch (hashlen_len(hash_len)) {
  			case 2:
  				if (name[1] == '.') {
  					type = LAST_DOTDOT;
  					nd->flags |= LOOKUP_JUMPED;
  				}
  				break;
  			case 1:
  				type = LAST_DOT;
  		}
  		if (likely(type == LAST_NORM)) {
  			struct dentry *parent = nd->path.dentry;
  			nd->flags &= ~LOOKUP_JUMPED;
  			if (unlikely(parent->d_flags & DCACHE_OP_HASH)) {
  				struct qstr this = { { .hash_len = hash_len }, .name = name };
  				err = parent->d_op->d_hash(parent, &this);
  				if (err < 0)
  					return err;
  				hash_len = this.hash_len;
  				name = this.name;
  			}
  		}
  
  		nd->last.hash_len = hash_len;
  		nd->last.name = name;
  		nd->last_type = type;
  
  		name += hashlen_len(hash_len);
  		if (!*name)
  			goto OK;
  		/*
  		 * If it wasn't NUL, we know it was '/'. Skip that
  		 * slash, and continue until no more slashes.
  		 */
  		do {
  			name++;
  		} while (unlikely(*name == '/'));
  		if (unlikely(!*name)) {
  OK:
  			/* pathname body, done */
  			if (!nd->depth)
  				return 0;
  			name = nd->stack[nd->depth - 1].name;
  			/* trailing symlink, done */
  			if (!name)
  				return 0;
  			/* last component of nested symlink */
  			err = walk_component(nd, WALK_GET | WALK_PUT);
  		} else {
  			err = walk_component(nd, WALK_GET);
  		}
  		if (err < 0)
  			return err;
  
  		if (err) {
  			const char *s = get_link(nd);
  
  			if (unlikely(IS_ERR(s)))
  				return PTR_ERR(s);
  			err = 0;
  			if (unlikely(!s)) {
  				/* jumped */
  				put_link(nd);
  			} else {
  				nd->stack[nd->depth - 1].name = name;
  				name = s;
  				continue;
  			}
  		}
  		if (unlikely(!d_can_lookup(nd->path.dentry))) {
  			if (nd->flags & LOOKUP_RCU) {
  				if (unlazy_walk(nd, NULL, 0))
  					return -ECHILD;
  			}
  			return -ENOTDIR;
  		}
  	}
  }
  
  static const char *path_init(struct nameidata *nd, unsigned flags)
  {
  	int retval = 0;
  	const char *s = nd->name->name;
  
  	nd->last_type = LAST_ROOT; /* if there are only slashes... */
  	nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT;
  	nd->depth = 0;
  	nd->total_link_count = 0;
  	if (flags & LOOKUP_ROOT) {
  		struct dentry *root = nd->root.dentry;
  		struct inode *inode = root->d_inode;
  		if (*s) {
  			if (!d_can_lookup(root))
  				return ERR_PTR(-ENOTDIR);
  			retval = inode_permission(inode, MAY_EXEC);
  			if (retval)
  				return ERR_PTR(retval);
  		}
  		nd->path = nd->root;
  		nd->inode = inode;
  		if (flags & LOOKUP_RCU) {
  			rcu_read_lock();
  			nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
  			nd->root_seq = nd->seq;
  			nd->m_seq = read_seqbegin(&mount_lock);
  		} else {
  			path_get(&nd->path);
  		}
  		return s;
  	}
  
  	nd->root.mnt = NULL;
  
  	nd->m_seq = read_seqbegin(&mount_lock);
  	if (*s == '/') {
  		if (flags & LOOKUP_RCU) {
  			rcu_read_lock();
  			set_root_rcu(nd);
  			nd->seq = nd->root_seq;
  		} else {
  			set_root(nd);
  			path_get(&nd->root);
  		}
  		nd->path = nd->root;
  	} else if (nd->dfd == AT_FDCWD) {
  		if (flags & LOOKUP_RCU) {
  			struct fs_struct *fs = current->fs;
  			unsigned seq;
  
  			rcu_read_lock();
  
  			do {
  				seq = read_seqcount_begin(&fs->seq);
  				nd->path = fs->pwd;
  				nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
  			} while (read_seqcount_retry(&fs->seq, seq));
  		} else {
  			get_fs_pwd(current->fs, &nd->path);
  		}
  	} else {
  		/* Caller must check execute permissions on the starting path component */
  		struct fd f = fdget_raw(nd->dfd);
  		struct dentry *dentry;
  
  		if (!f.file)
  			return ERR_PTR(-EBADF);
  
  		dentry = f.file->f_path.dentry;
  
  		if (*s) {
  			if (!d_can_lookup(dentry)) {
  				fdput(f);
  				return ERR_PTR(-ENOTDIR);
  			}
  		}
  
  		nd->path = f.file->f_path;
  		if (flags & LOOKUP_RCU) {
  			rcu_read_lock();
  			nd->inode = nd->path.dentry->d_inode;
  			nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
  		} else {
  			path_get(&nd->path);
  			nd->inode = nd->path.dentry->d_inode;
  		}
  		fdput(f);
  		return s;
  	}
  
  	nd->inode = nd->path.dentry->d_inode;
  	if (!(flags & LOOKUP_RCU))
  		return s;
  	if (likely(!read_seqcount_retry(&nd->path.dentry->d_seq, nd->seq)))
  		return s;
  	if (!(nd->flags & LOOKUP_ROOT))
  		nd->root.mnt = NULL;
  	rcu_read_unlock();
  	return ERR_PTR(-ECHILD);
  }
  
  static const char *trailing_symlink(struct nameidata *nd)
  {
  	const char *s;
  	int error = may_follow_link(nd);
  	if (unlikely(error))
  		return ERR_PTR(error);
  	nd->flags |= LOOKUP_PARENT;
  	nd->stack[0].name = NULL;
  	s = get_link(nd);
  	return s ? s : "";
  }
  
  static inline int lookup_last(struct nameidata *nd)
  {
  	if (nd->last_type == LAST_NORM && nd->last.name[nd->last.len])
  		nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
  
  	nd->flags &= ~LOOKUP_PARENT;
  	return walk_component(nd,
  			nd->flags & LOOKUP_FOLLOW
  				? nd->depth
  					? WALK_PUT | WALK_GET
  					: WALK_GET
  				: 0);
  }
  
  /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
  static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path)
  {
  	const char *s = path_init(nd, flags);
  	int err;
  
  	if (IS_ERR(s))
  		return PTR_ERR(s);
  	while (!(err = link_path_walk(s, nd))
  		&& ((err = lookup_last(nd)) > 0)) {
  		s = trailing_symlink(nd);
  		if (IS_ERR(s)) {
  			err = PTR_ERR(s);
  			break;
  		}
  	}
  	if (!err)
  		err = complete_walk(nd);
  
  	if (!err && nd->flags & LOOKUP_DIRECTORY)
  		if (!d_can_lookup(nd->path.dentry))
  			err = -ENOTDIR;
  	if (!err) {
  		*path = nd->path;
  		nd->path.mnt = NULL;
  		nd->path.dentry = NULL;
  	}
  	terminate_walk(nd);
  	return err;
  }
  
  static int filename_lookup(int dfd, struct filename *name, unsigned flags,
  			   struct path *path, struct path *root)
  {
  	int retval;
  	struct nameidata nd;
  	if (IS_ERR(name))
  		return PTR_ERR(name);
  	if (unlikely(root)) {
  		nd.root = *root;
  		flags |= LOOKUP_ROOT;
  	}
  	set_nameidata(&nd, dfd, name);
  	retval = path_lookupat(&nd, flags | LOOKUP_RCU, path);
  	if (unlikely(retval == -ECHILD))
  		retval = path_lookupat(&nd, flags, path);
  	if (unlikely(retval == -ESTALE))
  		retval = path_lookupat(&nd, flags | LOOKUP_REVAL, path);
  
  	if (likely(!retval))
  		audit_inode(name, path->dentry, flags & LOOKUP_PARENT);
  	restore_nameidata();
  	putname(name);
  	return retval;
  }
  
  /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */
  static int path_parentat(struct nameidata *nd, unsigned flags,
  				struct path *parent)
  {
  	const char *s = path_init(nd, flags);
  	int err;
  	if (IS_ERR(s))
  		return PTR_ERR(s);
  	err = link_path_walk(s, nd);
  	if (!err)
  		err = complete_walk(nd);
  	if (!err) {
  		*parent = nd->path;
  		nd->path.mnt = NULL;
  		nd->path.dentry = NULL;
  	}
  	terminate_walk(nd);
  	return err;
  }
  
  static struct filename *filename_parentat(int dfd, struct filename *name,
  				unsigned int flags, struct path *parent,
  				struct qstr *last, int *type)
  {
  	int retval;
  	struct nameidata nd;
  
  	if (IS_ERR(name))
  		return name;
  	set_nameidata(&nd, dfd, name);
  	retval = path_parentat(&nd, flags | LOOKUP_RCU, parent);
  	if (unlikely(retval == -ECHILD))
  		retval = path_parentat(&nd, flags, parent);
  	if (unlikely(retval == -ESTALE))
  		retval = path_parentat(&nd, flags | LOOKUP_REVAL, parent);
  	if (likely(!retval)) {
  		*last = nd.last;
  		*type = nd.last_type;
  		audit_inode(name, parent->dentry, LOOKUP_PARENT);
  	} else {
  		putname(name);
  		name = ERR_PTR(retval);
  	}
  	restore_nameidata();
  	return name;
  }
  
  /* does lookup, returns the object with parent locked */
  struct dentry *kern_path_locked(const char *name, struct path *path)
  {
  	struct filename *filename;
  	struct dentry *d;
  	struct qstr last;
  	int type;
  
  	filename = filename_parentat(AT_FDCWD, getname_kernel(name), 0, path,
  				    &last, &type);
  	if (IS_ERR(filename))
  		return ERR_CAST(filename);
  	if (unlikely(type != LAST_NORM)) {
  		path_put(path);
  		putname(filename);
  		return ERR_PTR(-EINVAL);
  	}
  	mutex_lock_nested(&path->dentry->d_inode->i_mutex, I_MUTEX_PARENT);
  	d = __lookup_hash(&last, path->dentry, 0);
  	if (IS_ERR(d)) {
  		mutex_unlock(&path->dentry->d_inode->i_mutex);
  		path_put(path);
  	}
  	putname(filename);
  	return d;
  }
  
  int kern_path(const char *name, unsigned int flags, struct path *path)
  {
  	return filename_lookup(AT_FDCWD, getname_kernel(name),
  			       flags, path, NULL);
  }
  EXPORT_SYMBOL(kern_path);
  
  /**
   * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair
   * @dentry:  pointer to dentry of the base directory
   * @mnt: pointer to vfs mount of the base directory
   * @name: pointer to file name
   * @flags: lookup flags
   * @path: pointer to struct path to fill
   */
  int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt,
  		    const char *name, unsigned int flags,
  		    struct path *path)
  {
  	struct path root = {.mnt = mnt, .dentry = dentry};
  	/* the first argument of filename_lookup() is ignored with root */
  	return filename_lookup(AT_FDCWD, getname_kernel(name),
  			       flags , path, &root);
  }
  EXPORT_SYMBOL(vfs_path_lookup);
  
  /**
   * lookup_one_len - filesystem helper to lookup single pathname component
   * @name:	pathname component to lookup
   * @base:	base directory to lookup from
   * @len:	maximum length @len should be interpreted to
   *
   * Note that this routine is purely a helper for filesystem usage and should
   * not be called by generic code.
   */
  struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
  {
  	struct qstr this;
  	unsigned int c;
  	int err;
  
  	WARN_ON_ONCE(!mutex_is_locked(&base->d_inode->i_mutex));
  
  	this.name = name;
  	this.len = len;
  	this.hash = full_name_hash(name, len);
  	if (!len)
  		return ERR_PTR(-EACCES);
  
  	if (unlikely(name[0] == '.')) {
  		if (len < 2 || (len == 2 && name[1] == '.'))
  			return ERR_PTR(-EACCES);
  	}
  
  	while (len--) {
  		c = *(const unsigned char *)name++;
  		if (c == '/' || c == '\0')
  			return ERR_PTR(-EACCES);
  	}
  	/*
  	 * See if the low-level filesystem might want
  	 * to use its own hash..
  	 */
  	if (base->d_flags & DCACHE_OP_HASH) {
  		int err = base->d_op->d_hash(base, &this);
  		if (err < 0)
  			return ERR_PTR(err);
  	}
  
  	err = inode_permission(base->d_inode, MAY_EXEC);
  	if (err)
  		return ERR_PTR(err);
  
  	return __lookup_hash(&this, base, 0);
  }
  EXPORT_SYMBOL(lookup_one_len);
  
  int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
  		 struct path *path, int *empty)
  {
  	return filename_lookup(dfd, getname_flags(name, flags, empty),
  			       flags, path, NULL);
  }
  EXPORT_SYMBOL(user_path_at_empty);
  
  /*
   * NB: most callers don't do anything directly with the reference to the
   *     to struct filename, but the nd->last pointer points into the name string
   *     allocated by getname. So we must hold the reference to it until all
   *     path-walking is complete.
   */
  static inline struct filename *
  user_path_parent(int dfd, const char __user *path,
  		 struct path *parent,
  		 struct qstr *last,
  		 int *type,
  		 unsigned int flags)
  {
  	/* only LOOKUP_REVAL is allowed in extra flags */
  	return filename_parentat(dfd, getname(path), flags & LOOKUP_REVAL,
  				 parent, last, type);
  }
  
  /**
   * mountpoint_last - look up last component for umount
   * @nd:   pathwalk nameidata - currently pointing at parent directory of "last"
   * @path: pointer to container for result
   *
   * This is a special lookup_last function just for umount. In this case, we
   * need to resolve the path without doing any revalidation.
   *
   * The nameidata should be the result of doing a LOOKUP_PARENT pathwalk. Since
   * mountpoints are always pinned in the dcache, their ancestors are too. Thus,
   * in almost all cases, this lookup will be served out of the dcache. The only
   * cases where it won't are if nd->last refers to a symlink or the path is
   * bogus and it doesn't exist.
   *
   * Returns:
   * -error: if there was an error during lookup. This includes -ENOENT if the
   *         lookup found a negative dentry. The nd->path reference will also be
   *         put in this case.
   *
   * 0:      if we successfully resolved nd->path and found it to not to be a
   *         symlink that needs to be followed. "path" will also be populated.
   *         The nd->path reference will also be put.
   *
   * 1:      if we successfully resolved nd->last and found it to be a symlink
   *         that needs to be followed. "path" will be populated with the path
   *         to the link, and nd->path will *not* be put.
   */
  static int
  mountpoint_last(struct nameidata *nd, struct path *path)
  {
  	int error = 0;
  	struct dentry *dentry;
  	struct dentry *dir = nd->path.dentry;
  
  	/* If we're in rcuwalk, drop out of it to handle last component */
  	if (nd->flags & LOOKUP_RCU) {
  		if (unlazy_walk(nd, NULL, 0))
  			return -ECHILD;
  	}
  
  	nd->flags &= ~LOOKUP_PARENT;
  
  	if (unlikely(nd->last_type != LAST_NORM)) {
  		error = handle_dots(nd, nd->last_type);
  		if (error)
  			return error;
  		dentry = dget(nd->path.dentry);
  		goto done;
  	}
  
  	mutex_lock(&dir->d_inode->i_mutex);
  	dentry = d_lookup(dir, &nd->last);
  	if (!dentry) {
  		/*
  		 * No cached dentry. Mounted dentries are pinned in the cache,
  		 * so that means that this dentry is probably a symlink or the
  		 * path doesn't actually point to a mounted dentry.
  		 */
  		dentry = d_alloc(dir, &nd->last);
  		if (!dentry) {
  			mutex_unlock(&dir->d_inode->i_mutex);
  			return -ENOMEM;
  		}
  		dentry = lookup_real(dir->d_inode, dentry, nd->flags);
  		if (IS_ERR(dentry)) {
  			mutex_unlock(&dir->d_inode->i_mutex);
  			return PTR_ERR(dentry);
  		}
  	}
  	mutex_unlock(&dir->d_inode->i_mutex);
  
  done:
  	if (d_is_negative(dentry)) {
  		dput(dentry);
  		return -ENOENT;
  	}
  	if (nd->depth)
  		put_link(nd);
  	path->dentry = dentry;
  	path->mnt = nd->path.mnt;
  	error = should_follow_link(nd, path, nd->flags & LOOKUP_FOLLOW,
  				   d_backing_inode(dentry), 0);
  	if (unlikely(error))
  		return error;
  	mntget(path->mnt);
  	follow_mount(path);
  	return 0;
  }
  
  /**
   * path_mountpoint - look up a path to be umounted
   * @nameidata:	lookup context
   * @flags:	lookup flags
   * @path:	pointer to container for result
   *
   * Look up the given name, but don't attempt to revalidate the last component.
   * Returns 0 and "path" will be valid on success; Returns error otherwise.
   */
  static int
  path_mountpoint(struct nameidata *nd, unsigned flags, struct path *path)
  {
  	const char *s = path_init(nd, flags);
  	int err;
  	if (IS_ERR(s))
  		return PTR_ERR(s);
  	while (!(err = link_path_walk(s, nd)) &&
  		(err = mountpoint_last(nd, path)) > 0) {
  		s = trailing_symlink(nd);
  		if (IS_ERR(s)) {
  			err = PTR_ERR(s);
  			break;
  		}
  	}
  	terminate_walk(nd);
  	return err;
  }
  
  static int
  filename_mountpoint(int dfd, struct filename *name, struct path *path,
  			unsigned int flags)
  {
  	struct nameidata nd;
  	int error;
  	if (IS_ERR(name))
  		return PTR_ERR(name);
  	set_nameidata(&nd, dfd, name);
  	error = path_mountpoint(&nd, flags | LOOKUP_RCU, path);
  	if (unlikely(error == -ECHILD))
  		error = path_mountpoint(&nd, flags, path);
  	if (unlikely(error == -ESTALE))
  		error = path_mountpoint(&nd, flags | LOOKUP_REVAL, path);
  	if (likely(!error))
  		audit_inode(name, path->dentry, 0);
  	restore_nameidata();
  	putname(name);
  	return error;
  }
  
  /**
   * user_path_mountpoint_at - lookup a path from userland in order to umount it
   * @dfd:	directory file descriptor
   * @name:	pathname from userland
   * @flags:	lookup flags
   * @path:	pointer to container to hold result
   *
   * A umount is a special case for path walking. We're not actually interested
   * in the inode in this situation, and ESTALE errors can be a problem. We
   * simply want track down the dentry and vfsmount attached at the mountpoint
   * and avoid revalidating the last component.
   *
   * Returns 0 and populates "path" on success.
   */
  int
  user_path_mountpoint_at(int dfd, const char __user *name, unsigned int flags,
  			struct path *path)
  {
  	return filename_mountpoint(dfd, getname(name), path, flags);
  }
  
  int
  kern_path_mountpoint(int dfd, const char *name, struct path *path,
  			unsigned int flags)
  {
  	return filename_mountpoint(dfd, getname_kernel(name), path, flags);
  }
  EXPORT_SYMBOL(kern_path_mountpoint);
  
  int __check_sticky(struct inode *dir, struct inode *inode)
  {
  	kuid_t fsuid = current_fsuid();
  
  	if (uid_eq(inode->i_uid, fsuid))
  		return 0;
  	if (uid_eq(dir->i_uid, fsuid))
  		return 0;
  	return !capable_wrt_inode_uidgid(inode, CAP_FOWNER);
  }
  EXPORT_SYMBOL(__check_sticky);
  
  /*
   *	Check whether we can remove a link victim from directory dir, check
   *  whether the type of victim is right.
   *  1. We can't do it if dir is read-only (done in permission())
   *  2. We should have write and exec permissions on dir
   *  3. We can't remove anything from append-only dir
   *  4. We can't do anything with immutable dir (done in permission())
   *  5. If the sticky bit on dir is set we should either
   *	a. be owner of dir, or
   *	b. be owner of victim, or
   *	c. have CAP_FOWNER capability
   *  6. If the victim is append-only or immutable we can't do antyhing with
   *     links pointing to it.
   *  7. If we were asked to remove a directory and victim isn't one - ENOTDIR.
   *  8. If we were asked to remove a non-directory and victim isn't one - EISDIR.
   *  9. We can't remove a root or mountpoint.
   * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
   *     nfs_async_unlink().
   */
  static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
  {
  	struct inode *inode = d_backing_inode(victim);
  	int error;
  
  	if (d_is_negative(victim))
  		return -ENOENT;
  	BUG_ON(!inode);
  
  	BUG_ON(victim->d_parent->d_inode != dir);
  	audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE);
  
  	error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
  	if (error)
  		return error;
  	if (IS_APPEND(dir))
  		return -EPERM;
  
  	if (check_sticky(dir, inode) || IS_APPEND(inode) ||
  	    IS_IMMUTABLE(inode) || IS_SWAPFILE(inode))
  		return -EPERM;
  	if (isdir) {
  		if (!d_is_dir(victim))
  			return -ENOTDIR;
  		if (IS_ROOT(victim))
  			return -EBUSY;
  	} else if (d_is_dir(victim))
  		return -EISDIR;
  	if (IS_DEADDIR(dir))
  		return -ENOENT;
  	if (victim->d_flags & DCACHE_NFSFS_RENAMED)
  		return -EBUSY;
  	return 0;
  }
  
  /*	Check whether we can create an object with dentry child in directory
   *  dir.
   *  1. We can't do it if child already exists (open has special treatment for
   *     this case, but since we are inlined it's OK)
   *  2. We can't do it if dir is read-only (done in permission())
   *  3. We should have write and exec permissions on dir
   *  4. We can't do it if dir is immutable (done in permission())
   */
  static inline int may_create(struct inode *dir, struct dentry *child)
  {
  	audit_inode_child(dir, child, AUDIT_TYPE_CHILD_CREATE);
  	if (child->d_inode)
  		return -EEXIST;
  	if (IS_DEADDIR(dir))
  		return -ENOENT;
  	return inode_permission(dir, MAY_WRITE | MAY_EXEC);
  }
  
  /*
   * p1 and p2 should be directories on the same fs.
   */
  struct dentry *lock_rename(struct dentry *p1, struct dentry *p2)
  {
  	struct dentry *p;
  
  	if (p1 == p2) {
  		mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
  		return NULL;
  	}
  
  	mutex_lock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
  
  	p = d_ancestor(p2, p1);
  	if (p) {
  		mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT);
  		mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_CHILD);
  		return p;
  	}
  
  	p = d_ancestor(p1, p2);
  	if (p) {
  		mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
  		mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD);
  		return p;
  	}
  
  	mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
  	mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT2);
  	return NULL;
  }
  EXPORT_SYMBOL(lock_rename);
  
  void unlock_rename(struct dentry *p1, struct dentry *p2)
  {
  	mutex_unlock(&p1->d_inode->i_mutex);
  	if (p1 != p2) {
  		mutex_unlock(&p2->d_inode->i_mutex);
  		mutex_unlock(&p1->d_inode->i_sb->s_vfs_rename_mutex);
  	}
  }
  EXPORT_SYMBOL(unlock_rename);
  
  int vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
  		bool want_excl)
  {
  	int error = may_create(dir, dentry);
  	if (error)
  		return error;
  
  	if (!dir->i_op->create)
  		return -EACCES;	/* shouldn't it be ENOSYS? */
  	mode &= S_IALLUGO;
  	mode |= S_IFREG;
  	error = security_inode_create(dir, dentry, mode);
  	if (error)
  		return error;
  	error = dir->i_op->create(dir, dentry, mode, want_excl);
  	if (!error)
  		fsnotify_create(dir, dentry);
  	return error;
  }
  EXPORT_SYMBOL(vfs_create);
  
  static int may_open(struct path *path, int acc_mode, int flag)
  {
  	struct dentry *dentry = path->dentry;
  	struct inode *inode = dentry->d_inode;
  	int error;
  
  	/* O_PATH? */
  	if (!acc_mode)
  		return 0;
  
  	if (!inode)
  		return -ENOENT;
  
  	switch (inode->i_mode & S_IFMT) {
  	case S_IFLNK:
  		return -ELOOP;
  	case S_IFDIR:
  		if (acc_mode & MAY_WRITE)
  			return -EISDIR;
  		break;
  	case S_IFBLK:
  	case S_IFCHR:
  		if (path->mnt->mnt_flags & MNT_NODEV)
  			return -EACCES;
  		/*FALLTHRU*/
  	case S_IFIFO:
  	case S_IFSOCK:
  		flag &= ~O_TRUNC;
  		break;
  	}
  
  	error = inode_permission(inode, acc_mode);
  	if (error)
  		return error;
  
  	/*
  	 * An append-only file must be opened in append mode for writing.
  	 */
  	if (IS_APPEND(inode)) {
  		if  ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
  			return -EPERM;
  		if (flag & O_TRUNC)
  			return -EPERM;
  	}
  
  	/* O_NOATIME can only be set by the owner or superuser */
  	if (flag & O_NOATIME && !inode_owner_or_capable(inode))
  		return -EPERM;
  
  	return 0;
  }
  
  static int handle_truncate(struct file *filp)
  {
  	struct path *path = &filp->f_path;
  	struct inode *inode = path->dentry->d_inode;
  	int error = get_write_access(inode);
  	if (error)
  		return error;
  	/*
  	 * Refuse to truncate files with mandatory locks held on them.
  	 */
  	error = locks_verify_locked(filp);
  	if (!error)
  		error = security_path_truncate(path);
  	if (!error) {
  		error = do_truncate(path->dentry, 0,
  				    ATTR_MTIME|ATTR_CTIME|ATTR_OPEN,
  				    filp);
  	}
  	put_write_access(inode);
  	return error;
  }
  
  static inline int open_to_namei_flags(int flag)
  {
  	if ((flag & O_ACCMODE) == 3)
  		flag--;
  	return flag;
  }
  
  static int may_o_create(struct path *dir, struct dentry *dentry, umode_t mode)
  {
  	int error = security_path_mknod(dir, dentry, mode, 0);
  	if (error)
  		return error;
  
  	error = inode_permission(dir->dentry->d_inode, MAY_WRITE | MAY_EXEC);
  	if (error)
  		return error;
  
  	return security_inode_create(dir->dentry->d_inode, dentry, mode);
  }
  
  /*
   * Attempt to atomically look up, create and open a file from a negative
   * dentry.
   *
   * Returns 0 if successful.  The file will have been created and attached to
   * @file by the filesystem calling finish_open().
   *
   * Returns 1 if the file was looked up only or didn't need creating.  The
   * caller will need to perform the open themselves.  @path will have been
   * updated to point to the new dentry.  This may be negative.
   *
   * Returns an error code otherwise.
   */
  static int atomic_open(struct nameidata *nd, struct dentry *dentry,
  			struct path *path, struct file *file,
  			const struct open_flags *op,
  			bool got_write, bool need_lookup,
  			int *opened)
  {
  	struct inode *dir =  nd->path.dentry->d_inode;
  	unsigned open_flag = open_to_namei_flags(op->open_flag);
  	umode_t mode;
  	int error;
  	int acc_mode;
  	int create_error = 0;
  	struct dentry *const DENTRY_NOT_SET = (void *) -1UL;
  	bool excl;
  
  	BUG_ON(dentry->d_inode);
  
  	/* Don't create child dentry for a dead directory. */
  	if (unlikely(IS_DEADDIR(dir))) {
  		error = -ENOENT;
  		goto out;
  	}
  
  	mode = op->mode;
  	if ((open_flag & O_CREAT) && !IS_POSIXACL(dir))
  		mode &= ~current_umask();
  
  	excl = (open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT);
  	if (excl)
  		open_flag &= ~O_TRUNC;
  
  	/*
  	 * Checking write permission is tricky, bacuse we don't know if we are
  	 * going to actually need it: O_CREAT opens should work as long as the
  	 * file exists.  But checking existence breaks atomicity.  The trick is
  	 * to check access and if not granted clear O_CREAT from the flags.
  	 *
  	 * Another problem is returing the "right" error value (e.g. for an
  	 * O_EXCL open we want to return EEXIST not EROFS).
  	 */
  	if (((open_flag & (O_CREAT | O_TRUNC)) ||
  	    (open_flag & O_ACCMODE) != O_RDONLY) && unlikely(!got_write)) {
  		if (!(open_flag & O_CREAT)) {
  			/*
  			 * No O_CREATE -> atomicity not a requirement -> fall
  			 * back to lookup + open
  			 */
  			goto no_open;
  		} else if (open_flag & (O_EXCL | O_TRUNC)) {
  			/* Fall back and fail with the right error */
  			create_error = -EROFS;
  			goto no_open;
  		} else {
  			/* No side effects, safe to clear O_CREAT */
  			create_error = -EROFS;
  			open_flag &= ~O_CREAT;
  		}
  	}
  
  	if (open_flag & O_CREAT) {
  		error = may_o_create(&nd->path, dentry, mode);
  		if (error) {
  			create_error = error;
  			if (open_flag & O_EXCL)
  				goto no_open;
  			open_flag &= ~O_CREAT;
  		}
  	}
  
  	if (nd->flags & LOOKUP_DIRECTORY)
  		open_flag |= O_DIRECTORY;
  
  	file->f_path.dentry = DENTRY_NOT_SET;
  	file->f_path.mnt = nd->path.mnt;
  	error = dir->i_op->atomic_open(dir, dentry, file, open_flag, mode,
  				      opened);
  	if (error < 0) {
  		if (create_error && error == -ENOENT)
  			error = create_error;
  		goto out;
  	}
  
  	if (error) {	/* returned 1, that is */
  		if (WARN_ON(file->f_path.dentry == DENTRY_NOT_SET)) {
  			error = -EIO;
  			goto out;
  		}
  		if (file->f_path.dentry) {
  			dput(dentry);
  			dentry = file->f_path.dentry;
  		}
  		if (*opened & FILE_CREATED)
  			fsnotify_create(dir, dentry);
  		if (!dentry->d_inode) {
  			WARN_ON(*opened & FILE_CREATED);
  			if (create_error) {
  				error = create_error;
  				goto out;
  			}
  		} else {
  			if (excl && !(*opened & FILE_CREATED)) {
  				error = -EEXIST;
  				goto out;
  			}
  		}
  		goto looked_up;
  	}
  
  	/*
  	 * We didn't have the inode before the open, so check open permission
  	 * here.
  	 */
  	acc_mode = op->acc_mode;
  	if (*opened & FILE_CREATED) {
  		WARN_ON(!(open_flag & O_CREAT));
  		fsnotify_create(dir, dentry);
  		acc_mode = MAY_OPEN;
  	}
  	error = may_open(&file->f_path, acc_mode, open_flag);
  	if (error)
  		fput(file);
  
  out:
  	dput(dentry);
  	return error;
  
  no_open:
  	if (need_lookup) {
  		dentry = lookup_real(dir, dentry, nd->flags);
  		if (IS_ERR(dentry))
  			return PTR_ERR(dentry);
  
  		if (create_error) {
  			int open_flag = op->open_flag;
  
  			error = create_error;
  			if ((open_flag & O_EXCL)) {
  				if (!dentry->d_inode)
  					goto out;
  			} else if (!dentry->d_inode) {
  				goto out;
  			} else if ((open_flag & O_TRUNC) &&
  				   d_is_reg(dentry)) {
  				goto out;
  			}
  			/* will fail later, go on to get the right error */
  		}
  	}
  looked_up:
  	path->dentry = dentry;
  	path->mnt = nd->path.mnt;
  	return 1;
  }
  
  /*
   * Look up and maybe create and open the last component.
   *
   * Must be called with i_mutex held on parent.
   *
   * Returns 0 if the file was successfully atomically created (if necessary) and
   * opened.  In this case the file will be returned attached to @file.
   *
   * Returns 1 if the file was not completely opened at this time, though lookups
   * and creations will have been performed and the dentry returned in @path will
   * be positive upon return if O_CREAT was specified.  If O_CREAT wasn't
   * specified then a negative dentry may be returned.
   *
   * An error code is returned otherwise.
   *
   * FILE_CREATE will be set in @*opened if the dentry was created and will be
   * cleared otherwise prior to returning.
   */
  static int lookup_open(struct nameidata *nd, struct path *path,
  			struct file *file,
  			const struct open_flags *op,
  			bool got_write, int *opened)
  {
  	struct dentry *dir = nd->path.dentry;
  	struct inode *dir_inode = dir->d_inode;
  	struct dentry *dentry;
  	int error;
  	bool need_lookup;
  
  	*opened &= ~FILE_CREATED;
  	dentry = lookup_dcache(&nd->last, dir, nd->flags, &need_lookup);
  	if (IS_ERR(dentry))
  		return PTR_ERR(dentry);
  
  	/* Cached positive dentry: will open in f_op->open */
  	if (!need_lookup && dentry->d_inode)
  		goto out_no_open;
  
  	if ((nd->flags & LOOKUP_OPEN) && dir_inode->i_op->atomic_open) {
  		return atomic_open(nd, dentry, path, file, op, got_write,
  				   need_lookup, opened);
  	}
  
  	if (need_lookup) {
  		BUG_ON(dentry->d_inode);
  
  		dentry = lookup_real(dir_inode, dentry, nd->flags);
  		if (IS_ERR(dentry))
  			return PTR_ERR(dentry);
  	}
  
  	/* Negative dentry, just create the file */
  	if (!dentry->d_inode && (op->open_flag & O_CREAT)) {
  		umode_t mode = op->mode;
  		if (!IS_POSIXACL(dir->d_inode))
  			mode &= ~current_umask();
  		/*
  		 * This write is needed to ensure that a
  		 * rw->ro transition does not occur between
  		 * the time when the file is created and when
  		 * a permanent write count is taken through
  		 * the 'struct file' in finish_open().
  		 */
  		if (!got_write) {
  			error = -EROFS;
  			goto out_dput;
  		}
  		*opened |= FILE_CREATED;
  		error = security_path_mknod(&nd->path, dentry, mode, 0);
  		if (error)
  			goto out_dput;
  		error = vfs_create(dir->d_inode, dentry, mode,
  				   nd->flags & LOOKUP_EXCL);
  		if (error)
  			goto out_dput;
  	}
  out_no_open:
  	path->dentry = dentry;
  	path->mnt = nd->path.mnt;
  	return 1;
  
  out_dput:
  	dput(dentry);
  	return error;
  }
  
  /*
   * Handle the last step of open()
   */
  static int do_last(struct nameidata *nd,
  		   struct file *file, const struct open_flags *op,
  		   int *opened)
  {
  	struct dentry *dir = nd->path.dentry;
  	int open_flag = op->open_flag;
  	bool will_truncate = (open_flag & O_TRUNC) != 0;
  	bool got_write = false;
  	int acc_mode = op->acc_mode;
  	unsigned seq;
  	struct inode *inode;
  	struct path save_parent = { .dentry = NULL, .mnt = NULL };
  	struct path path;
  	bool retried = false;
  	int error;
  
  	nd->flags &= ~LOOKUP_PARENT;
  	nd->flags |= op->intent;
  
  	if (nd->last_type != LAST_NORM) {
  		error = handle_dots(nd, nd->last_type);
  		if (unlikely(error))
  			return error;
  		goto finish_open;
  	}
  
  	if (!(open_flag & O_CREAT)) {
  		if (nd->last.name[nd->last.len])
  			nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
  		/* we _can_ be in RCU mode here */
  		error = lookup_fast(nd, &path, &inode, &seq);
  		if (likely(!error))
  			goto finish_lookup;
  
  		if (error < 0)
  			return error;
  
  		BUG_ON(nd->inode != dir->d_inode);
  	} else {
  		/* create side of things */
  		/*
  		 * This will *only* deal with leaving RCU mode - LOOKUP_JUMPED
  		 * has been cleared when we got to the last component we are
  		 * about to look up
  		 */
  		error = complete_walk(nd);
  		if (error)
  			return error;
  
  		audit_inode(nd->name, dir, LOOKUP_PARENT);
  		/* trailing slashes? */
  		if (unlikely(nd->last.name[nd->last.len]))
  			return -EISDIR;
  	}
  
  retry_lookup:
  	if (op->open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) {
  		error = mnt_want_write(nd->path.mnt);
  		if (!error)
  			got_write = true;
  		/*
  		 * do _not_ fail yet - we might not need that or fail with
  		 * a different error; let lookup_open() decide; we'll be
  		 * dropping this one anyway.
  		 */
  	}
  	mutex_lock(&dir->d_inode->i_mutex);
  	error = lookup_open(nd, &path, file, op, got_write, opened);
  	mutex_unlock(&dir->d_inode->i_mutex);
  
  	if (error <= 0) {
  		if (error)
  			goto out;
  
  		if ((*opened & FILE_CREATED) ||
  		    !S_ISREG(file_inode(file)->i_mode))
  			will_truncate = false;
  
  		audit_inode(nd->name, file->f_path.dentry, 0);
  		goto opened;
  	}
  
  	if (*opened & FILE_CREATED) {
  		/* Don't check for write permission, don't truncate */
  		open_flag &= ~O_TRUNC;
  		will_truncate = false;
  		acc_mode = MAY_OPEN;
  		path_to_nameidata(&path, nd);
  		goto finish_open_created;
  	}
  
  	/*
  	 * create/update audit record if it already exists.
  	 */
  	if (d_is_positive(path.dentry))
  		audit_inode(nd->name, path.dentry, 0);
  
  	/*
  	 * If atomic_open() acquired write access it is dropped now due to
  	 * possible mount and symlink following (this might be optimized away if
  	 * necessary...)
  	 */
  	if (got_write) {
  		mnt_drop_write(nd->path.mnt);
  		got_write = false;
  	}
  
  	if (unlikely((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT))) {
  		path_to_nameidata(&path, nd);
  		return -EEXIST;
  	}
  
  	error = follow_managed(&path, nd);
  	if (unlikely(error < 0))
  		return error;
  
  	BUG_ON(nd->flags & LOOKUP_RCU);
  	inode = d_backing_inode(path.dentry);
  	seq = 0;	/* out of RCU mode, so the value doesn't matter */
  	if (unlikely(d_is_negative(path.dentry))) {
  		path_to_nameidata(&path, nd);
  		return -ENOENT;
  	}
  finish_lookup:
  	if (nd->depth)
  		put_link(nd);
  	error = should_follow_link(nd, &path, nd->flags & LOOKUP_FOLLOW,
  				   inode, seq);
  	if (unlikely(error))
  		return error;
  
  	if (unlikely(d_is_symlink(path.dentry)) && !(open_flag & O_PATH)) {
  		path_to_nameidata(&path, nd);
  		return -ELOOP;
  	}
  
  	if ((nd->flags & LOOKUP_RCU) || nd->path.mnt != path.mnt) {
  		path_to_nameidata(&path, nd);
  	} else {
  		save_parent.dentry = nd->path.dentry;
  		save_parent.mnt = mntget(path.mnt);
  		nd->path.dentry = path.dentry;
  
  	}
  	nd->inode = inode;
  	nd->seq = seq;
  	/* Why this, you ask?  _Now_ we might have grown LOOKUP_JUMPED... */
  finish_open:
  	error = complete_walk(nd);
  	if (error) {
  		path_put(&save_parent);
  		return error;
  	}
  	audit_inode(nd->name, nd->path.dentry, 0);
  	error = -EISDIR;
  	if ((open_flag & O_CREAT) && d_is_dir(nd->path.dentry))
  		goto out;
  	error = -ENOTDIR;
  	if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry))
  		goto out;
  	if (!d_is_reg(nd->path.dentry))
  		will_truncate = false;
  
  	if (will_truncate) {
  		error = mnt_want_write(nd->path.mnt);
  		if (error)
  			goto out;
  		got_write = true;
  	}
  finish_open_created:
  	error = may_open(&nd->path, acc_mode, open_flag);
  	if (error)
  		goto out;
  
  	BUG_ON(*opened & FILE_OPENED); /* once it's opened, it's opened */
  	error = vfs_open(&nd->path, file, current_cred());
  	if (!error) {
  		*opened |= FILE_OPENED;
  	} else {
  		if (error == -EOPENSTALE)
  			goto stale_open;
  		goto out;
  	}
  opened:
  	error = open_check_o_direct(file);
  	if (error)
  		goto exit_fput;
  	error = ima_file_check(file, op->acc_mode, *opened);
  	if (error)
  		goto exit_fput;
  
  	if (will_truncate) {
  		error = handle_truncate(file);
  		if (error)
  			goto exit_fput;
  	}
  out:
  	if (got_write)
  		mnt_drop_write(nd->path.mnt);
  	path_put(&save_parent);
  	return error;
  
  exit_fput:
  	fput(file);
  	goto out;
  
  stale_open:
  	/* If no saved parent or already retried then can't retry */
  	if (!save_parent.dentry || retried)
  		goto out;
  
  	BUG_ON(save_parent.dentry != dir);
  	path_put(&nd->path);
  	nd->path = save_parent;
  	nd->inode = dir->d_inode;
  	save_parent.mnt = NULL;
  	save_parent.dentry = NULL;
  	if (got_write) {
  		mnt_drop_write(nd->path.mnt);
  		got_write = false;
  	}
  	retried = true;
  	goto retry_lookup;
  }
  
  static int do_tmpfile(struct nameidata *nd, unsigned flags,
  		const struct open_flags *op,
  		struct file *file, int *opened)
  {
  	static const struct qstr name = QSTR_INIT("/", 1);
  	struct dentry *child;
  	struct inode *dir;
  	struct path path;
  	int error = path_lookupat(nd, flags | LOOKUP_DIRECTORY, &path);
  	if (unlikely(error))
  		return error;
  	error = mnt_want_write(path.mnt);
  	if (unlikely(error))
  		goto out;
  	dir = path.dentry->d_inode;
  	/* we want directory to be writable */
  	error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
  	if (error)
  		goto out2;
  	if (!dir->i_op->tmpfile) {
  		error = -EOPNOTSUPP;
  		goto out2;
  	}
  	child = d_alloc(path.dentry, &name);
  	if (unlikely(!child)) {
  		error = -ENOMEM;
  		goto out2;
  	}
  	dput(path.dentry);
  	path.dentry = child;
  	error = dir->i_op->tmpfile(dir, child, op->mode);
  	if (error)
  		goto out2;
  	audit_inode(nd->name, child, 0);
  	/* Don't check for other permissions, the inode was just created */
  	error = may_open(&path, MAY_OPEN, op->open_flag);
  	if (error)
  		goto out2;
  	file->f_path.mnt = path.mnt;
  	error = finish_open(file, child, NULL, opened);
  	if (error)
  		goto out2;
  	error = open_check_o_direct(file);
  	if (error) {
  		fput(file);
  	} else if (!(op->open_flag & O_EXCL)) {
  		struct inode *inode = file_inode(file);
  		spin_lock(&inode->i_lock);
  		inode->i_state |= I_LINKABLE;
  		spin_unlock(&inode->i_lock);
  	}
  out2:
  	mnt_drop_write(path.mnt);
  out:
  	path_put(&path);
  	return error;
  }
  
  static struct file *path_openat(struct nameidata *nd,
  			const struct open_flags *op, unsigned flags)
  {
  	const char *s;
  	struct file *file;
  	int opened = 0;
  	int error;
  
  	file = get_empty_filp();
  	if (IS_ERR(file))
  		return file;
  
  	file->f_flags = op->open_flag;
  
  	if (unlikely(file->f_flags & __O_TMPFILE)) {
  		error = do_tmpfile(nd, flags, op, file, &opened);
  		goto out2;
  	}
  
  	s = path_init(nd, flags);
  	if (IS_ERR(s)) {
  		put_filp(file);
  		return ERR_CAST(s);
  	}
  	while (!(error = link_path_walk(s, nd)) &&
  		(error = do_last(nd, file, op, &opened)) > 0) {
  		nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL);
  		s = trailing_symlink(nd);
  		if (IS_ERR(s)) {
  			error = PTR_ERR(s);
  			break;
  		}
  	}
  	terminate_walk(nd);
  out2:
  	if (!(opened & FILE_OPENED)) {
  		BUG_ON(!error);
  		put_filp(file);
  	}
  	if (unlikely(error)) {
  		if (error == -EOPENSTALE) {
  			if (flags & LOOKUP_RCU)
  				error = -ECHILD;
  			else
  				error = -ESTALE;
  		}
  		file = ERR_PTR(error);
  	}
  	return file;
  }
  
  struct file *do_filp_open(int dfd, struct filename *pathname,
  		const struct open_flags *op)
  {
  	struct nameidata nd;
  	int flags = op->lookup_flags;
  	struct file *filp;
  
  	set_nameidata(&nd, dfd, pathname);
  	filp = path_openat(&nd, op, flags | LOOKUP_RCU);
  	if (unlikely(filp == ERR_PTR(-ECHILD)))
  		filp = path_openat(&nd, op, flags);
  	if (unlikely(filp == ERR_PTR(-ESTALE)))
  		filp = path_openat(&nd, op, flags | LOOKUP_REVAL);
  	restore_nameidata();
  	return filp;
  }
  
  struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
  		const char *name, const struct open_flags *op)
  {
  	struct nameidata nd;
  	struct file *file;
  	struct filename *filename;
  	int flags = op->lookup_flags | LOOKUP_ROOT;
  
  	nd.root.mnt = mnt;
  	nd.root.dentry = dentry;
  
  	if (d_is_symlink(dentry) && op->intent & LOOKUP_OPEN)
  		return ERR_PTR(-ELOOP);
  
  	filename = getname_kernel(name);
  	if (unlikely(IS_ERR(filename)))
  		return ERR_CAST(filename);
  
  	set_nameidata(&nd, -1, filename);
  	file = path_openat(&nd, op, flags | LOOKUP_RCU);
  	if (unlikely(file == ERR_PTR(-ECHILD)))
  		file = path_openat(&nd, op, flags);
  	if (unlikely(file == ERR_PTR(-ESTALE)))
  		file = path_openat(&nd, op, flags | LOOKUP_REVAL);
  	restore_nameidata();
  	putname(filename);
  	return file;
  }
  
  static struct dentry *filename_create(int dfd, struct filename *name,
  				struct path *path, unsigned int lookup_flags)
  {
  	struct dentry *dentry = ERR_PTR(-EEXIST);
  	struct qstr last;
  	int type;
  	int err2;
  	int error;
  	bool is_dir = (lookup_flags & LOOKUP_DIRECTORY);
  
  	/*
  	 * Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any
  	 * other flags passed in are ignored!
  	 */
  	lookup_flags &= LOOKUP_REVAL;
  
  	name = filename_parentat(dfd, name, lookup_flags, path, &last, &type);
  	if (IS_ERR(name))
  		return ERR_CAST(name);
  
  	/*
  	 * Yucky last component or no last component at all?
  	 * (foo/., foo/.., /////)
  	 */
  	if (unlikely(type != LAST_NORM))
  		goto out;
  
  	/* don't fail immediately if it's r/o, at least try to report other errors */
  	err2 = mnt_want_write(path->mnt);
  	/*
  	 * Do the final lookup.
  	 */
  	lookup_flags |= LOOKUP_CREATE | LOOKUP_EXCL;
  	mutex_lock_nested(&path->dentry->d_inode->i_mutex, I_MUTEX_PARENT);
  	dentry = __lookup_hash(&last, path->dentry, lookup_flags);
  	if (IS_ERR(dentry))
  		goto unlock;
  
  	error = -EEXIST;
  	if (d_is_positive(dentry))
  		goto fail;
  
  	/*
  	 * Special case - lookup gave negative, but... we had foo/bar/
  	 * From the vfs_mknod() POV we just have a negative dentry -
  	 * all is fine. Let's be bastards - you had / on the end, you've
  	 * been asking for (non-existent) directory. -ENOENT for you.
  	 */
  	if (unlikely(!is_dir && last.name[last.len])) {
  		error = -ENOENT;
  		goto fail;
  	}
  	if (unlikely(err2)) {
  		error = err2;
  		goto fail;
  	}
  	putname(name);
  	return dentry;
  fail:
  	dput(dentry);
  	dentry = ERR_PTR(error);
  unlock:
  	mutex_unlock(&path->dentry->d_inode->i_mutex);
  	if (!err2)
  		mnt_drop_write(path->mnt);
  out:
  	path_put(path);
  	putname(name);
  	return dentry;
  }
  
  struct dentry *kern_path_create(int dfd, const char *pathname,
  				struct path *path, unsigned int lookup_flags)
  {
  	return filename_create(dfd, getname_kernel(pathname),
  				path, lookup_flags);
  }
  EXPORT_SYMBOL(kern_path_create);
  
  void done_path_create(struct path *path, struct dentry *dentry)
  {
  	dput(dentry);
  	mutex_unlock(&path->dentry->d_inode->i_mutex);
  	mnt_drop_write(path->mnt);
  	path_put(path);
  }
  EXPORT_SYMBOL(done_path_create);
  
  inline struct dentry *user_path_create(int dfd, const char __user *pathname,
  				struct path *path, unsigned int lookup_flags)
  {
  	return filename_create(dfd, getname(pathname), path, lookup_flags);
  }
  EXPORT_SYMBOL(user_path_create);
  
  int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
  {
  	int error = may_create(dir, dentry);
  
  	if (error)
  		return error;
  
  	if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD))
  		return -EPERM;
  
  	if (!dir->i_op->mknod)
  		return -EPERM;
  
  	error = devcgroup_inode_mknod(mode, dev);
  	if (error)
  		return error;
  
  	error = security_inode_mknod(dir, dentry, mode, dev);
  	if (error)
  		return error;
  
  	error = dir->i_op->mknod(dir, dentry, mode, dev);
  	if (!error)
  		fsnotify_create(dir, dentry);
  	return error;
  }
  EXPORT_SYMBOL(vfs_mknod);
  
  static int may_mknod(umode_t mode)
  {
  	switch (mode & S_IFMT) {
  	case S_IFREG:
  	case S_IFCHR:
  	case S_IFBLK:
  	case S_IFIFO:
  	case S_IFSOCK:
  	case 0: /* zero mode translates to S_IFREG */
  		return 0;
  	case S_IFDIR:
  		return -EPERM;
  	default:
  		return -EINVAL;
  	}
  }
  
  SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
  		unsigned, dev)
  {
  	struct dentry *dentry;
  	struct path path;
  	int error;
  	unsigned int lookup_flags = 0;
  
  	error = may_mknod(mode);
  	if (error)
  		return error;
  retry:
  	dentry = user_path_create(dfd, filename, &path, lookup_flags);
  	if (IS_ERR(dentry))
  		return PTR_ERR(dentry);
  
  	if (!IS_POSIXACL(path.dentry->d_inode))
  		mode &= ~current_umask();
  	error = security_path_mknod(&path, dentry, mode, dev);
  	if (error)
  		goto out;
  	switch (mode & S_IFMT) {
  		case 0: case S_IFREG:
  			error = vfs_create(path.dentry->d_inode,dentry,mode,true);
  			break;
  		case S_IFCHR: case S_IFBLK:
  			error = vfs_mknod(path.dentry->d_inode,dentry,mode,
  					new_decode_dev(dev));
  			break;
  		case S_IFIFO: case S_IFSOCK:
  			error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
  			break;
  	}
  out:
  	done_path_create(&path, dentry);
  	if (retry_estale(error, lookup_flags)) {
  		lookup_flags |= LOOKUP_REVAL;
  		goto retry;
  	}
  	return error;
  }
  
  SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, dev)
  {
  	return sys_mknodat(AT_FDCWD, filename, mode, dev);
  }
  
  int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
  {
  	int error = may_create(dir, dentry);
  	unsigned max_links = dir->i_sb->s_max_links;
  
  	if (error)
  		return error;
  
  	if (!dir->i_op->mkdir)
  		return -EPERM;
  
  	mode &= (S_IRWXUGO|S_ISVTX);
  	error = security_inode_mkdir(dir, dentry, mode);
  	if (error)
  		return error;
  
  	if (max_links && dir->i_nlink >= max_links)
  		return -EMLINK;
  
  	error = dir->i_op->mkdir(dir, dentry, mode);
  	if (!error)
  		fsnotify_mkdir(dir, dentry);
  	return error;
  }
  EXPORT_SYMBOL(vfs_mkdir);
  
  SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
  {
  	struct dentry *dentry;
  	struct path path;
  	int error;
  	unsigned int lookup_flags = LOOKUP_DIRECTORY;
  
  retry:
  	dentry = user_path_create(dfd, pathname, &path, lookup_flags);
  	if (IS_ERR(dentry))
  		return PTR_ERR(dentry);
  
  	if (!IS_POSIXACL(path.dentry->d_inode))
  		mode &= ~current_umask();
  	error = security_path_mkdir(&path, dentry, mode);
  	if (!error)
  		error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
  	done_path_create(&path, dentry);
  	if (retry_estale(error, lookup_flags)) {
  		lookup_flags |= LOOKUP_REVAL;
  		goto retry;
  	}
  	return error;
  }
  
  SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode)
  {
  	return sys_mkdirat(AT_FDCWD, pathname, mode);
  }
  
  /*
   * The dentry_unhash() helper will try to drop the dentry early: we
   * should have a usage count of 1 if we're the only user of this
   * dentry, and if that is true (possibly after pruning the dcache),
   * then we drop the dentry now.
   *
   * A low-level filesystem can, if it choses, legally
   * do a
   *
   *	if (!d_unhashed(dentry))
   *		return -EBUSY;
   *
   * if it cannot handle the case of removing a directory
   * that is still in use by something else..
   */
  void dentry_unhash(struct dentry *dentry)
  {
  	shrink_dcache_parent(dentry);
  	spin_lock(&dentry->d_lock);
  	if (dentry->d_lockref.count == 1)
  		__d_drop(dentry);
  	spin_unlock(&dentry->d_lock);
  }
  EXPORT_SYMBOL(dentry_unhash);
  
  int vfs_rmdir(struct inode *dir, struct dentry *dentry)
  {
  	int error = may_delete(dir, dentry, 1);
  
  	if (error)
  		return error;
  
  	if (!dir->i_op->rmdir)
  		return -EPERM;
  
  	dget(dentry);
  	mutex_lock(&dentry->d_inode->i_mutex);
  
  	error = -EBUSY;
  	if (is_local_mountpoint(dentry))
  		goto out;
  
  	error = security_inode_rmdir(dir, dentry);
  	if (error)
  		goto out;
  
  	shrink_dcache_parent(dentry);
  	error = dir->i_op->rmdir(dir, dentry);
  	if (error)
  		goto out;
  
  	dentry->d_inode->i_flags |= S_DEAD;
  	dont_mount(dentry);
  	detach_mounts(dentry);
  
  out:
  	mutex_unlock(&dentry->d_inode->i_mutex);
  	dput(dentry);
  	if (!error)
  		d_delete(dentry);
  	return error;
  }
  EXPORT_SYMBOL(vfs_rmdir);
  
  static long do_rmdir(int dfd, const char __user *pathname)
  {
  	int error = 0;
  	struct filename *name;
  	struct dentry *dentry;
  	struct path path;
  	struct qstr last;
  	int type;
  	unsigned int lookup_flags = 0;
  retry:
  	name = user_path_parent(dfd, pathname,
  				&path, &last, &type, lookup_flags);
  	if (IS_ERR(name))
  		return PTR_ERR(name);
  
  	switch (type) {
  	case LAST_DOTDOT:
  		error = -ENOTEMPTY;
  		goto exit1;
  	case LAST_DOT:
  		error = -EINVAL;
  		goto exit1;
  	case LAST_ROOT:
  		error = -EBUSY;
  		goto exit1;
  	}
  
  	error = mnt_want_write(path.mnt);
  	if (error)
  		goto exit1;
  
  	mutex_lock_nested(&path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
  	dentry = __lookup_hash(&last, path.dentry, lookup_flags);
  	error = PTR_ERR(dentry);
  	if (IS_ERR(dentry))
  		goto exit2;
  	if (!dentry->d_inode) {
  		error = -ENOENT;
  		goto exit3;
  	}
  	error = security_path_rmdir(&path, dentry);
  	if (error)
  		goto exit3;
  	error = vfs_rmdir(path.dentry->d_inode, dentry);
  exit3:
  	dput(dentry);
  exit2:
  	mutex_unlock(&path.dentry->d_inode->i_mutex);
  	mnt_drop_write(path.mnt);
  exit1:
  	path_put(&path);
  	putname(name);
  	if (retry_estale(error, lookup_flags)) {
  		lookup_flags |= LOOKUP_REVAL;
  		goto retry;
  	}
  	return error;
  }
  
  SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
  {
  	return do_rmdir(AT_FDCWD, pathname);
  }
  
  /**
   * vfs_unlink - unlink a filesystem object
   * @dir:	parent directory
   * @dentry:	victim
   * @delegated_inode: returns victim inode, if the inode is delegated.
   *
   * The caller must hold dir->i_mutex.
   *
   * If vfs_unlink discovers a delegation, it will return -EWOULDBLOCK and
   * return a reference to the inode in delegated_inode.  The caller
   * should then break the delegation on that inode and retry.  Because
   * breaking a delegation may take a long time, the caller should drop
   * dir->i_mutex before doing so.
   *
   * Alternatively, a caller may pass NULL for delegated_inode.  This may
   * be appropriate for callers that expect the underlying filesystem not
   * to be NFS exported.
   */
  int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegated_inode)
  {
  	struct inode *target = dentry->d_inode;
  	int error = may_delete(dir, dentry, 0);
  
  	if (error)
  		return error;
  
  	if (!dir->i_op->unlink)
  		return -EPERM;
  
  	mutex_lock(&target->i_mutex);
  	if (is_local_mountpoint(dentry))
  		error = -EBUSY;
  	else {
  		error = security_inode_unlink(dir, dentry);
  		if (!error) {
  			error = try_break_deleg(target, delegated_inode);
  			if (error)
  				goto out;
  			error = dir->i_op->unlink(dir, dentry);
  			if (!error) {
  				dont_mount(dentry);
  				detach_mounts(dentry);
  			}
  		}
  	}
  out:
  	mutex_unlock(&target->i_mutex);
  
  	/* We don't d_delete() NFS sillyrenamed files--they still exist. */
  	if (!error && !(dentry->d_flags & DCACHE_NFSFS_RENAMED)) {
  		fsnotify_link_count(target);
  		d_delete(dentry);
  	}
  
  	return error;
  }
  EXPORT_SYMBOL(vfs_unlink);
  
  /*
   * Make sure that the actual truncation of the file will occur outside its
   * directory's i_mutex.  Truncate can take a long time if there is a lot of
   * writeout happening, and we don't want to prevent access to the directory
   * while waiting on the I/O.
   */
  static long do_unlinkat(int dfd, const char __user *pathname)
  {
  	int error;
  	struct filename *name;
  	struct dentry *dentry;
  	struct path path;
  	struct qstr last;
  	int type;
  	struct inode *inode = NULL;
  	struct inode *delegated_inode = NULL;
  	unsigned int lookup_flags = 0;
  retry:
  	name = user_path_parent(dfd, pathname,
  				&path, &last, &type, lookup_flags);
  	if (IS_ERR(name))
  		return PTR_ERR(name);
  
  	error = -EISDIR;
  	if (type != LAST_NORM)
  		goto exit1;
  
  	error = mnt_want_write(path.mnt);
  	if (error)
  		goto exit1;
  retry_deleg:
  	mutex_lock_nested(&path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
  	dentry = __lookup_hash(&last, path.dentry, lookup_flags);
  	error = PTR_ERR(dentry);
  	if (!IS_ERR(dentry)) {
  		/* Why not before? Because we want correct error value */
  		if (last.name[last.len])
  			goto slashes;
  		inode = dentry->d_inode;
  		if (d_is_negative(dentry))
  			goto slashes;
  		ihold(inode);
  		error = security_path_unlink(&path, dentry);
  		if (error)
  			goto exit2;
  		error = vfs_unlink(path.dentry->d_inode, dentry, &delegated_inode);
  exit2:
  		dput(dentry);
  	}
  	mutex_unlock(&path.dentry->d_inode->i_mutex);
  	if (inode)
  		iput(inode);	/* truncate the inode here */
  	inode = NULL;
  	if (delegated_inode) {
  		error = break_deleg_wait(&delegated_inode);
  		if (!error)
  			goto retry_deleg;
  	}
  	mnt_drop_write(path.mnt);
  exit1:
  	path_put(&path);
  	putname(name);
  	if (retry_estale(error, lookup_flags)) {
  		lookup_flags |= LOOKUP_REVAL;
  		inode = NULL;
  		goto retry;
  	}
  	return error;
  
  slashes:
  	if (d_is_negative(dentry))
  		error = -ENOENT;
  	else if (d_is_dir(dentry))
  		error = -EISDIR;
  	else
  		error = -ENOTDIR;
  	goto exit2;
  }
  
  SYSCALL_DEFINE3(unlinkat, int, dfd, const char __user *, pathname, int, flag)
  {
  	if ((flag & ~AT_REMOVEDIR) != 0)
  		return -EINVAL;
  
  	if (flag & AT_REMOVEDIR)
  		return do_rmdir(dfd, pathname);
  
  	return do_unlinkat(dfd, pathname);
  }
  
  SYSCALL_DEFINE1(unlink, const char __user *, pathname)
  {
  	return do_unlinkat(AT_FDCWD, pathname);
  }
  
  int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname)
  {
  	int error = may_create(dir, dentry);
  
  	if (error)
  		return error;
  
  	if (!dir->i_op->symlink)
  		return -EPERM;
  
  	error = security_inode_symlink(dir, dentry, oldname);
  	if (error)
  		return error;
  
  	error = dir->i_op->symlink(dir, dentry, oldname);
  	if (!error)
  		fsnotify_create(dir, dentry);
  	return error;
  }
  EXPORT_SYMBOL(vfs_symlink);
  
  SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
  		int, newdfd, const char __user *, newname)
  {
  	int error;
  	struct filename *from;
  	struct dentry *dentry;
  	struct path path;
  	unsigned int lookup_flags = 0;
  
  	from = getname(oldname);
  	if (IS_ERR(from))
  		return PTR_ERR(from);
  retry:
  	dentry = user_path_create(newdfd, newname, &path, lookup_flags);
  	error = PTR_ERR(dentry);
  	if (IS_ERR(dentry))
  		goto out_putname;
  
  	error = security_path_symlink(&path, dentry, from->name);
  	if (!error)
  		error = vfs_symlink(path.dentry->d_inode, dentry, from->name);
  	done_path_create(&path, dentry);
  	if (retry_estale(error, lookup_flags)) {
  		lookup_flags |= LOOKUP_REVAL;
  		goto retry;
  	}
  out_putname:
  	putname(from);
  	return error;
  }
  
  SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newname)
  {
  	return sys_symlinkat(oldname, AT_FDCWD, newname);
  }
  
  /**
   * vfs_link - create a new link
   * @old_dentry:	object to be linked
   * @dir:	new parent
   * @new_dentry:	where to create the new link
   * @delegated_inode: returns inode needing a delegation break
   *
   * The caller must hold dir->i_mutex
   *
   * If vfs_link discovers a delegation on the to-be-linked file in need
   * of breaking, it will return -EWOULDBLOCK and return a reference to the
   * inode in delegated_inode.  The caller should then break the delegation
   * and retry.  Because breaking a delegation may take a long time, the
   * caller should drop the i_mutex before doing so.
   *
   * Alternatively, a caller may pass NULL for delegated_inode.  This may
   * be appropriate for callers that expect the underlying filesystem not
   * to be NFS exported.
   */
  int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry, struct inode **delegated_inode)
  {
  	struct inode *inode = old_dentry->d_inode;
  	unsigned max_links = dir->i_sb->s_max_links;
  	int error;
  
  	if (!inode)
  		return -ENOENT;
  
  	error = may_create(dir, new_dentry);
  	if (error)
  		return error;
  
  	if (dir->i_sb != inode->i_sb)
  		return -EXDEV;
  
  	/*
  	 * A link to an append-only or immutable file cannot be created.
  	 */
  	if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
  		return -EPERM;
  	if (!dir->i_op->link)
  		return -EPERM;
  	if (S_ISDIR(inode->i_mode))
  		return -EPERM;
  
  	error = security_inode_link(old_dentry, dir, new_dentry);
  	if (error)
  		return error;
  
  	mutex_lock(&inode->i_mutex);
  	/* Make sure we don't allow creating hardlink to an unlinked file */
  	if (inode->i_nlink == 0 && !(inode->i_state & I_LINKABLE))
  		error =  -ENOENT;
  	else if (max_links && inode->i_nlink >= max_links)
  		error = -EMLINK;
  	else {
  		error = try_break_deleg(inode, delegated_inode);
  		if (!error)
  			error = dir->i_op->link(old_dentry, dir, new_dentry);
  	}
  
  	if (!error && (inode->i_state & I_LINKABLE)) {
  		spin_lock(&inode->i_lock);
  		inode->i_state &= ~I_LINKABLE;
  		spin_unlock(&inode->i_lock);
  	}
  	mutex_unlock(&inode->i_mutex);
  	if (!error)
  		fsnotify_link(dir, inode, new_dentry);
  	return error;
  }
  EXPORT_SYMBOL(vfs_link);
  
  /*
   * Hardlinks are often used in delicate situations.  We avoid
   * security-related surprises by not following symlinks on the
   * newname.  --KAB
   *
   * We don't follow them on the oldname either to be compatible
   * with linux 2.0, and to avoid hard-linking to directories
   * and other special files.  --ADM
   */
  SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
  		int, newdfd, const char __user *, newname, int, flags)
  {
  	struct dentry *new_dentry;
  	struct path old_path, new_path;
  	struct inode *delegated_inode = NULL;
  	int how = 0;
  	int error;
  
  	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
  		return -EINVAL;
  	/*
  	 * To use null names we require CAP_DAC_READ_SEARCH
  	 * This ensures that not everyone will be able to create
  	 * handlink using the passed filedescriptor.
  	 */
  	if (flags & AT_EMPTY_PATH) {
  		if (!capable(CAP_DAC_READ_SEARCH))
  			return -ENOENT;
  		how = LOOKUP_EMPTY;
  	}
  
  	if (flags & AT_SYMLINK_FOLLOW)
  		how |= LOOKUP_FOLLOW;
  retry:
  	error = user_path_at(olddfd, oldname, how, &old_path);
  	if (error)
  		return error;
  
  	new_dentry = user_path_create(newdfd, newname, &new_path,
  					(how & LOOKUP_REVAL));
  	error = PTR_ERR(new_dentry);
  	if (IS_ERR(new_dentry))
  		goto out;
  
  	error = -EXDEV;
  	if (old_path.mnt != new_path.mnt)
  		goto out_dput;
  	error = may_linkat(&old_path);
  	if (unlikely(error))
  		goto out_dput;
  	error = security_path_link(old_path.dentry, &new_path, new_dentry);
  	if (error)
  		goto out_dput;
  	error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry, &delegated_inode);
  out_dput:
  	done_path_create(&new_path, new_dentry);
  	if (delegated_inode) {
  		error = break_deleg_wait(&delegated_inode);
  		if (!error) {
  			path_put(&old_path);
  			goto retry;
  		}
  	}
  	if (retry_estale(error, how)) {
  		path_put(&old_path);
  		how |= LOOKUP_REVAL;
  		goto retry;
  	}
  out:
  	path_put(&old_path);
  
  	return error;
  }
  
  SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname)
  {
  	return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
  }
  
  /**
   * vfs_rename - rename a filesystem object
   * @old_dir:	parent of source
   * @old_dentry:	source
   * @new_dir:	parent of destination
   * @new_dentry:	destination
   * @delegated_inode: returns an inode needing a delegation break
   * @flags:	rename flags
   *
   * The caller must hold multiple mutexes--see lock_rename()).
   *
   * If vfs_rename discovers a delegation in need of breaking at either
   * the source or destination, it will return -EWOULDBLOCK and return a
   * reference to the inode in delegated_inode.  The caller should then
   * break the delegation and retry.  Because breaking a delegation may
   * take a long time, the caller should drop all locks before doing
   * so.
   *
   * Alternatively, a caller may pass NULL for delegated_inode.  This may
   * be appropriate for callers that expect the underlying filesystem not
   * to be NFS exported.
   *
   * The worst of all namespace operations - renaming directory. "Perverted"
   * doesn't even start to describe it. Somebody in UCB had a heck of a trip...
   * Problems:
   *	a) we can get into loop creation.
   *	b) race potential - two innocent renames can create a loop together.
   *	   That's where 4.4 screws up. Current fix: serialization on
   *	   sb->s_vfs_rename_mutex. We might be more accurate, but that's another
   *	   story.
   *	c) we have to lock _four_ objects - parents and victim (if it exists),
   *	   and source (if it is not a directory).
   *	   And that - after we got ->i_mutex on parents (until then we don't know
   *	   whether the target exists).  Solution: try to be smart with locking
   *	   order for inodes.  We rely on the fact that tree topology may change
   *	   only under ->s_vfs_rename_mutex _and_ that parent of the object we
   *	   move will be locked.  Thus we can rank directories by the tree
   *	   (ancestors first) and rank all non-directories after them.
   *	   That works since everybody except rename does "lock parent, lookup,
   *	   lock child" and rename is under ->s_vfs_rename_mutex.
   *	   HOWEVER, it relies on the assumption that any object with ->lookup()
   *	   has no more than 1 dentry.  If "hybrid" objects will ever appear,
   *	   we'd better make sure that there's no link(2) for them.
   *	d) conversion from fhandle to dentry may come in the wrong moment - when
   *	   we are removing the target. Solution: we will have to grab ->i_mutex
   *	   in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on
   *	   ->i_mutex on parents, which works but leads to some truly excessive
   *	   locking].
   */
  int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
  	       struct inode *new_dir, struct dentry *new_dentry,
  	       struct inode **delegated_inode, unsigned int flags)
  {
  	int error;
  	bool is_dir = d_is_dir(old_dentry);
  	const unsigned char *old_name;
  	struct inode *source = old_dentry->d_inode;
  	struct inode *target = new_dentry->d_inode;
  	bool new_is_dir = false;
  	unsigned max_links = new_dir->i_sb->s_max_links;
  
  	if (source == target)
  		return 0;
  
  	error = may_delete(old_dir, old_dentry, is_dir);
  	if (error)
  		return error;
  
  	if (!target) {
  		error = may_create(new_dir, new_dentry);
  	} else {
  		new_is_dir = d_is_dir(new_dentry);
  
  		if (!(flags & RENAME_EXCHANGE))
  			error = may_delete(new_dir, new_dentry, is_dir);
  		else
  			error = may_delete(new_dir, new_dentry, new_is_dir);
  	}
  	if (error)
  		return error;
  
  	if (!old_dir->i_op->rename && !old_dir->i_op->rename2)
  		return -EPERM;
  
  	if (flags && !old_dir->i_op->rename2)
  		return -EINVAL;
  
  	/*
  	 * If we are going to change the parent - check write permissions,
  	 * we'll need to flip '..'.
  	 */
  	if (new_dir != old_dir) {
  		if (is_dir) {
  			error = inode_permission(source, MAY_WRITE);
  			if (error)
  				return error;
  		}
  		if ((flags & RENAME_EXCHANGE) && new_is_dir) {
  			error = inode_permission(target, MAY_WRITE);
  			if (error)
  				return error;
  		}
  	}
  
  	error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry,
  				      flags);
  	if (error)
  		return error;
  
  	old_name = fsnotify_oldname_init(old_dentry->d_name.name);
  	dget(new_dentry);
  	if (!is_dir || (flags & RENAME_EXCHANGE))
  		lock_two_nondirectories(source, target);
  	else if (target)
  		mutex_lock(&target->i_mutex);
  
  	error = -EBUSY;
  	if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry))
  		goto out;
  
  	if (max_links && new_dir != old_dir) {
  		error = -EMLINK;
  		if (is_dir && !new_is_dir && new_dir->i_nlink >= max_links)
  			goto out;
  		if ((flags & RENAME_EXCHANGE) && !is_dir && new_is_dir &&
  		    old_dir->i_nlink >= max_links)
  			goto out;
  	}
  	if (is_dir && !(flags & RENAME_EXCHANGE) && target)
  		shrink_dcache_parent(new_dentry);
  	if (!is_dir) {
  		error = try_break_deleg(source, delegated_inode);
  		if (error)
  			goto out;
  	}
  	if (target && !new_is_dir) {
  		error = try_break_deleg(target, delegated_inode);
  		if (error)
  			goto out;
  	}
  	if (!old_dir->i_op->rename2) {
  		error = old_dir->i_op->rename(old_dir, old_dentry,
  					      new_dir, new_dentry);
  	} else {
  		WARN_ON(old_dir->i_op->rename != NULL);
  		error = old_dir->i_op->rename2(old_dir, old_dentry,
  					       new_dir, new_dentry, flags);
  	}
  	if (error)
  		goto out;
  
  	if (!(flags & RENAME_EXCHANGE) && target) {
  		if (is_dir)
  			target->i_flags |= S_DEAD;
  		dont_mount(new_dentry);
  		detach_mounts(new_dentry);
  	}
  	if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) {
  		if (!(flags & RENAME_EXCHANGE))
  			d_move(old_dentry, new_dentry);
  		else
  			d_exchange(old_dentry, new_dentry);
  	}
  out:
  	if (!is_dir || (flags & RENAME_EXCHANGE))
  		unlock_two_nondirectories(source, target);
  	else if (target)
  		mutex_unlock(&target->i_mutex);
  	dput(new_dentry);
  	if (!error) {
  		fsnotify_move(old_dir, new_dir, old_name, is_dir,
  			      !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
  		if (flags & RENAME_EXCHANGE) {
  			fsnotify_move(new_dir, old_dir, old_dentry->d_name.name,
  				      new_is_dir, NULL, new_dentry);
  		}
  	}
  	fsnotify_oldname_free(old_name);
  
  	return error;
  }
  EXPORT_SYMBOL(vfs_rename);
  
  SYSCALL_DEFINE5(renameat2, int, olddfd, const char __user *, oldname,
  		int, newdfd, const char __user *, newname, unsigned int, flags)
  {
  	struct dentry *old_dentry, *new_dentry;
  	struct dentry *trap;
  	struct path old_path, new_path;
  	struct qstr old_last, new_last;
  	int old_type, new_type;
  	struct inode *delegated_inode = NULL;
  	struct filename *from;
  	struct filename *to;
  	unsigned int lookup_flags = 0, target_flags = LOOKUP_RENAME_TARGET;
  	bool should_retry = false;
  	int error;
  
  	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
  		return -EINVAL;
  
  	if ((flags & (RENAME_NOREPLACE | RENAME_WHITEOUT)) &&
  	    (flags & RENAME_EXCHANGE))
  		return -EINVAL;
  
  	if ((flags & RENAME_WHITEOUT) && !capable(CAP_MKNOD))
  		return -EPERM;
  
  	if (flags & RENAME_EXCHANGE)
  		target_flags = 0;
  
  retry:
  	from = user_path_parent(olddfd, oldname,
  				&old_path, &old_last, &old_type, lookup_flags);
  	if (IS_ERR(from)) {
  		error = PTR_ERR(from);
  		goto exit;
  	}
  
  	to = user_path_parent(newdfd, newname,
  				&new_path, &new_last, &new_type, lookup_flags);
  	if (IS_ERR(to)) {
  		error = PTR_ERR(to);
  		goto exit1;
  	}
  
  	error = -EXDEV;
  	if (old_path.mnt != new_path.mnt)
  		goto exit2;
  
  	error = -EBUSY;
  	if (old_type != LAST_NORM)
  		goto exit2;
  
  	if (flags & RENAME_NOREPLACE)
  		error = -EEXIST;
  	if (new_type != LAST_NORM)
  		goto exit2;
  
  	error = mnt_want_write(old_path.mnt);
  	if (error)
  		goto exit2;
  
  retry_deleg:
  	trap = lock_rename(new_path.dentry, old_path.dentry);
  
  	old_dentry = __lookup_hash(&old_last, old_path.dentry, lookup_flags);
  	error = PTR_ERR(old_dentry);
  	if (IS_ERR(old_dentry))
  		goto exit3;
  	/* source must exist */
  	error = -ENOENT;
  	if (d_is_negative(old_dentry))
  		goto exit4;
  	new_dentry = __lookup_hash(&new_last, new_path.dentry, lookup_flags | target_flags);
  	error = PTR_ERR(new_dentry);
  	if (IS_ERR(new_dentry))
  		goto exit4;
  	error = -EEXIST;
  	if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry))
  		goto exit5;
  	if (flags & RENAME_EXCHANGE) {
  		error = -ENOENT;
  		if (d_is_negative(new_dentry))
  			goto exit5;
  
  		if (!d_is_dir(new_dentry)) {
  			error = -ENOTDIR;
  			if (new_last.name[new_last.len])
  				goto exit5;
  		}
  	}
  	/* unless the source is a directory trailing slashes give -ENOTDIR */
  	if (!d_is_dir(old_dentry)) {
  		error = -ENOTDIR;
  		if (old_last.name[old_last.len])
  			goto exit5;
  		if (!(flags & RENAME_EXCHANGE) && new_last.name[new_last.len])
  			goto exit5;
  	}
  	/* source should not be ancestor of target */
  	error = -EINVAL;
  	if (old_dentry == trap)
  		goto exit5;
  	/* target should not be an ancestor of source */
  	if (!(flags & RENAME_EXCHANGE))
  		error = -ENOTEMPTY;
  	if (new_dentry == trap)
  		goto exit5;
  
  	error = security_path_rename(&old_path, old_dentry,
  				     &new_path, new_dentry, flags);
  	if (error)
  		goto exit5;
  	error = vfs_rename(old_path.dentry->d_inode, old_dentry,
  			   new_path.dentry->d_inode, new_dentry,
  			   &delegated_inode, flags);
  exit5:
  	dput(new_dentry);
  exit4:
  	dput(old_dentry);
  exit3:
  	unlock_rename(new_path.dentry, old_path.dentry);
  	if (delegated_inode) {
  		error = break_deleg_wait(&delegated_inode);
  		if (!error)
  			goto retry_deleg;
  	}
  	mnt_drop_write(old_path.mnt);
  exit2:
  	if (retry_estale(error, lookup_flags))
  		should_retry = true;
  	path_put(&new_path);
  	putname(to);
  exit1:
  	path_put(&old_path);
  	putname(from);
  	if (should_retry) {
  		should_retry = false;
  		lookup_flags |= LOOKUP_REVAL;
  		goto retry;
  	}
  exit:
  	return error;
  }
  
  SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
  		int, newdfd, const char __user *, newname)
  {
  	return sys_renameat2(olddfd, oldname, newdfd, newname, 0);
  }
  
  SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newname)
  {
  	return sys_renameat2(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
  }
  
  int vfs_whiteout(struct inode *dir, struct dentry *dentry)
  {
  	int error = may_create(dir, dentry);
  	if (error)
  		return error;
  
  	if (!dir->i_op->mknod)
  		return -EPERM;
  
  	return dir->i_op->mknod(dir, dentry,
  				S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV);
  }
  EXPORT_SYMBOL(vfs_whiteout);
  
  int readlink_copy(char __user *buffer, int buflen, const char *link)
  {
  	int len = PTR_ERR(link);
  	if (IS_ERR(link))
  		goto out;
  
  	len = strlen(link);
  	if (len > (unsigned) buflen)
  		len = buflen;
  	if (copy_to_user(buffer, link, len))
  		len = -EFAULT;
  out:
  	return len;
  }
  EXPORT_SYMBOL(readlink_copy);
  
  /*
   * A helper for ->readlink().  This should be used *ONLY* for symlinks that
   * have ->follow_link() touching nd only in nd_set_link().  Using (or not
   * using) it for any given inode is up to filesystem.
   */
  int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen)
  {
  	void *cookie;
  	struct inode *inode = d_inode(dentry);
  	const char *link = inode->i_link;
  	int res;
  
  	if (!link) {
  		link = inode->i_op->follow_link(dentry, &cookie);
  		if (IS_ERR(link))
  			return PTR_ERR(link);
  	}
  	res = readlink_copy(buffer, buflen, link);
  	if (inode->i_op->put_link)
  		inode->i_op->put_link(inode, cookie);
  	return res;
  }
  EXPORT_SYMBOL(generic_readlink);
  
  /* get the link contents into pagecache */
  static char *page_getlink(struct dentry * dentry, struct page **ppage)
  {
  	char *kaddr;
  	struct page *page;
  	struct address_space *mapping = dentry->d_inode->i_mapping;
  	page = read_mapping_page(mapping, 0, NULL);
  	if (IS_ERR(page))
  		return (char*)page;
  	*ppage = page;
  	kaddr = kmap(page);
  	nd_terminate_link(kaddr, dentry->d_inode->i_size, PAGE_SIZE - 1);
  	return kaddr;
  }
  
  int page_readlink(struct dentry *dentry, char __user *buffer, int buflen)
  {
  	struct page *page = NULL;
  	int res = readlink_copy(buffer, buflen, page_getlink(dentry, &page));
  	if (page) {
  		kunmap(page);
  		page_cache_release(page);
  	}
  	return res;
  }
  EXPORT_SYMBOL(page_readlink);
  
  const char *page_follow_link_light(struct dentry *dentry, void **cookie)
  {
  	struct page *page = NULL;
  	char *res = page_getlink(dentry, &page);
  	if (!IS_ERR(res))
  		*cookie = page;
  	return res;
  }
  EXPORT_SYMBOL(page_follow_link_light);
  
  void page_put_link(struct inode *unused, void *cookie)
  {
  	struct page *page = cookie;
  	kunmap(page);
  	page_cache_release(page);
  }
  EXPORT_SYMBOL(page_put_link);
  
  /*
   * The nofs argument instructs pagecache_write_begin to pass AOP_FLAG_NOFS
   */
  int __page_symlink(struct inode *inode, const char *symname, int len, int nofs)
  {
  	struct address_space *mapping = inode->i_mapping;
  	struct page *page;
  	void *fsdata;
  	int err;
  	char *kaddr;
  	unsigned int flags = AOP_FLAG_UNINTERRUPTIBLE;
  	if (nofs)
  		flags |= AOP_FLAG_NOFS;
  
  retry:
  	err = pagecache_write_begin(NULL, mapping, 0, len-1,
  				flags, &page, &fsdata);
  	if (err)
  		goto fail;
  
  	kaddr = kmap_atomic(page);
  	memcpy(kaddr, symname, len-1);
  	kunmap_atomic(kaddr);
  
  	err = pagecache_write_end(NULL, mapping, 0, len-1, len-1,
  							page, fsdata);
  	if (err < 0)
  		goto fail;
  	if (err < len-1)
  		goto retry;
  
  	mark_inode_dirty(inode);
  	return 0;
  fail:
  	return err;
  }
  EXPORT_SYMBOL(__page_symlink);
  
  int page_symlink(struct inode *inode, const char *symname, int len)
  {
  	return __page_symlink(inode, symname, len,
  			!(mapping_gfp_mask(inode->i_mapping) & __GFP_FS));
  }
  EXPORT_SYMBOL(page_symlink);
  
  const struct inode_operations page_symlink_inode_operations = {
  	.readlink	= generic_readlink,
  	.follow_link	= page_follow_link_light,
  	.put_link	= page_put_link,
  };
  EXPORT_SYMBOL(page_symlink_inode_operations);
  