From: Jeff Layton <jlayton@redhat.com>
Date: Tue, 1 Dec 2009 12:05:34 -0500
Subject: [cifs] duplicate data on appending to some samba servers
Message-id: <1259669134-20737-1-git-send-email-jlayton@redhat.com>
Patchwork-id: 21562
O-Subject: [RHEL5.5 PATCH 11/10] BZ#500838: cifs: Duplicate data on appending to
	some Samba servers
Bugzilla: 500838
RH-Acked-by: Peter Staubach <staubach@redhat.com>

From: Steve French <sfrench@us.ibm.com>

A late breaking patch that just recently went upstream. It only
recently became evident as servers with working POSIX CREATE_AND_X
calls are making it into the field. Adding this to the previous set
since no one has reported it yet, but I believe it's a patch that
we need. Original patch description follows:

-----------------------[snip]-------------------------

SMB writes are sent with a starting offset and length. When the server
supports the newer SMB trans2 posix open (rather than using the SMB
NTCreateX) a file can be opened with SMB_O_APPEND flag, and for that
case Samba server assumes that the offset sent in SMBWriteX is unneeded
since the write should go to the end of the file - which can cause
problems if the write was cached (since the beginning part of a
page could be written twice by the client mm).  Jeff suggested that
masking the flag on posix open on the client is easiest for the time
being. Note that recent Samba server also had an unrelated problem with
SMB NTCreateX and append (see samba bugzilla bug number 6898) which
should not affect current Linux clients (unless cifs Unix Extensions
are disabled).

The cifs client did not send the O_APPEND flag on posix open
before 2.6.29 so the fix is unneeded on early kernels.

In the future, for the non-cached case (O_DIRECT, and forcedirectio mounts)
it would be possible and useful to send O_APPEND on posix open (for Windows
case: FILE_APPEND_DATA but not FILE_WRITE_DATA on SMB NTCreateX) but for
cached writes although the vfs sets the offset to end of file it
may fragment a write across pages - so we can't send O_APPEND on
open (could result in sending part of a page twice).

CC: Stable <stable@kernel.org>
Reviewed-by: Shirish Pargaonkar <shirishp@us.ibm.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
index 9698889..a255b18 100644
--- a/fs/cifs/dir.c
+++ b/fs/cifs/dir.c
@@ -166,8 +166,6 @@ int cifs_posix_open(char *full_path, struct inode **pinode,
 		posix_flags |= SMB_O_EXCL;
 	if (oflags & O_TRUNC)
 		posix_flags |= SMB_O_TRUNC;
-	if (oflags & O_APPEND)
-		posix_flags |= SMB_O_APPEND;
 	if (oflags & O_SYNC)
 		posix_flags |= SMB_O_SYNC;
 	if (oflags & O_DIRECTORY)