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

[Steve French]

On Fri, Feb 20, 2009 at 2:51 PM, Horst Reiterer
<horst.reiterer@xxxxxxxxx> wrote:
> Hi,
>
> In contrast to the now-obsolete smbfs, cifs does not send SMB_COM_FLUSH
> in response to an explicit fsync(2) to guarantee that all volatile data
> is written to stable storage on the server side, provided the server
> honors the request (which, to my knowledge, is true for Windows and
> Samba with 'strict sync' enabled).
> This patch modifies the cifs_fsync implementation

I modified your patch slightly to not lose the writeback rc in one
case, and to change camel case pTcon to tcon and remove one
unnecessary local variable.

See attached.   Thanks for the submission - looks fine otherwise.   If
you have any performance numbers before and after (with e.g. dbench,
iozone, bonnie etc. or perhaps something which calls fsync more often
- that would be helpful in determining whether we need a mount option
to optionally disable it - as the samba server does)


-- 
Thanks,

Steve
diff --git a/fs/cifs/CHANGES b/fs/cifs/CHANGES
index 851388f..d43e0fe 100644
--- a/fs/cifs/CHANGES
+++ b/fs/cifs/CHANGES
@@ -6,7 +6,9 @@ the server to treat subsequent connections, especially those that
 are authenticated as guest, as reconnections, invalidating the earlier
 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.
+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).
 
 Version 1.56
 ------------
diff --git a/fs/cifs/cifs_debug.c b/fs/cifs/cifs_debug.c
index 490e34b..877e4d9 100644
--- a/fs/cifs/cifs_debug.c
+++ b/fs/cifs/cifs_debug.c
@@ -340,6 +340,8 @@ static int cifs_stats_proc_show(struct seq_file *m, void *v)
 				seq_printf(m, "\nWrites: %d Bytes: %lld",
 					atomic_read(&tcon->num_writes),
 					(long long)(tcon->bytes_written));
+				seq_printf(m, "\nFlushes: %d",
+					atomic_read(&tcon->num_flushes));
 				seq_printf(m, "\nLocks: %d HardLinks: %d "
 					      "Symlinks: %d",
 					atomic_read(&tcon->num_locks),
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index e004f6d..44ff94d 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -254,6 +254,7 @@ struct cifsTconInfo {
 	atomic_t num_smbs_sent;
 	atomic_t num_writes;
 	atomic_t num_reads;
+	atomic_t num_flushes;
 	atomic_t num_oplock_brks;
 	atomic_t num_opens;
 	atomic_t num_closes;
diff --git a/fs/cifs/cifspdu.h b/fs/cifs/cifspdu.h
index b4e2e9f..eda6e51 100644
--- a/fs/cifs/cifspdu.h
+++ b/fs/cifs/cifspdu.h
@@ -43,6 +43,7 @@
 #define SMB_COM_CREATE_DIRECTORY      0x00 /* trivial response */
 #define SMB_COM_DELETE_DIRECTORY      0x01 /* trivial response */
 #define SMB_COM_CLOSE                 0x04 /* triv req/rsp, timestamp ignored */
+#define SMB_COM_FLUSH                 0x05 /* triv req/rsp */
 #define SMB_COM_DELETE                0x06 /* trivial response */
 #define SMB_COM_RENAME                0x07 /* trivial response */
 #define SMB_COM_QUERY_INFORMATION     0x08 /* aka getattr */
@@ -790,6 +791,12 @@ typedef struct smb_com_close_rsp {
 	__u16 ByteCount;	/* bct = 0 */
 } __attribute__((packed)) CLOSE_RSP;
 
+typedef struct smb_com_flush_req {
+	struct smb_hdr hdr;	/* wct = 1 */
+	__u16 FileID;
+	__u16 ByteCount;	/* 0 */
+} __attribute__((packed)) FLUSH_REQ;
+
 typedef struct smb_com_findclose_req {
 	struct smb_hdr hdr; /* wct = 1 */
 	__u16 FileID;
diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h
index 083dfc5..596fc86 100644
--- a/fs/cifs/cifsproto.h
+++ b/fs/cifs/cifsproto.h
@@ -281,6 +281,9 @@ extern int CIFSPOSIXCreate(const int xid, struct cifsTconInfo *tcon,
 extern int CIFSSMBClose(const int xid, struct cifsTconInfo *tcon,
 			const int smb_file_id);
 
+extern int CIFSSMBFlush(const int xid, struct cifsTconInfo *tcon,
+			const int smb_file_id);
+
 extern int CIFSSMBRead(const int xid, struct cifsTconInfo *tcon,
 			const int netfid, unsigned int count,
 			const __u64 lseek, unsigned int *nbytes, char **buf,
diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index 939e2f7..4c344fe 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -1934,6 +1934,27 @@ CIFSSMBClose(const int xid, struct cifsTconInfo *tcon, int smb_file_id)
 }
 
 int
+CIFSSMBFlush(const int xid, struct cifsTconInfo *tcon, int smb_file_id)
+{
+	int rc = 0;
+	FLUSH_REQ *pSMB = NULL;
+	cFYI(1, ("In CIFSSMBFlush"));
+
+	rc = small_smb_init(SMB_COM_FLUSH, 1, tcon, (void **) &pSMB);
+	if (rc)
+		return rc;
+
+	pSMB->FileID = (__u16) smb_file_id;
+	pSMB->ByteCount = 0;
+	rc = SendReceiveNoRsp(xid, tcon->ses, (struct smb_hdr *) pSMB, 0);
+	cifs_stats_inc(&tcon->num_flushes);
+	if (rc)
+		cERROR(1, ("Send error in Flush = %d", rc));
+
+	return rc;
+}
+
+int
 CIFSSMBRename(const int xid, struct cifsTconInfo *tcon,
 	      const char *fromName, const char *toName,
 	      const struct nls_table *nls_codepage, int remap)
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 12bb656..83b4741 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1523,6 +1523,9 @@ int cifs_fsync(struct file *file, struct dentry *dentry, int datasync)
 {
 	int xid;
 	int rc = 0;
+	struct cifsTconInfo *tcon;
+	struct cifsFileInfo *smbfile =
+		(struct cifsFileInfo *)file->private_data;
 	struct inode *inode = file->f_path.dentry->d_inode;
 
 	xid = GetXid();
@@ -1534,7 +1537,11 @@ int cifs_fsync(struct file *file, struct dentry *dentry, int datasync)
 	if (rc == 0) {
 		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)
+			rc = CIFSSMBFlush(xid, tcon, smbfile->netfid);
 	}
+
 	FreeXid(xid);
 	return rc;
 }