[PATCH v3 1/4] vfs: allow vfs_clone_file_range() across mount points

[Amir Goldstein <amir73il@gmail.com>]

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 code 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>
---
 fs/ioctl.c      | 2 ++
 fs/read_write.c | 8 ++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/ioctl.c b/fs/ioctl.c
index c415668..34d2994 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -223,6 +223,8 @@ static long ioctl_file_clone(struct file *dst_file, unsigned long srcfd,
 
 	if (!src_file.file)
 		return -EBADF;
+	if (src_file.file->f_path.mnt != dst_file->f_path.mnt)
+		return -EXDEV;
 	ret = vfs_clone_file_range(src_file.file, off, dst_file, destoff, olen);
 	fdput(src_file);
 	return ret;
diff --git a/fs/read_write.c b/fs/read_write.c
index 66215a7..9dc6e52 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1628,8 +1628,12 @@ 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 point. 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))
-- 
2.7.4