exportfs: add open method

This allows filesystems such as pidfs to provide their custom open.

Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Amir Goldstein <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: brauner

fs/fhandle.c

@@ -401,6 +401,7 @@ static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
 	long retval = 0;
 	struct path path __free(path_put) = {};
 	struct file *file;
+	const struct export_operations *eops;
 
 	retval = handle_to_path(mountdirfd, ufh, &path, open_flag);
 	if (retval)
@@ -410,7 +411,11 @@ static long do_handle_open(int mountdirfd, struct file_handle __user *ufh,
 	if (fd < 0)
 		return fd;
 
-	file = file_open_root(&path, "", open_flag, 0);
+	eops = path.mnt->mnt_sb->s_export_op;
+	if (eops->open)
+		file = eops->open(&path, open_flag);
+	else
+		file = file_open_root(&path, "", open_flag, 0);
 	if (IS_ERR(file))
 		return PTR_ERR(file);
 

include/linux/exportfs.h

@@ -10,6 +10,7 @@ struct inode;
 struct iomap;
 struct super_block;
 struct vfsmount;
+struct path;
 
 /* limit the handle size to NFSv4 handle size now */
 #define MAX_HANDLE_SZ 128
@@ -225,6 +226,9 @@ struct fid {
  *    is also a directory.  In the event that it cannot be found, or storage
  *    space cannot be allocated, a %ERR_PTR should be returned.
  *
+ * open:
+ *    Allow filesystems to specify a custom open function.
+ *
  * commit_metadata:
  *    @commit_metadata should commit metadata changes to stable storage.
  *
@@ -251,6 +255,7 @@ struct export_operations {
 			  bool write, u32 *device_generation);
 	int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
 			     int nr_iomaps, struct iattr *iattr);
+	struct file * (*open)(struct path *path, unsigned int oflags);
 #define	EXPORT_OP_NOWCC			(0x1) /* don't collect v3 wcc data */
 #define	EXPORT_OP_NOSUBTREECHK		(0x2) /* no subtree checking */
 #define	EXPORT_OP_CLOSE_BEFORE_UNLINK	(0x4) /* close files before unlink */