#include <linux/syscalls.h>
  #include <linux/slab.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/mount.h>
  #include <linux/namei.h>
  #include <linux/exportfs.h>

  #include <linux/fs_struct.h>
  #include <linux/fsnotify.h>

  #include <linux/personality.h>

  #include <asm/uaccess.h>
  #include "internal.h"

  #include "mount.h"

  
  static long do_sys_name_to_handle(struct path *path,
  				  struct file_handle __user *ufh,
  				  int __user *mnt_id)
  {
  	long retval;
  	struct file_handle f_handle;
  	int handle_dwords, handle_bytes;
  	struct file_handle *handle = NULL;
  
  	/*
  	 * We need t make sure wether the file system
  	 * support decoding of the file handle
  	 */

  	if (!path->dentry->d_sb->s_export_op ||
  	    !path->dentry->d_sb->s_export_op->fh_to_dentry)

  		return -EOPNOTSUPP;
  
  	if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle)))
  		return -EFAULT;
  
  	if (f_handle.handle_bytes > MAX_HANDLE_SZ)
  		return -EINVAL;
  
  	handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
  			 GFP_KERNEL);
  	if (!handle)
  		return -ENOMEM;
  
  	/* convert handle size to  multiple of sizeof(u32) */
  	handle_dwords = f_handle.handle_bytes >> 2;
  
  	/* we ask for a non connected handle */
  	retval = exportfs_encode_fh(path->dentry,
  				    (struct fid *)handle->f_handle,
  				    &handle_dwords,  0);
  	handle->handle_type = retval;
  	/* convert handle size to bytes */
  	handle_bytes = handle_dwords * sizeof(u32);
  	handle->handle_bytes = handle_bytes;
  	if ((handle->handle_bytes > f_handle.handle_bytes) ||
  	    (retval == 255) || (retval == -ENOSPC)) {
  		/* As per old exportfs_encode_fh documentation
  		 * we could return ENOSPC to indicate overflow
  		 * But file system returned 255 always. So handle
  		 * both the values
  		 */
  		/*
  		 * set the handle size to zero so we copy only
  		 * non variable part of the file_handle
  		 */
  		handle_bytes = 0;
  		retval = -EOVERFLOW;
  	} else
  		retval = 0;
  	/* copy the mount id */

  	if (copy_to_user(mnt_id, &real_mount(path->mnt)->mnt_id,
  			 sizeof(*mnt_id)) ||

  	    copy_to_user(ufh, handle,
  			 sizeof(struct file_handle) + handle_bytes))
  		retval = -EFAULT;
  	kfree(handle);
  	return retval;
  }
  
  /**
   * sys_name_to_handle_at: convert name to handle
   * @dfd: directory relative to which name is interpreted if not absolute
   * @name: name that should be converted to handle.
   * @handle: resulting file handle
   * @mnt_id: mount id of the file system containing the file
   * @flag: flag value to indicate whether to follow symlink or not
   *
   * @handle->handle_size indicate the space available to store the
   * variable part of the file handle in bytes. If there is not
   * enough space, the field is updated to return the minimum
   * value required.
   */
  SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const char __user *, name,
  		struct file_handle __user *, handle, int __user *, mnt_id,
  		int, flag)
  {
  	struct path path;
  	int lookup_flags;
  	int err;
  
  	if ((flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
  		return -EINVAL;
  
  	lookup_flags = (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0;
  	if (flag & AT_EMPTY_PATH)
  		lookup_flags |= LOOKUP_EMPTY;
  	err = user_path_at(dfd, name, lookup_flags, &path);
  	if (!err) {
  		err = do_sys_name_to_handle(&path, handle, mnt_id);
  		path_put(&path);
  	}
  	return err;
  }

  
  static struct vfsmount *get_vfsmount_from_fd(int fd)
  {
  	struct path path;
  
  	if (fd == AT_FDCWD) {
  		struct fs_struct *fs = current->fs;
  		spin_lock(&fs->lock);
  		path = fs->pwd;
  		mntget(path.mnt);
  		spin_unlock(&fs->lock);
  	} else {
  		int fput_needed;
  		struct file *file = fget_light(fd, &fput_needed);
  		if (!file)
  			return ERR_PTR(-EBADF);
  		path = file->f_path;
  		mntget(path.mnt);
  		fput_light(file, fput_needed);
  	}
  	return path.mnt;
  }
  
  static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
  {
  	return 1;
  }
  
  static int do_handle_to_path(int mountdirfd, struct file_handle *handle,
  			     struct path *path)
  {
  	int retval = 0;
  	int handle_dwords;
  
  	path->mnt = get_vfsmount_from_fd(mountdirfd);
  	if (IS_ERR(path->mnt)) {
  		retval = PTR_ERR(path->mnt);
  		goto out_err;
  	}
  	/* change the handle size to multiple of sizeof(u32) */
  	handle_dwords = handle->handle_bytes >> 2;
  	path->dentry = exportfs_decode_fh(path->mnt,
  					  (struct fid *)handle->f_handle,
  					  handle_dwords, handle->handle_type,
  					  vfs_dentry_acceptable, NULL);
  	if (IS_ERR(path->dentry)) {
  		retval = PTR_ERR(path->dentry);
  		goto out_mnt;
  	}
  	return 0;
  out_mnt:
  	mntput(path->mnt);
  out_err:
  	return retval;
  }
  
  static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
  		   struct path *path)
  {
  	int retval = 0;
  	struct file_handle f_handle;
  	struct file_handle *handle = NULL;
  
  	/*
  	 * With handle we don't look at the execute bit on the
  	 * the directory. Ideally we would like CAP_DAC_SEARCH.
  	 * But we don't have that
  	 */
  	if (!capable(CAP_DAC_READ_SEARCH)) {
  		retval = -EPERM;
  		goto out_err;
  	}
  	if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
  		retval = -EFAULT;
  		goto out_err;
  	}
  	if ((f_handle.handle_bytes > MAX_HANDLE_SZ) ||
  	    (f_handle.handle_bytes == 0)) {
  		retval = -EINVAL;
  		goto out_err;
  	}
  	handle = kmalloc(sizeof(struct file_handle) + f_handle.handle_bytes,
  			 GFP_KERNEL);
  	if (!handle) {
  		retval = -ENOMEM;
  		goto out_err;
  	}
  	/* copy the full handle */
  	if (copy_from_user(handle, ufh,
  			   sizeof(struct file_handle) +
  			   f_handle.handle_bytes)) {
  		retval = -EFAULT;
  		goto out_handle;
  	}
  
  	retval = do_handle_to_path(mountdirfd, handle, path);
  
  out_handle:
  	kfree(handle);
  out_err:
  	return retval;
  }
  
  long do_handle_open(int mountdirfd,
  		    struct file_handle __user *ufh, int open_flag)
  {
  	long retval = 0;
  	struct path path;
  	struct file *file;
  	int fd;
  
  	retval = handle_to_path(mountdirfd, ufh, &path);
  	if (retval)
  		return retval;
  
  	fd = get_unused_fd_flags(open_flag);
  	if (fd < 0) {
  		path_put(&path);
  		return fd;
  	}
  	file = file_open_root(path.dentry, path.mnt, "", open_flag);
  	if (IS_ERR(file)) {
  		put_unused_fd(fd);
  		retval =  PTR_ERR(file);
  	} else {
  		retval = fd;
  		fsnotify_open(file);
  		fd_install(fd, file);
  	}
  	path_put(&path);
  	return retval;
  }
  
  /**
   * sys_open_by_handle_at: Open the file handle
   * @mountdirfd: directory file descriptor
   * @handle: file handle to be opened
   * @flag: open flags.
   *
   * @mountdirfd indicate the directory file descriptor
   * of the mount point. file handle is decoded relative
   * to the vfsmount pointed by the @mountdirfd. @flags
   * value is same as the open(2) flags.
   */
  SYSCALL_DEFINE3(open_by_handle_at, int, mountdirfd,
  		struct file_handle __user *, handle,
  		int, flags)
  {
  	long ret;
  
  	if (force_o_largefile())
  		flags |= O_LARGEFILE;
  
  	ret = do_handle_open(mountdirfd, handle, flags);
  	return ret;
  }