[CIFS] Add new nostrictsync cifs mount option to avoid slow SMB flush

If this mount option is set, when an application does an
fsync call then the cifs client does not send an SMB Flush
to the server (to force the server to write all dirty data
for this file immediately to disk), although cifs still sends
all dirty (cached) file data to the server and waits for the
server to respond to the write write.  Since SMB Flush can be
very slow, and some servers may be reliable enough (to risk
delaying slightly flushing the data to disk on the server),
turning on this option may be useful to improve performance for
applications that fsync too much, at a small risk of server
crash.  If this mount option is not set, by default cifs will
send an SMB flush request (and wait for a response) on every
fsync call.

Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/cifs/cifs_fs_sb.h b/fs/cifs/cifs_fs_sb.h
index c4c306f7b06f..e9f177bb0658 100644
--- a/fs/cifs/cifs_fs_sb.h
+++ b/fs/cifs/cifs_fs_sb.h
@@ -32,6 +32,7 @@
 #define CIFS_MOUNT_OVERR_GID    0x800 /* override gid returned from server    */
 #define CIFS_MOUNT_DYNPERM      0x1000 /* allow in-memory only mode setting   */
 #define CIFS_MOUNT_NOPOSIXBRL   0x2000 /* mandatory not posix byte range lock */
+#define CIFS_MOUNT_NO_SSYNC     0x4000 /* don't do slow SMBflush on every sync*/
 
 struct cifs_sb_info {
         struct cifsTconInfo *tcon;      /* primary mount */