[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, 7 insertions, 0 deletions

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index da0f4ffa0613..18e84a4e0504 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -95,6 +95,7 @@ struct smb_vol {
         bool local_lease:1; /* check leases only on local system, not remote */
         bool noblocksnd:1;
         bool noautotune:1;
+        bool nostrictsync:1; /* do not force expensive SMBflush on every sync */
         unsigned int rsize;
         unsigned int wsize;
         unsigned int sockopt;
@@ -1274,6 +1275,10 @@ cifs_parse_mount_options(char *options, const char *devname,
                         vol->intr = 0;
                 } else if (strnicmp(data, "intr", 4) == 0) {
                         vol->intr = 1;
+                } else if (strnicmp(data, "nostrictsync", 12) == 0) {
+                        vol->nostrictsync = 1;
+                } else if (strnicmp(data, "strictsync", 10) == 0) {
+                        vol->nostrictsync = 0;
                 } else if (strnicmp(data, "serverino", 7) == 0) {
                         vol->server_ino = 1;
                 } else if (strnicmp(data, "noserverino", 9) == 0) {
@@ -2160,6 +2165,8 @@ static void setup_cifs_sb(struct smb_vol *pvolume_info,
                 cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_UNX_EMUL;
         if (pvolume_info->nobrl)
                 cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_NO_BRL;
+        if (pvolume_info->nostrictsync)
+                cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_NO_SSYNC;
         if (pvolume_info->mand_lock)
                 cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_NOPOSIXBRL;
         if (pvolume_info->cifs_acl)