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[PATCH v7 4/4] xfs: xfs_seek_hole() refinement with hole searching from

To: xfs@xxxxxxxxxxx
Subject: [PATCH v7 4/4] xfs: xfs_seek_hole() refinement with hole searching from page cache for unwritten extent
From: Jeff Liu <jeff.liu@xxxxxxxxxx>
Date: Mon, 13 Aug 2012 21:08:13 +0800
Organization: Oracle
Reply-to: jeff.liu@xxxxxxxxxx
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.28) Gecko/20120313 Thunderbird/3.1.20
Improve xfs_seek_hole() to search hole offset from page cache for unwritten 
extents.

Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
---
 fs/xfs/xfs_file.c |   76 +++++++++++++++++++++++++++++++++++++++++++++-------
 1 files changed, 65 insertions(+), 11 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 43b3718..a537f61 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1288,9 +1288,9 @@ xfs_seek_hole(
        struct xfs_inode        *ip = XFS_I(inode);
        struct xfs_mount        *mp = ip->i_mount;
        loff_t                  uninitialized_var(offset);
-       loff_t                  holeoff;
        xfs_fsize_t             isize;
        xfs_fileoff_t           fsbno;
+       xfs_filblks_t           end;
        uint                    lock;
        int                     error;
 
@@ -1306,21 +1306,75 @@ xfs_seek_hole(
        }
 
        fsbno = XFS_B_TO_FSBT(mp, start);
-       error = xfs_bmap_first_unused(NULL, ip, 1, &fsbno, XFS_DATA_FORK);
-       if (error)
-               goto out_unlock;
+       end = XFS_B_TO_FSB(mp, isize);
+
+       for (;;) {
+               struct xfs_bmbt_irec    map[2];
+               int                     nmap = 2;
+               unsigned int            i;
+
+               error = xfs_bmapi_read(ip, fsbno, end - fsbno, map, &nmap,
+                                      XFS_BMAPI_ENTIRE);
+               if (error)
+                       goto out_unlock;
+
+               /* No extents at given offset, must be beyond EOF */
+               if (nmap == 0) {
+                       error = ENXIO;
+                       goto out_unlock;
+               }
+
+               for (i = 0; i < nmap; i++) {
+                       offset = max_t(loff_t, start,
+                                      XFS_FSB_TO_B(mp, map[i].br_startoff));
+
+                       /* Landed in a hole */
+                       if (map[i].br_startblock == HOLESTARTBLOCK)
+                               goto out;
+
+                       /*
+                        * Landed in an unwritten extent, try to search hole
+                        * from page cache.
+                        */
+                       if (map[i].br_state == XFS_EXT_UNWRITTEN) {
+                               if (xfs_find_get_desired_pgoff(inode, &map[i],
+                                                       HOLE_OFF, &offset))
+                                       goto out;
+                       }
+               }
+
+               /*
+                * map[0] contains data or its unwritten but contains
+                * data in page cache, probably means that we are
+                * reading after EOF.  We should fix offset to point
+                * to the end of the file(i.e., there is an implicit
+                * hole at the end of any file).
+                */
+               if (nmap == 1) {
+                       offset = isize;
+                       break;
+               }
 
-       holeoff = XFS_FSB_TO_B(mp, fsbno);
-       if (holeoff <= start)
-               offset = start;
-       else {
                /*
-                * xfs_bmap_first_unused() could return a value bigger than
-                * isize if there are no more holes past the supplied offset.
+                * Both mappings contains data, proceed to the next round of
+                * search if the current reading offset not beyond or hit EOF.
                 */
-               offset = min_t(loff_t, holeoff, isize);
+               fsbno = map[i - 1].br_startoff + map[i - 1].br_blockcount;
+               start = XFS_FSB_TO_B(mp, fsbno);
+               if (start >= isize) {
+                       offset = isize;
+                       break;
+               }
        }
 
+out:
+       /*
+        * At this point, we must have found a hole.  However, the returned
+        * offset may be bigger than the file size as it may be aligned to
+        * page boundary for unwritten extents, we need to deal with this
+        * situation in particular.
+        */
+       offset = min_t(loff_t, offset, isize);
        if (offset != file->f_pos)
                file->f_pos = offset;
 
-- 
1.7.4.1

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