text: #include <linux/syscalls.h>
  #include <linux/export.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/mount.h>
  #include <linux/namei.h>
  #include <linux/statfs.h>
  #include <linux/security.h>
  #include <linux/uaccess.h>
  #include "internal.h"
  
  static int flags_by_mnt(int mnt_flags)
  {
  	int flags = 0;
  
  	if (mnt_flags & MNT_READONLY)
  		flags |= ST_RDONLY;
  	if (mnt_flags & MNT_NOSUID)
  		flags |= ST_NOSUID;
  	if (mnt_flags & MNT_NODEV)
  		flags |= ST_NODEV;
  	if (mnt_flags & MNT_NOEXEC)
  		flags |= ST_NOEXEC;
  	if (mnt_flags & MNT_NOATIME)
  		flags |= ST_NOATIME;
  	if (mnt_flags & MNT_NODIRATIME)
  		flags |= ST_NODIRATIME;
  	if (mnt_flags & MNT_RELATIME)
  		flags |= ST_RELATIME;
  	return flags;
  }
  
  static int flags_by_sb(int s_flags)
  {
  	int flags = 0;
  	if (s_flags & MS_SYNCHRONOUS)
  		flags |= ST_SYNCHRONOUS;
  	if (s_flags & MS_MANDLOCK)
  		flags |= ST_MANDLOCK;
  	return flags;
  }
  
  static int calculate_f_flags(struct vfsmount *mnt)
  {
  	return ST_VALID | flags_by_mnt(mnt->mnt_flags) |
  		flags_by_sb(mnt->mnt_sb->s_flags);
  }
  
  static int statfs_by_dentry(struct dentry *dentry, struct kstatfs *buf)
  {
  	int retval;
  
  	if (!dentry->d_sb->s_op->statfs)
  		return -ENOSYS;
  
  	memset(buf, 0, sizeof(*buf));
  	retval = security_sb_statfs(dentry);
  	if (retval)
  		return retval;
  	retval = dentry->d_sb->s_op->statfs(dentry, buf);
  	if (retval == 0 && buf->f_frsize == 0)
  		buf->f_frsize = buf->f_bsize;
  	return retval;
  }
  
  int vfs_statfs(struct path *path, struct kstatfs *buf)
  {
  	int error;
  
  	error = statfs_by_dentry(path->dentry, buf);
  	if (!error)
  		buf->f_flags = calculate_f_flags(path->mnt);
  	return error;
  }
  EXPORT_SYMBOL(vfs_statfs);
  
  int user_statfs(const char __user *pathname, struct kstatfs *st)
  {
  	struct path path;
  	int error = user_path_at(AT_FDCWD, pathname, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
  	if (!error) {
  		error = vfs_statfs(&path, st);
  		path_put(&path);
  	}
  	return error;
  }
  
  int fd_statfs(int fd, struct kstatfs *st)
  {
  	struct file *file = fget_raw(fd);
  	int error = -EBADF;
  	if (file) {
  		error = vfs_statfs(&file->f_path, st);
  		fput(file);
  	}
  	return error;
  }
  
  static int do_statfs_native(struct kstatfs *st, struct statfs __user *p)
  {
  	struct statfs buf;
  
  	if (sizeof(buf) == sizeof(*st))
  		memcpy(&buf, st, sizeof(*st));
  	else {
  		if (sizeof buf.f_blocks == 4) {
  			if ((st->f_blocks | st->f_bfree | st->f_bavail |
  			     st->f_bsize | st->f_frsize) &
  			    0xffffffff00000000ULL)
  				return -EOVERFLOW;
  			/*
  			 * f_files and f_ffree may be -1; it's okay to stuff
  			 * that into 32 bits
  			 */
  			if (st->f_files != -1 &&
  			    (st->f_files & 0xffffffff00000000ULL))
  				return -EOVERFLOW;
  			if (st->f_ffree != -1 &&
  			    (st->f_ffree & 0xffffffff00000000ULL))
  				return -EOVERFLOW;
  		}
  
  		buf.f_type = st->f_type;
  		buf.f_bsize = st->f_bsize;
  		buf.f_blocks = st->f_blocks;
  		buf.f_bfree = st->f_bfree;
  		buf.f_bavail = st->f_bavail;
  		buf.f_files = st->f_files;
  		buf.f_ffree = st->f_ffree;
  		buf.f_fsid = st->f_fsid;
  		buf.f_namelen = st->f_namelen;
  		buf.f_frsize = st->f_frsize;
  		buf.f_flags = st->f_flags;
  		memset(buf.f_spare, 0, sizeof(buf.f_spare));
  	}
  	if (copy_to_user(p, &buf, sizeof(buf)))
  		return -EFAULT;
  	return 0;
  }
  
  static int do_statfs64(struct kstatfs *st, struct statfs64 __user *p)
  {
  	struct statfs64 buf;
  	if (sizeof(buf) == sizeof(*st))
  		memcpy(&buf, st, sizeof(*st));
  	else {
  		buf.f_type = st->f_type;
  		buf.f_bsize = st->f_bsize;
  		buf.f_blocks = st->f_blocks;
  		buf.f_bfree = st->f_bfree;
  		buf.f_bavail = st->f_bavail;
  		buf.f_files = st->f_files;
  		buf.f_ffree = st->f_ffree;
  		buf.f_fsid = st->f_fsid;
  		buf.f_namelen = st->f_namelen;
  		buf.f_frsize = st->f_frsize;
  		buf.f_flags = st->f_flags;
  		memset(buf.f_spare, 0, sizeof(buf.f_spare));
  	}
  	if (copy_to_user(p, &buf, sizeof(buf)))
  		return -EFAULT;
  	return 0;
  }
  
  SYSCALL_DEFINE2(statfs, const char __user *, pathname, struct statfs __user *, buf)
  {
  	struct kstatfs st;
  	int error = user_statfs(pathname, &st);
  	if (!error)
  		error = do_statfs_native(&st, buf);
  	return error;
  }
  
  SYSCALL_DEFINE3(statfs64, const char __user *, pathname, size_t, sz, struct statfs64 __user *, buf)
  {
  	struct kstatfs st;
  	int error;
  	if (sz != sizeof(*buf))
  		return -EINVAL;
  	error = user_statfs(pathname, &st);
  	if (!error)
  		error = do_statfs64(&st, buf);
  	return error;
  }
  
  SYSCALL_DEFINE2(fstatfs, unsigned int, fd, struct statfs __user *, buf)
  {
  	struct kstatfs st;
  	int error = fd_statfs(fd, &st);
  	if (!error)
  		error = do_statfs_native(&st, buf);
  	return error;
  }
  
  SYSCALL_DEFINE3(fstatfs64, unsigned int, fd, size_t, sz, struct statfs64 __user *, buf)
  {
  	struct kstatfs st;
  	int error;
  
  	if (sz != sizeof(*buf))
  		return -EINVAL;
  
  	error = fd_statfs(fd, &st);
  	if (!error)
  		error = do_statfs64(&st, buf);
  	return error;
  }
  
  int vfs_ustat(dev_t dev, struct kstatfs *sbuf)
  {
  	struct super_block *s = user_get_super(dev);
  	int err;
  	if (!s)
  		return -EINVAL;
  
  	err = statfs_by_dentry(s->s_root, sbuf);
  	drop_super(s);
  	return err;
  }
  
  SYSCALL_DEFINE2(ustat, unsigned, dev, struct ustat __user *, ubuf)
  {
  	struct ustat tmp;
  	struct kstatfs sbuf;
  	int err = vfs_ustat(new_decode_dev(dev), &sbuf);
  	if (err)
  		return err;
  
  	memset(&tmp,0,sizeof(struct ustat));
  	tmp.f_tfree = sbuf.f_bfree;
  	tmp.f_tinode = sbuf.f_ffree;
  
  	return copy_to_user(ubuf, &tmp, sizeof(struct ustat)) ? -EFAULT : 0;
  }
  