[PATCH 8/8] xfs: reimplement fdatasync support

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

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@xxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>

---
 fs/xfs/xfs_file.c       |    7 +++++--
 fs/xfs/xfs_inode_item.c |    3 ++-
 fs/xfs/xfs_inode_item.h |   11 ++++++++++-
 fs/xfs/xfs_super.c      |    2 +-
 4 files changed, 18 insertions(+), 5 deletions(-)

Index: xfs/fs/xfs/xfs_inode_item.c
===================================================================
--- xfs.orig/fs/xfs/xfs_inode_item.c    2012-02-28 12:02:29.643918816 +0100
+++ xfs/fs/xfs/xfs_inode_item.c 2012-02-28 12:02:53.871918171 +0100
@@ -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;
 }
 
Index: xfs/fs/xfs/xfs_inode_item.h
===================================================================
--- xfs.orig/fs/xfs/xfs_inode_item.h    2012-02-28 12:02:29.643918816 +0100
+++ xfs/fs/xfs/xfs_inode_item.h 2012-02-28 12:04:47.539915134 +0100
@@ -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)
 {
Index: xfs/fs/xfs/xfs_file.c
===================================================================
--- xfs.orig/fs/xfs/xfs_file.c  2012-02-28 12:01:00.063921211 +0100
+++ xfs/fs/xfs/xfs_file.c       2012-02-28 12:02:53.875918171 +0100
@@ -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)
Index: xfs/fs/xfs/xfs_super.c
===================================================================
--- xfs.orig/fs/xfs/xfs_super.c 2012-02-28 12:01:00.071921207 +0100
+++ xfs/fs/xfs/xfs_super.c      2012-02-28 12:02:53.875918171 +0100
@@ -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;