xfs: reimplement fdatasync support

Add an in-memory only flag to say we logged timestamps only, and use it to
check if fdatasync can optimize away the log force.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_file.c

@@ -197,8 +197,11 @@ xfs_file_fsync(
 	 * to flush the log up to the latest LSN that touched the inode.
 	 */
 	xfs_ilock(ip, XFS_ILOCK_SHARED);
-	if (xfs_ipincount(ip))
-		lsn = ip->i_itemp->ili_last_lsn;
+	if (xfs_ipincount(ip)) {
+		if (!datasync ||
+		    (ip->i_itemp->ili_fields & ~XFS_ILOG_TIMESTAMP))
+			lsn = ip->i_itemp->ili_last_lsn;
+	}
 	xfs_iunlock(ip, XFS_ILOCK_SHARED);
 
 	if (lsn)

fs/xfs/xfs_inode_item.c

@@ -438,7 +438,8 @@ out:
 	 * games in recovery easier, which isn't a big deal as just about any
 	 * transaction would dirty it anyway.
 	 */
-	iip->ili_format.ilf_fields = XFS_ILOG_CORE | iip->ili_fields;
+	iip->ili_format.ilf_fields = XFS_ILOG_CORE |
+		(iip->ili_fields & ~XFS_ILOG_TIMESTAMP);
 	iip->ili_format.ilf_size = nvecs;
 }
 

fs/xfs/xfs_inode_item.h

@@ -86,6 +86,15 @@ typedef struct xfs_inode_log_format_64 {
 #define	XFS_ILOG_AEXT	0x080	/* log i_af.if_extents */
 #define	XFS_ILOG_ABROOT	0x100	/* log i_af.i_broot */
 
+
+/*
+ * The timestamps are dirty, but not necessarily anything else in the inode
+ * core.  Unlike the other fields above this one must never make it to disk
+ * in the ilf_fields of the inode_log_format, but is purely store in-memory in
+ * ili_fields in the inode_log_item.
+ */
+#define XFS_ILOG_TIMESTAMP	0x4000
+
 #define	XFS_ILOG_NONCORE	(XFS_ILOG_DDATA | XFS_ILOG_DEXT | \
 				 XFS_ILOG_DBROOT | XFS_ILOG_DEV | \
 				 XFS_ILOG_UUID | XFS_ILOG_ADATA | \
@@ -101,7 +110,7 @@ typedef struct xfs_inode_log_format_64 {
 				 XFS_ILOG_DEXT | XFS_ILOG_DBROOT | \
 				 XFS_ILOG_DEV | XFS_ILOG_UUID | \
 				 XFS_ILOG_ADATA | XFS_ILOG_AEXT | \
-				 XFS_ILOG_ABROOT)
+				 XFS_ILOG_ABROOT | XFS_ILOG_TIMESTAMP)
 
 static inline int xfs_ilog_fbroot(int w)
 {

fs/xfs/xfs_super.c

@@ -907,7 +907,7 @@ xfs_fs_dirty_inode(
 	ip->i_d.di_mtime.t_nsec = (__int32_t)inode->i_mtime.tv_nsec;
 
 	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
-	xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
+	xfs_trans_log_inode(tp, ip, XFS_ILOG_TIMESTAMP);
 	error = xfs_trans_commit(tp, 0);
 	if (error)
 		goto trouble;