fs/backing-file.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Common helpers for stackable filesystems and backing files.
   4  *
   5  * Copyright (C) 2023 CTERA Networks.
   6  */
   7
   8 #include <linux/fs.h>
   9 #include <linux/backing-file.h>
  10
  11 #include "internal.h"
  12
  13 /**
  14  * backing_file_open - open a backing file for kernel internal use
  15  * @user_path:  path that the user reuqested to open
  16  * @flags:      open flags
  17  * @real_path:  path of the backing file
  18  * @cred:       credentials for open
  19  *
  20  * Open a backing file for a stackable filesystem (e.g., overlayfs).
  21  * @user_path may be on the stackable filesystem and @real_path on the
  22  * underlying filesystem.  In this case, we want to be able to return the
  23  * @user_path of the stackable filesystem. This is done by embedding the
  24  * returned file into a container structure that also stores the stacked
  25  * file's path, which can be retrieved using backing_file_user_path().
  26  */
  27 struct file *backing_file_open(const struct path *user_path, int flags,
  28                                const struct path *real_path,
  29                                const struct cred *cred)
  30 {
  31         struct file *f;
  32         int error;
  33
  34         f = alloc_empty_backing_file(flags, cred);
  35         if (IS_ERR(f))
  36                 return f;
  37
  38         path_get(user_path);
  39         *backing_file_user_path(f) = *user_path;
  40         error = vfs_open(real_path, f);
  41         if (error) {
  42                 fput(f);
  43                 f = ERR_PTR(error);
  44         }
  45
  46         return f;
  47 }
  48 EXPORT_SYMBOL_GPL(backing_file_open);