Re: [PATCH] fs/cifs: send SMB_COM_FLUSH in cifs_fsync

[Steve French <smfrench@gmail.com>]

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On Sun, Feb 22, 2009 at 3:12 PM, Horst Reiterer
<horst.reiterer@gmail.com> wrote:
> On Sun, 22 Feb 2009, Steve French wrote:
>> Suggestions on what to call such a new mount option?  How about
>> "nostrictfsync"  ?
>
> Sound good, should be self-explanatory for Samba users and those familiar
> with the fsync concept.
>
> Horst.

Patch attached for nostrictfsync cifs mount option



-- 
Thanks,

Steve

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diff --git a/fs/cifs/CHANGES b/fs/cifs/CHANGES
index d43e0fe..b33c841 100644
--- a/fs/cifs/CHANGES
+++ b/fs/cifs/CHANGES
@@ -8,7 +8,9 @@ user's smb session.  This fix allows cifs to mount multiple times to the
 same server with different userids without risking invalidating earlier
 established security contexts.  fsync now sends SMB Flush operation
 to better ensure that we wait for server to write all of the data to
-server disk (not just write it over the network).
+server disk (not just write it over the network).  Add new mount
+parameter to allow user to disable sending the (slow) SMB flush on
+fsync if desired (fsync still flushes all cached write data to the server).
 
 Version 1.56
 ------------
diff --git a/fs/cifs/README b/fs/cifs/README
index da4515e..6436966 100644
--- a/fs/cifs/README
+++ b/fs/cifs/README
@@ -472,6 +472,19 @@ A partial list of the supported mount options follows:
 		even if the cifs server would support posix advisory locks.
 		"forcemand" is accepted as a shorter form of this mount
 		option.
+ nostrictsync   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.
  nodfs          Disable DFS (global name space support) even if the
 		server claims to support it.  This can help work around
 		a problem with parsing of DFS paths with Samba server
diff --git a/fs/cifs/cifs_fs_sb.h b/fs/cifs/cifs_fs_sb.h
index c4c306f..e9f177b 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 */
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index da0f4ff..18e84a4 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)
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 83b4741..6411f5f 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1538,7 +1538,8 @@ int cifs_fsync(struct file *file, struct dentry *dentry, int datasync)
 		rc = CIFS_I(inode)->write_behind_rc;
 		CIFS_I(inode)->write_behind_rc = 0;
 		tcon = CIFS_SB(inode->i_sb)->tcon;
-		if (!rc && tcon && smbfile)
+		if (!rc && tcon && smbfile &&
+		   !(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NO_SSYNC))
 			rc = CIFSSMBFlush(xid, tcon, smbfile->netfid);
 	}