text: /*
   * linux/fs/reiserfs/xattr.c
   *
   * Copyright (c) 2002 by Jeff Mahoney, <jeffm@suse.com>
   *
   */
  
  /*
   * In order to implement EA/ACLs in a clean, backwards compatible manner,
   * they are implemented as files in a "private" directory.
   * Each EA is in it's own file, with the directory layout like so (/ is assumed
   * to be relative to fs root). Inside the /.reiserfs_priv/xattrs directory,
   * directories named using the capital-hex form of the objectid and
   * generation number are used. Inside each directory are individual files
   * named with the name of the extended attribute.
   *
   * So, for objectid 12648430, we could have:
   * /.reiserfs_priv/xattrs/C0FFEE.0/system.posix_acl_access
   * /.reiserfs_priv/xattrs/C0FFEE.0/system.posix_acl_default
   * /.reiserfs_priv/xattrs/C0FFEE.0/user.Content-Type
   * .. or similar.
   *
   * The file contents are the text of the EA. The size is known based on the
   * stat data describing the file.
   *
   * In the case of system.posix_acl_access and system.posix_acl_default, since
   * these are special cases for filesystem ACLs, they are interpreted by the
   * kernel, in addition, they are negatively and positively cached and attached
   * to the inode so that unnecessary lookups are avoided.
   *
   * Locking works like so:
   * Directory components (xattr root, xattr dir) are protectd by their i_mutex.
   * The xattrs themselves are protected by the xattr_sem.
   */
  
  #include "reiserfs.h"
  #include <linux/capability.h>
  #include <linux/dcache.h>
  #include <linux/namei.h>
  #include <linux/errno.h>
  #include <linux/gfp.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/pagemap.h>
  #include <linux/xattr.h>
  #include "xattr.h"
  #include "acl.h"
  #include <linux/uaccess.h>
  #include <net/checksum.h>
  #include <linux/stat.h>
  #include <linux/quotaops.h>
  #include <linux/security.h>
  #include <linux/posix_acl_xattr.h>
  
  #define PRIVROOT_NAME ".reiserfs_priv"
  #define XAROOT_NAME   "xattrs"
  
  
  /*
   * Helpers for inode ops. We do this so that we don't have all the VFS
   * overhead and also for proper i_mutex annotation.
   * dir->i_mutex must be held for all of them.
   */
  #ifdef CONFIG_REISERFS_FS_XATTR
  static int xattr_create(struct inode *dir, struct dentry *dentry, int mode)
  {
  	BUG_ON(!mutex_is_locked(&dir->i_mutex));
  	return dir->i_op->create(dir, dentry, mode, true);
  }
  #endif
  
  static int xattr_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
  {
  	BUG_ON(!mutex_is_locked(&dir->i_mutex));
  	return dir->i_op->mkdir(dir, dentry, mode);
  }
  
  /*
   * We use I_MUTEX_CHILD here to silence lockdep. It's safe because xattr
   * mutation ops aren't called during rename or splace, which are the
   * only other users of I_MUTEX_CHILD. It violates the ordering, but that's
   * better than allocating another subclass just for this code.
   */
  static int xattr_unlink(struct inode *dir, struct dentry *dentry)
  {
  	int error;
  
  	BUG_ON(!mutex_is_locked(&dir->i_mutex));
  
  	mutex_lock_nested(&d_inode(dentry)->i_mutex, I_MUTEX_CHILD);
  	error = dir->i_op->unlink(dir, dentry);
  	mutex_unlock(&d_inode(dentry)->i_mutex);
  
  	if (!error)
  		d_delete(dentry);
  	return error;
  }
  
  static int xattr_rmdir(struct inode *dir, struct dentry *dentry)
  {
  	int error;
  
  	BUG_ON(!mutex_is_locked(&dir->i_mutex));
  
  	mutex_lock_nested(&d_inode(dentry)->i_mutex, I_MUTEX_CHILD);
  	error = dir->i_op->rmdir(dir, dentry);
  	if (!error)
  		d_inode(dentry)->i_flags |= S_DEAD;
  	mutex_unlock(&d_inode(dentry)->i_mutex);
  	if (!error)
  		d_delete(dentry);
  
  	return error;
  }
  
  #define xattr_may_create(flags)	(!flags || flags & XATTR_CREATE)
  
  static struct dentry *open_xa_root(struct super_block *sb, int flags)
  {
  	struct dentry *privroot = REISERFS_SB(sb)->priv_root;
  	struct dentry *xaroot;
  
  	if (d_really_is_negative(privroot))
  		return ERR_PTR(-ENODATA);
  
  	mutex_lock_nested(&d_inode(privroot)->i_mutex, I_MUTEX_XATTR);
  
  	xaroot = dget(REISERFS_SB(sb)->xattr_root);
  	if (!xaroot)
  		xaroot = ERR_PTR(-ENODATA);
  	else if (d_really_is_negative(xaroot)) {
  		int err = -ENODATA;
  
  		if (xattr_may_create(flags))
  			err = xattr_mkdir(d_inode(privroot), xaroot, 0700);
  		if (err) {
  			dput(xaroot);
  			xaroot = ERR_PTR(err);
  		}
  	}
  
  	mutex_unlock(&d_inode(privroot)->i_mutex);
  	return xaroot;
  }
  
  static struct dentry *open_xa_dir(const struct inode *inode, int flags)
  {
  	struct dentry *xaroot, *xadir;
  	char namebuf[17];
  
  	xaroot = open_xa_root(inode->i_sb, flags);
  	if (IS_ERR(xaroot))
  		return xaroot;
  
  	snprintf(namebuf, sizeof(namebuf), "%X.%X",
  		 le32_to_cpu(INODE_PKEY(inode)->k_objectid),
  		 inode->i_generation);
  
  	mutex_lock_nested(&d_inode(xaroot)->i_mutex, I_MUTEX_XATTR);
  
  	xadir = lookup_one_len(namebuf, xaroot, strlen(namebuf));
  	if (!IS_ERR(xadir) && d_really_is_negative(xadir)) {
  		int err = -ENODATA;
  
  		if (xattr_may_create(flags))
  			err = xattr_mkdir(d_inode(xaroot), xadir, 0700);
  		if (err) {
  			dput(xadir);
  			xadir = ERR_PTR(err);
  		}
  	}
  
  	mutex_unlock(&d_inode(xaroot)->i_mutex);
  	dput(xaroot);
  	return xadir;
  }
  
  /*
   * The following are side effects of other operations that aren't explicitly
   * modifying extended attributes. This includes operations such as permissions
   * or ownership changes, object deletions, etc.
   */
  struct reiserfs_dentry_buf {
  	struct dir_context ctx;
  	struct dentry *xadir;
  	int count;
  	struct dentry *dentries[8];
  };
  
  static int
  fill_with_dentries(struct dir_context *ctx, const char *name, int namelen,
  		   loff_t offset, u64 ino, unsigned int d_type)
  {
  	struct reiserfs_dentry_buf *dbuf =
  		container_of(ctx, struct reiserfs_dentry_buf, ctx);
  	struct dentry *dentry;
  
  	WARN_ON_ONCE(!mutex_is_locked(&d_inode(dbuf->xadir)->i_mutex));
  
  	if (dbuf->count == ARRAY_SIZE(dbuf->dentries))
  		return -ENOSPC;
  
  	if (name[0] == '.' && (namelen < 2 ||
  			       (namelen == 2 && name[1] == '.')))
  		return 0;
  
  	dentry = lookup_one_len(name, dbuf->xadir, namelen);
  	if (IS_ERR(dentry)) {
  		return PTR_ERR(dentry);
  	} else if (d_really_is_negative(dentry)) {
  		/* A directory entry exists, but no file? */
  		reiserfs_error(dentry->d_sb, "xattr-20003",
  			       "Corrupted directory: xattr %pd listed but "
  			       "not found for file %pd.\n",
  			       dentry, dbuf->xadir);
  		dput(dentry);
  		return -EIO;
  	}
  
  	dbuf->dentries[dbuf->count++] = dentry;
  	return 0;
  }
  
  static void
  cleanup_dentry_buf(struct reiserfs_dentry_buf *buf)
  {
  	int i;
  
  	for (i = 0; i < buf->count; i++)
  		if (buf->dentries[i])
  			dput(buf->dentries[i]);
  }
  
  static int reiserfs_for_each_xattr(struct inode *inode,
  				   int (*action)(struct dentry *, void *),
  				   void *data)
  {
  	struct dentry *dir;
  	int i, err = 0;
  	struct reiserfs_dentry_buf buf = {
  		.ctx.actor = fill_with_dentries,
  	};
  
  	/* Skip out, an xattr has no xattrs associated with it */
  	if (IS_PRIVATE(inode) || get_inode_sd_version(inode) == STAT_DATA_V1)
  		return 0;
  
  	dir = open_xa_dir(inode, XATTR_REPLACE);
  	if (IS_ERR(dir)) {
  		err = PTR_ERR(dir);
  		goto out;
  	} else if (d_really_is_negative(dir)) {
  		err = 0;
  		goto out_dir;
  	}
  
  	mutex_lock_nested(&d_inode(dir)->i_mutex, I_MUTEX_XATTR);
  
  	buf.xadir = dir;
  	while (1) {
  		err = reiserfs_readdir_inode(d_inode(dir), &buf.ctx);
  		if (err)
  			break;
  		if (!buf.count)
  			break;
  		for (i = 0; !err && i < buf.count && buf.dentries[i]; i++) {
  			struct dentry *dentry = buf.dentries[i];
  
  			if (!d_is_dir(dentry))
  				err = action(dentry, data);
  
  			dput(dentry);
  			buf.dentries[i] = NULL;
  		}
  		if (err)
  			break;
  		buf.count = 0;
  	}
  	mutex_unlock(&d_inode(dir)->i_mutex);
  
  	cleanup_dentry_buf(&buf);
  
  	if (!err) {
  		/*
  		 * We start a transaction here to avoid a ABBA situation
  		 * between the xattr root's i_mutex and the journal lock.
  		 * This doesn't incur much additional overhead since the
  		 * new transaction will just nest inside the
  		 * outer transaction.
  		 */
  		int blocks = JOURNAL_PER_BALANCE_CNT * 2 + 2 +
  			     4 * REISERFS_QUOTA_TRANS_BLOCKS(inode->i_sb);
  		struct reiserfs_transaction_handle th;
  
  		reiserfs_write_lock(inode->i_sb);
  		err = journal_begin(&th, inode->i_sb, blocks);
  		reiserfs_write_unlock(inode->i_sb);
  		if (!err) {
  			int jerror;
  
  			mutex_lock_nested(&d_inode(dir->d_parent)->i_mutex,
  					  I_MUTEX_XATTR);
  			err = action(dir, data);
  			reiserfs_write_lock(inode->i_sb);
  			jerror = journal_end(&th);
  			reiserfs_write_unlock(inode->i_sb);
  			mutex_unlock(&d_inode(dir->d_parent)->i_mutex);
  			err = jerror ?: err;
  		}
  	}
  out_dir:
  	dput(dir);
  out:
  	/* -ENODATA isn't an error */
  	if (err == -ENODATA)
  		err = 0;
  	return err;
  }
  
  static int delete_one_xattr(struct dentry *dentry, void *data)
  {
  	struct inode *dir = d_inode(dentry->d_parent);
  
  	/* This is the xattr dir, handle specially. */
  	if (d_is_dir(dentry))
  		return xattr_rmdir(dir, dentry);
  
  	return xattr_unlink(dir, dentry);
  }
  
  static int chown_one_xattr(struct dentry *dentry, void *data)
  {
  	struct iattr *attrs = data;
  	int ia_valid = attrs->ia_valid;
  	int err;
  
  	/*
  	 * We only want the ownership bits. Otherwise, we'll do
  	 * things like change a directory to a regular file if
  	 * ATTR_MODE is set.
  	 */
  	attrs->ia_valid &= (ATTR_UID|ATTR_GID);
  	err = reiserfs_setattr(dentry, attrs);
  	attrs->ia_valid = ia_valid;
  
  	return err;
  }
  
  /* No i_mutex, but the inode is unconnected. */
  int reiserfs_delete_xattrs(struct inode *inode)
  {
  	int err = reiserfs_for_each_xattr(inode, delete_one_xattr, NULL);
  
  	if (err)
  		reiserfs_warning(inode->i_sb, "jdm-20004",
  				 "Couldn't delete all xattrs (%d)\n", err);
  	return err;
  }
  
  /* inode->i_mutex: down */
  int reiserfs_chown_xattrs(struct inode *inode, struct iattr *attrs)
  {
  	int err = reiserfs_for_each_xattr(inode, chown_one_xattr, attrs);
  
  	if (err)
  		reiserfs_warning(inode->i_sb, "jdm-20007",
  				 "Couldn't chown all xattrs (%d)\n", err);
  	return err;
  }
  
  #ifdef CONFIG_REISERFS_FS_XATTR
  /*
   * Returns a dentry corresponding to a specific extended attribute file
   * for the inode. If flags allow, the file is created. Otherwise, a
   * valid or negative dentry, or an error is returned.
   */
  static struct dentry *xattr_lookup(struct inode *inode, const char *name,
  				    int flags)
  {
  	struct dentry *xadir, *xafile;
  	int err = 0;
  
  	xadir = open_xa_dir(inode, flags);
  	if (IS_ERR(xadir))
  		return ERR_CAST(xadir);
  
  	mutex_lock_nested(&d_inode(xadir)->i_mutex, I_MUTEX_XATTR);
  	xafile = lookup_one_len(name, xadir, strlen(name));
  	if (IS_ERR(xafile)) {
  		err = PTR_ERR(xafile);
  		goto out;
  	}
  
  	if (d_really_is_positive(xafile) && (flags & XATTR_CREATE))
  		err = -EEXIST;
  
  	if (d_really_is_negative(xafile)) {
  		err = -ENODATA;
  		if (xattr_may_create(flags))
  			err = xattr_create(d_inode(xadir), xafile,
  					      0700|S_IFREG);
  	}
  
  	if (err)
  		dput(xafile);
  out:
  	mutex_unlock(&d_inode(xadir)->i_mutex);
  	dput(xadir);
  	if (err)
  		return ERR_PTR(err);
  	return xafile;
  }
  
  /* Internal operations on file data */
  static inline void reiserfs_put_page(struct page *page)
  {
  	kunmap(page);
  	page_cache_release(page);
  }
  
  static struct page *reiserfs_get_page(struct inode *dir, size_t n)
  {
  	struct address_space *mapping = dir->i_mapping;
  	struct page *page;
  	/*
  	 * We can deadlock if we try to free dentries,
  	 * and an unlink/rmdir has just occurred - GFP_NOFS avoids this
  	 */
  	mapping_set_gfp_mask(mapping, GFP_NOFS);
  	page = read_mapping_page(mapping, n >> PAGE_CACHE_SHIFT, NULL);
  	if (!IS_ERR(page)) {
  		kmap(page);
  		if (PageError(page))
  			goto fail;
  	}
  	return page;
  
  fail:
  	reiserfs_put_page(page);
  	return ERR_PTR(-EIO);
  }
  
  static inline __u32 xattr_hash(const char *msg, int len)
  {
  	return csum_partial(msg, len, 0);
  }
  
  int reiserfs_commit_write(struct file *f, struct page *page,
  			  unsigned from, unsigned to);
  
  static void update_ctime(struct inode *inode)
  {
  	struct timespec now = current_fs_time(inode->i_sb);
  
  	if (inode_unhashed(inode) || !inode->i_nlink ||
  	    timespec_equal(&inode->i_ctime, &now))
  		return;
  
  	inode->i_ctime = CURRENT_TIME_SEC;
  	mark_inode_dirty(inode);
  }
  
  static int lookup_and_delete_xattr(struct inode *inode, const char *name)
  {
  	int err = 0;
  	struct dentry *dentry, *xadir;
  
  	xadir = open_xa_dir(inode, XATTR_REPLACE);
  	if (IS_ERR(xadir))
  		return PTR_ERR(xadir);
  
  	mutex_lock_nested(&d_inode(xadir)->i_mutex, I_MUTEX_XATTR);
  	dentry = lookup_one_len(name, xadir, strlen(name));
  	if (IS_ERR(dentry)) {
  		err = PTR_ERR(dentry);
  		goto out_dput;
  	}
  
  	if (d_really_is_positive(dentry)) {
  		err = xattr_unlink(d_inode(xadir), dentry);
  		update_ctime(inode);
  	}
  
  	dput(dentry);
  out_dput:
  	mutex_unlock(&d_inode(xadir)->i_mutex);
  	dput(xadir);
  	return err;
  }
  
  
  /* Generic extended attribute operations that can be used by xa plugins */
  
  /*
   * inode->i_mutex: down
   */
  int
  reiserfs_xattr_set_handle(struct reiserfs_transaction_handle *th,
  			  struct inode *inode, const char *name,
  			  const void *buffer, size_t buffer_size, int flags)
  {
  	int err = 0;
  	struct dentry *dentry;
  	struct page *page;
  	char *data;
  	size_t file_pos = 0;
  	size_t buffer_pos = 0;
  	size_t new_size;
  	__u32 xahash = 0;
  
  	if (get_inode_sd_version(inode) == STAT_DATA_V1)
  		return -EOPNOTSUPP;
  
  	if (!buffer) {
  		err = lookup_and_delete_xattr(inode, name);
  		return err;
  	}
  
  	dentry = xattr_lookup(inode, name, flags);
  	if (IS_ERR(dentry))
  		return PTR_ERR(dentry);
  
  	down_write(&REISERFS_I(inode)->i_xattr_sem);
  
  	xahash = xattr_hash(buffer, buffer_size);
  	while (buffer_pos < buffer_size || buffer_pos == 0) {
  		size_t chunk;
  		size_t skip = 0;
  		size_t page_offset = (file_pos & (PAGE_CACHE_SIZE - 1));
  
  		if (buffer_size - buffer_pos > PAGE_CACHE_SIZE)
  			chunk = PAGE_CACHE_SIZE;
  		else
  			chunk = buffer_size - buffer_pos;
  
  		page = reiserfs_get_page(d_inode(dentry), file_pos);
  		if (IS_ERR(page)) {
  			err = PTR_ERR(page);
  			goto out_unlock;
  		}
  
  		lock_page(page);
  		data = page_address(page);
  
  		if (file_pos == 0) {
  			struct reiserfs_xattr_header *rxh;
  
  			skip = file_pos = sizeof(struct reiserfs_xattr_header);
  			if (chunk + skip > PAGE_CACHE_SIZE)
  				chunk = PAGE_CACHE_SIZE - skip;
  			rxh = (struct reiserfs_xattr_header *)data;
  			rxh->h_magic = cpu_to_le32(REISERFS_XATTR_MAGIC);
  			rxh->h_hash = cpu_to_le32(xahash);
  		}
  
  		reiserfs_write_lock(inode->i_sb);
  		err = __reiserfs_write_begin(page, page_offset, chunk + skip);
  		if (!err) {
  			if (buffer)
  				memcpy(data + skip, buffer + buffer_pos, chunk);
  			err = reiserfs_commit_write(NULL, page, page_offset,
  						    page_offset + chunk +
  						    skip);
  		}
  		reiserfs_write_unlock(inode->i_sb);
  		unlock_page(page);
  		reiserfs_put_page(page);
  		buffer_pos += chunk;
  		file_pos += chunk;
  		skip = 0;
  		if (err || buffer_size == 0 || !buffer)
  			break;
  	}
  
  	new_size = buffer_size + sizeof(struct reiserfs_xattr_header);
  	if (!err && new_size < i_size_read(d_inode(dentry))) {
  		struct iattr newattrs = {
  			.ia_ctime = current_fs_time(inode->i_sb),
  			.ia_size = new_size,
  			.ia_valid = ATTR_SIZE | ATTR_CTIME,
  		};
  
  		mutex_lock_nested(&d_inode(dentry)->i_mutex, I_MUTEX_XATTR);
  		inode_dio_wait(d_inode(dentry));
  
  		err = reiserfs_setattr(dentry, &newattrs);
  		mutex_unlock(&d_inode(dentry)->i_mutex);
  	} else
  		update_ctime(inode);
  out_unlock:
  	up_write(&REISERFS_I(inode)->i_xattr_sem);
  	dput(dentry);
  	return err;
  }
  
  /* We need to start a transaction to maintain lock ordering */
  int reiserfs_xattr_set(struct inode *inode, const char *name,
  		       const void *buffer, size_t buffer_size, int flags)
  {
  
  	struct reiserfs_transaction_handle th;
  	int error, error2;
  	size_t jbegin_count = reiserfs_xattr_nblocks(inode, buffer_size);
  
  	if (!(flags & XATTR_REPLACE))
  		jbegin_count += reiserfs_xattr_jcreate_nblocks(inode);
  
  	reiserfs_write_lock(inode->i_sb);
  	error = journal_begin(&th, inode->i_sb, jbegin_count);
  	reiserfs_write_unlock(inode->i_sb);
  	if (error) {
  		return error;
  	}
  
  	error = reiserfs_xattr_set_handle(&th, inode, name,
  					  buffer, buffer_size, flags);
  
  	reiserfs_write_lock(inode->i_sb);
  	error2 = journal_end(&th);
  	reiserfs_write_unlock(inode->i_sb);
  	if (error == 0)
  		error = error2;
  
  	return error;
  }
  
  /*
   * inode->i_mutex: down
   */
  int
  reiserfs_xattr_get(struct inode *inode, const char *name, void *buffer,
  		   size_t buffer_size)
  {
  	ssize_t err = 0;
  	struct dentry *dentry;
  	size_t isize;
  	size_t file_pos = 0;
  	size_t buffer_pos = 0;
  	struct page *page;
  	__u32 hash = 0;
  
  	if (name == NULL)
  		return -EINVAL;
  
  	/*
  	 * We can't have xattrs attached to v1 items since they don't have
  	 * generation numbers
  	 */
  	if (get_inode_sd_version(inode) == STAT_DATA_V1)
  		return -EOPNOTSUPP;
  
  	dentry = xattr_lookup(inode, name, XATTR_REPLACE);
  	if (IS_ERR(dentry)) {
  		err = PTR_ERR(dentry);
  		goto out;
  	}
  
  	down_read(&REISERFS_I(inode)->i_xattr_sem);
  
  	isize = i_size_read(d_inode(dentry));
  
  	/* Just return the size needed */
  	if (buffer == NULL) {
  		err = isize - sizeof(struct reiserfs_xattr_header);
  		goto out_unlock;
  	}
  
  	if (buffer_size < isize - sizeof(struct reiserfs_xattr_header)) {
  		err = -ERANGE;
  		goto out_unlock;
  	}
  
  	while (file_pos < isize) {
  		size_t chunk;
  		char *data;
  		size_t skip = 0;
  
  		if (isize - file_pos > PAGE_CACHE_SIZE)
  			chunk = PAGE_CACHE_SIZE;
  		else
  			chunk = isize - file_pos;
  
  		page = reiserfs_get_page(d_inode(dentry), file_pos);
  		if (IS_ERR(page)) {
  			err = PTR_ERR(page);
  			goto out_unlock;
  		}
  
  		lock_page(page);
  		data = page_address(page);
  		if (file_pos == 0) {
  			struct reiserfs_xattr_header *rxh =
  			    (struct reiserfs_xattr_header *)data;
  			skip = file_pos = sizeof(struct reiserfs_xattr_header);
  			chunk -= skip;
  			/* Magic doesn't match up.. */
  			if (rxh->h_magic != cpu_to_le32(REISERFS_XATTR_MAGIC)) {
  				unlock_page(page);
  				reiserfs_put_page(page);
  				reiserfs_warning(inode->i_sb, "jdm-20001",
  						 "Invalid magic for xattr (%s) "
  						 "associated with %k", name,
  						 INODE_PKEY(inode));
  				err = -EIO;
  				goto out_unlock;
  			}
  			hash = le32_to_cpu(rxh->h_hash);
  		}
  		memcpy(buffer + buffer_pos, data + skip, chunk);
  		unlock_page(page);
  		reiserfs_put_page(page);
  		file_pos += chunk;
  		buffer_pos += chunk;
  		skip = 0;
  	}
  	err = isize - sizeof(struct reiserfs_xattr_header);
  
  	if (xattr_hash(buffer, isize - sizeof(struct reiserfs_xattr_header)) !=
  	    hash) {
  		reiserfs_warning(inode->i_sb, "jdm-20002",
  				 "Invalid hash for xattr (%s) associated "
  				 "with %k", name, INODE_PKEY(inode));
  		err = -EIO;
  	}
  
  out_unlock:
  	up_read(&REISERFS_I(inode)->i_xattr_sem);
  	dput(dentry);
  
  out:
  	return err;
  }
  
  /*
   * In order to implement different sets of xattr operations for each xattr
   * prefix with the generic xattr API, a filesystem should create a
   * null-terminated array of struct xattr_handler (one for each prefix) and
   * hang a pointer to it off of the s_xattr field of the superblock.
   *
   * The generic_fooxattr() functions will use this list to dispatch xattr
   * operations to the correct xattr_handler.
   */
  #define for_each_xattr_handler(handlers, handler)		\
  		for ((handler) = *(handlers)++;			\
  			(handler) != NULL;			\
  			(handler) = *(handlers)++)
  
  /* This is the implementation for the xattr plugin infrastructure */
  static inline const struct xattr_handler *
  find_xattr_handler_prefix(const struct xattr_handler **handlers,
  			   const char *name)
  {
  	const struct xattr_handler *xah;
  
  	if (!handlers)
  		return NULL;
  
  	for_each_xattr_handler(handlers, xah) {
  		if (strncmp(xah->prefix, name, strlen(xah->prefix)) == 0)
  			break;
  	}
  
  	return xah;
  }
  
  
  /*
   * Inode operation getxattr()
   */
  ssize_t
  reiserfs_getxattr(struct dentry * dentry, const char *name, void *buffer,
  		  size_t size)
  {
  	const struct xattr_handler *handler;
  
  	handler = find_xattr_handler_prefix(dentry->d_sb->s_xattr, name);
  
  	if (!handler || get_inode_sd_version(d_inode(dentry)) == STAT_DATA_V1)
  		return -EOPNOTSUPP;
  
  	return handler->get(handler, dentry, name, buffer, size);
  }
  
  /*
   * Inode operation setxattr()
   *
   * d_inode(dentry)->i_mutex down
   */
  int
  reiserfs_setxattr(struct dentry *dentry, const char *name, const void *value,
  		  size_t size, int flags)
  {
  	const struct xattr_handler *handler;
  
  	handler = find_xattr_handler_prefix(dentry->d_sb->s_xattr, name);
  
  	if (!handler || get_inode_sd_version(d_inode(dentry)) == STAT_DATA_V1)
  		return -EOPNOTSUPP;
  
  	return handler->set(handler, dentry, name, value, size, flags);
  }
  
  /*
   * Inode operation removexattr()
   *
   * d_inode(dentry)->i_mutex down
   */
  int reiserfs_removexattr(struct dentry *dentry, const char *name)
  {
  	const struct xattr_handler *handler;
  
  	handler = find_xattr_handler_prefix(dentry->d_sb->s_xattr, name);
  
  	if (!handler || get_inode_sd_version(d_inode(dentry)) == STAT_DATA_V1)
  		return -EOPNOTSUPP;
  
  	return handler->set(handler, dentry, name, NULL, 0, XATTR_REPLACE);
  }
  
  struct listxattr_buf {
  	struct dir_context ctx;
  	size_t size;
  	size_t pos;
  	char *buf;
  	struct dentry *dentry;
  };
  
  static int listxattr_filler(struct dir_context *ctx, const char *name,
  			    int namelen, loff_t offset, u64 ino,
  			    unsigned int d_type)
  {
  	struct listxattr_buf *b =
  		container_of(ctx, struct listxattr_buf, ctx);
  	size_t size;
  
  	if (name[0] != '.' ||
  	    (namelen != 1 && (name[1] != '.' || namelen != 2))) {
  		const struct xattr_handler *handler;
  
  		handler = find_xattr_handler_prefix(b->dentry->d_sb->s_xattr,
  						    name);
  		if (!handler)	/* Unsupported xattr name */
  			return 0;
  		if (b->buf) {
  			size = handler->list(handler, b->dentry,
  					     b->buf + b->pos, b->size, name,
  					     namelen);
  			if (size > b->size)
  				return -ERANGE;
  		} else {
  			size = handler->list(handler, b->dentry,
  					     NULL, 0, name, namelen);
  		}
  
  		b->pos += size;
  	}
  	return 0;
  }
  
  /*
   * Inode operation listxattr()
   *
   * We totally ignore the generic listxattr here because it would be stupid
   * not to. Since the xattrs are organized in a directory, we can just
   * readdir to find them.
   */
  ssize_t reiserfs_listxattr(struct dentry * dentry, char *buffer, size_t size)
  {
  	struct dentry *dir;
  	int err = 0;
  	struct listxattr_buf buf = {
  		.ctx.actor = listxattr_filler,
  		.dentry = dentry,
  		.buf = buffer,
  		.size = buffer ? size : 0,
  	};
  
  	if (d_really_is_negative(dentry))
  		return -EINVAL;
  
  	if (!dentry->d_sb->s_xattr ||
  	    get_inode_sd_version(d_inode(dentry)) == STAT_DATA_V1)
  		return -EOPNOTSUPP;
  
  	dir = open_xa_dir(d_inode(dentry), XATTR_REPLACE);
  	if (IS_ERR(dir)) {
  		err = PTR_ERR(dir);
  		if (err == -ENODATA)
  			err = 0;  /* Not an error if there aren't any xattrs */
  		goto out;
  	}
  
  	mutex_lock_nested(&d_inode(dir)->i_mutex, I_MUTEX_XATTR);
  	err = reiserfs_readdir_inode(d_inode(dir), &buf.ctx);
  	mutex_unlock(&d_inode(dir)->i_mutex);
  
  	if (!err)
  		err = buf.pos;
  
  	dput(dir);
  out:
  	return err;
  }
  
  static int create_privroot(struct dentry *dentry)
  {
  	int err;
  	struct inode *inode = d_inode(dentry->d_parent);
  
  	WARN_ON_ONCE(!mutex_is_locked(&inode->i_mutex));
  
  	err = xattr_mkdir(inode, dentry, 0700);
  	if (err || d_really_is_negative(dentry)) {
  		reiserfs_warning(dentry->d_sb, "jdm-20006",
  				 "xattrs/ACLs enabled and couldn't "
  				 "find/create .reiserfs_priv. "
  				 "Failing mount.");
  		return -EOPNOTSUPP;
  	}
  
  	d_inode(dentry)->i_flags |= S_PRIVATE;
  	reiserfs_info(dentry->d_sb, "Created %s - reserved for xattr "
  		      "storage.\n", PRIVROOT_NAME);
  
  	return 0;
  }
  
  #else
  int __init reiserfs_xattr_register_handlers(void) { return 0; }
  void reiserfs_xattr_unregister_handlers(void) {}
  static int create_privroot(struct dentry *dentry) { return 0; }
  #endif
  
  /* Actual operations that are exported to VFS-land */
  static const struct xattr_handler *reiserfs_xattr_handlers[] = {
  #ifdef CONFIG_REISERFS_FS_XATTR
  	&reiserfs_xattr_user_handler,
  	&reiserfs_xattr_trusted_handler,
  #endif
  #ifdef CONFIG_REISERFS_FS_SECURITY
  	&reiserfs_xattr_security_handler,
  #endif
  #ifdef CONFIG_REISERFS_FS_POSIX_ACL
  	&posix_acl_access_xattr_handler,
  	&posix_acl_default_xattr_handler,
  #endif
  	NULL
  };
  
  static int xattr_mount_check(struct super_block *s)
  {
  	/*
  	 * We need generation numbers to ensure that the oid mapping is correct
  	 * v3.5 filesystems don't have them.
  	 */
  	if (old_format_only(s)) {
  		if (reiserfs_xattrs_optional(s)) {
  			/*
  			 * Old format filesystem, but optional xattrs have
  			 * been enabled. Error out.
  			 */
  			reiserfs_warning(s, "jdm-2005",
  					 "xattrs/ACLs not supported "
  					 "on pre-v3.6 format filesystems. "
  					 "Failing mount.");
  			return -EOPNOTSUPP;
  		}
  	}
  
  	return 0;
  }
  
  int reiserfs_permission(struct inode *inode, int mask)
  {
  	/*
  	 * We don't do permission checks on the internal objects.
  	 * Permissions are determined by the "owning" object.
  	 */
  	if (IS_PRIVATE(inode))
  		return 0;
  
  	return generic_permission(inode, mask);
  }
  
  static int xattr_hide_revalidate(struct dentry *dentry, unsigned int flags)
  {
  	return -EPERM;
  }
  
  static const struct dentry_operations xattr_lookup_poison_ops = {
  	.d_revalidate = xattr_hide_revalidate,
  };
  
  int reiserfs_lookup_privroot(struct super_block *s)
  {
  	struct dentry *dentry;
  	int err = 0;
  
  	/* If we don't have the privroot located yet - go find it */
  	mutex_lock(&d_inode(s->s_root)->i_mutex);
  	dentry = lookup_one_len(PRIVROOT_NAME, s->s_root,
  				strlen(PRIVROOT_NAME));
  	if (!IS_ERR(dentry)) {
  		REISERFS_SB(s)->priv_root = dentry;
  		d_set_d_op(dentry, &xattr_lookup_poison_ops);
  		if (d_really_is_positive(dentry))
  			d_inode(dentry)->i_flags |= S_PRIVATE;
  	} else
  		err = PTR_ERR(dentry);
  	mutex_unlock(&d_inode(s->s_root)->i_mutex);
  
  	return err;
  }
  
  /*
   * We need to take a copy of the mount flags since things like
   * MS_RDONLY don't get set until *after* we're called.
   * mount_flags != mount_options
   */
  int reiserfs_xattr_init(struct super_block *s, int mount_flags)
  {
  	int err = 0;
  	struct dentry *privroot = REISERFS_SB(s)->priv_root;
  
  	err = xattr_mount_check(s);
  	if (err)
  		goto error;
  
  	if (d_really_is_negative(privroot) && !(mount_flags & MS_RDONLY)) {
  		mutex_lock(&d_inode(s->s_root)->i_mutex);
  		err = create_privroot(REISERFS_SB(s)->priv_root);
  		mutex_unlock(&d_inode(s->s_root)->i_mutex);
  	}
  
  	if (d_really_is_positive(privroot)) {
  		s->s_xattr = reiserfs_xattr_handlers;
  		mutex_lock(&d_inode(privroot)->i_mutex);
  		if (!REISERFS_SB(s)->xattr_root) {
  			struct dentry *dentry;
  
  			dentry = lookup_one_len(XAROOT_NAME, privroot,
  						strlen(XAROOT_NAME));
  			if (!IS_ERR(dentry))
  				REISERFS_SB(s)->xattr_root = dentry;
  			else
  				err = PTR_ERR(dentry);
  		}
  		mutex_unlock(&d_inode(privroot)->i_mutex);
  	}
  
  error:
  	if (err) {
  		clear_bit(REISERFS_XATTRS_USER, &REISERFS_SB(s)->s_mount_opt);
  		clear_bit(REISERFS_POSIXACL, &REISERFS_SB(s)->s_mount_opt);
  	}
  
  	/* The super_block MS_POSIXACL must mirror the (no)acl mount option. */
  	if (reiserfs_posixacl(s))
  		s->s_flags |= MS_POSIXACL;
  	else
  		s->s_flags &= ~MS_POSIXACL;
  
  	return err;
  }
  