[PATCH v2 01/13] VFS permit cross device vfs_copy_file_range

From: Olga Kornievskaia <olga.kornievskaia@gmail.com>
To: trond.myklebust@hammerspace.com, anna.schumaker@netapp.com,
	viro@zeniv.linux.org.uk, smfrench@gmail.com, miklos@szeredi.hu
Cc: linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-cifs@vger.kernel.org, linux-unionfs@vger.kernel.org,
	linux-man@vger.kernel.org
Subject: [PATCH v2 01/13] VFS permit cross device vfs_copy_file_range
Date: Wed, 24 Oct 2018 15:58:24 -0400	[thread overview]
Message-ID: <20181024195837.35532-2-olga.kornievskaia@gmail.com> (raw)
In-Reply-To: <20181024195837.35532-1-olga.kornievskaia@gmail.com>

From: Olga Kornievskaia <kolga@netapp.com>

This patch removes the check for source and destination files to
come from the same superblock. This feature was of interest to
NFS as well as CIFS communities.

Specifically, this feature is needed to allow for NFSv4.2 copy offload
to be done between different NFSv4.2 servers. SMBv3 copy offload between
different servers would be able to use this as well.

Removal of the check implies that passed in source and destination
files can come from different superblocks of the same file system
type or different. It is upto each individual copy_file_range()
file system implementation to decide what type of copy it is
capable of doing and return -EXDEV in cases support is lacking.

There are 3 known implementator of copy_file_range() f_op: NFS,
CIFS, OverlayFS. NFS and CIFS are interested to support cross-device
copy offload but do not support cross file system types copy offload.
Following patches will add appropriate checks in each of the drivers.

If the copy_file_range() errors with EXDEV, the code would fallback
on doing do_splice_direct() copying which in itself is beneficial.

Adding wording to the vfs.txt and porting documentation about the
new support for cross-device copy offload.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
---
 Documentation/filesystems/porting | 7 +++++++
 Documentation/filesystems/vfs.txt | 6 +++++-
 fs/read_write.c                   | 9 +++------
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index 7b7b845..ebb4954 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -622,3 +622,10 @@ in your dentry operations instead.
 	alloc_file_clone(file, flags, ops) does not affect any caller's references.
 	On success you get a new struct file sharing the mount/dentry with the
 	original, on failure - ERR_PTR().
+--
+[mandatory]
+	->copy_file_range() may now be passed files which belong to two
+	different superblocks of the same file system type or which belong
+	to two different filesystems types all together. As before, the
+        destination's copy_file_range() is the function which is called.
+	If it cannot copy ranges from the source, it should return -EXDEV.
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index a6c6a8a..34c0e8c 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -1,5 +1,6 @@
 
 	      Overview of the Linux Virtual File System
+- [fs] nfs: Don't let readdirplus revalidate an inode that was marked as stale (Benjamin Coddington) [1429514 1416532]
 
 	Original author: Richard Gooch <rgooch@atnf.csiro.au>
 
@@ -958,7 +959,10 @@ otherwise noted.
 
   fallocate: called by the VFS to preallocate blocks or punch a hole.
 
-  copy_file_range: called by the copy_file_range(2) system call.
+  copy_file_range: called by copy_file_range(2) system call. This method
+		   works on two file descriptors that might reside on
+		   different superblocks which might belong to file systems
+		   of different types.
 
   clone_file_range: called by the ioctl(2) system call for FICLONERANGE and
 	FICLONE commands.
diff --git a/fs/read_write.c b/fs/read_write.c
index 39b4a21..fb4ffca 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1575,10 +1575,6 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 	    (file_out->f_flags & O_APPEND))
 		return -EBADF;
 
-	/* this could be relaxed once a method supports cross-fs copies */
-	if (inode_in->i_sb != inode_out->i_sb)
-		return -EXDEV;
-
 	if (len == 0)
 		return 0;
 
@@ -1588,7 +1584,8 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 	 * Try cloning first, this is supported by more file systems, and
 	 * more efficient if both clone and copy are supported (e.g. NFS).
 	 */
-	if (file_in->f_op->clone_file_range) {
+	if (inode_in->i_sb == inode_out->i_sb &&
+			file_in->f_op->clone_file_range) {
 		ret = file_in->f_op->clone_file_range(file_in, pos_in,
 				file_out, pos_out, len);
 		if (ret == 0) {
@@ -1600,7 +1597,7 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 	if (file_out->f_op->copy_file_range) {
 		ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out,
 						      pos_out, len, flags);
-		if (ret != -EOPNOTSUPP)
+		if (ret != -EOPNOTSUPP && ret != -EXDEV)
 			goto done;
 	}
 
-- 
1.8.3.1
