xfs
[Top] [All Lists]

[PATCH v6 4/4] xfs: xfs_seek_hole() refinement with lookup hole offset

To: xfs@xxxxxxxxxxx
Subject: [PATCH v6 4/4] xfs: xfs_seek_hole() refinement with lookup hole offset from page cache
From: Jeff Liu <jeff.liu@xxxxxxxxxx>
Date: Fri, 03 Aug 2012 14:11:14 +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
xfs_seek_hole() refinement with hole searching from page cache for unwritten 
extent.


Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>

---
 fs/xfs/xfs_file.c |   79 ++++++++++++++++++++++++++++++++++++++++++++++-------
 1 files changed, 69 insertions(+), 10 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index e852e52..0ab27eb 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1295,9 +1295,9 @@ 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;
 
@@ -1313,21 +1313,80 @@ 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;
+
+               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;
+               }
 
-       holeoff = XFS_FSB_TO_B(mp, fsbno);
-       if (holeoff <= start)
                offset = start;
-       else {
+               /* Landed in a hole */
+               if (map[0].br_startblock == HOLESTARTBLOCK)
+                       break;
+
                /*
-                * xfs_bmap_first_unused() could return a value bigger than
-                * isize if there are no more holes past the supplied offset.
+                * Landed in an unwritten extent, try to search hole from
+                * page cache.
                 */
-               offset = min_t(loff_t, holeoff, isize);
+               if (map[0].br_state == XFS_EXT_UNWRITTEN) {
+                       if (xfs_find_get_desired_pgoff(inode, &map[0],
+                                                      HOLE_OFF, &offset))
+                               break;
+               }
+
+               /*
+                * 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;
+               }
+
+               /* We have two mappings, proceed to check map[1] */
+               offset = XFS_FSB_TO_B(mp, map[1].br_startoff);
+               if (map[1].br_startblock == HOLESTARTBLOCK)
+                       break;
+
+               if (map[1].br_state == XFS_EXT_UNWRITTEN) {
+                       if (xfs_find_get_desired_pgoff(inode, &map[1],
+                                                      HOLE_OFF, &offset))
+                               break;
+               }
+
+               /*
+                * Both mappings contains data, proceed to the next round of
+                * search if the current reading offset not beyond or hit EOF.
+                */
+               fsbno = map[1].br_startoff + map[1].br_blockcount;
+               start = XFS_FSB_TO_B(mp, fsbno);
+               if (start >= isize) {
+                       offset = isize;
+                       break;
+               }
        }
 
+       /*
+        * 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

<Prev in Thread] Current Thread [Next in Thread>