xfs: xfs_seek_hole() refinement with hole searching from page cache for unwritten extents

xfs_seek_hole() refinement with hole searching from page cache for unwritten extent.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 67 insertions, 11 deletions

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 3f9107431dfb..1eaeb8be3aae 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1289,9 +1289,9 @@ 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;
 
@@ -1307,21 +1307,77 @@ 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;
+                        }
+                }
 
-        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.
+                 * 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).
                  */
-                offset = min_t(loff_t, holeoff, isize);
+                if (nmap == 1) {
+                        offset = isize;
+                        break;
+                }
+
+                ASSERT(i > 1);
+
+                /*
+                 * Both mappings contains data, proceed to the next round of
+                 * search if the current reading offset not beyond or hit EOF.
+                 */
+                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;