vfs: allow vfs_clone_file_range() across mount points

FICLONE/FICLONERANGE ioctls return -EXDEV if src and dest
files are not on the same mount point.
Practically, clone only requires that src and dest files
are on the same file system.

Move the check for same mount point to ioctl handler and keep
only the check for same super block in the vfs helper.

A following patch is going to use the vfs_clone_file_range()
helper in overlayfs to copy up between lower and upper
mount points on the same file system.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/ioctl.c

@@ -223,7 +223,11 @@ static long ioctl_file_clone(struct file *dst_file, unsigned long srcfd,
 
 	if (!src_file.file)
 		return -EBADF;
+	ret = -EXDEV;
+	if (src_file.file->f_path.mnt != dst_file->f_path.mnt)
+		goto fdput;
 	ret = vfs_clone_file_range(src_file.file, off, dst_file, destoff, olen);
+fdput:
 	fdput(src_file);
 	return ret;
 }

fs/read_write.c

@@ -1655,8 +1655,12 @@ int vfs_clone_file_range(struct file *file_in, loff_t pos_in,
 	struct inode *inode_out = file_inode(file_out);
 	int ret;
 
-	if (inode_in->i_sb != inode_out->i_sb ||
-	    file_in->f_path.mnt != file_out->f_path.mnt)
+	/*
+	 * FICLONE/FICLONERANGE ioctls enforce that src and dest files are on
+	 * the same mount. Practically, they only need to be on the same file
+	 * system.
+	 */
+	if (inode_in->i_sb != inode_out->i_sb)
 		return -EXDEV;
 
 	if (S_ISDIR(inode_in->i_mode) || S_ISDIR(inode_out->i_mode))