xfs: don't rely on extent indices in xfs_bmap_collapse_extents

Rewrite xfs_bmap_collapse_extents so that we don't rely on extent indices
except for iterating over them.  Not being able to iterate to the next
extent is a sufficient exit condition, and we don't need to do any extent
count games given that:

  a) we already flushed all delalloc extents past our start offset
     before doing the operation
  b) xfs_iext_count() includes delalloc extents anyway

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 680be05..cdec39b 100644 (file)
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -5637,8 +5637,6 @@ xfs_bmap_collapse_extents(
        struct xfs_btree_cur    *cur = NULL;
        struct xfs_bmbt_irec    got, prev;
        xfs_extnum_t            current_ext;
-       xfs_extnum_t            total_extents;
-       xfs_extnum_t            stop_extent;
        xfs_fileoff_t           new_startoff;
        int                     error = 0;
        int                     logflags = 0;
@@ -5669,52 +5667,31 @@ xfs_bmap_collapse_extents(
                cur->bc_private.b.flags = 0;
        }
 
-       /*
-        * There may be delalloc extents in the data fork before the range we
-        * are collapsing out, so we cannot use the count of real extents here.
-        * Instead we have to calculate it from the incore fork.
-        */
-       total_extents = xfs_iext_count(ifp);
-       if (total_extents == 0) {
-               *done = true;
-               goto del_cursor;
-       }
-
-       /*
-        * Look up the extent index for the fsb where we start shifting. We can
-        * henceforth iterate with current_ext as extent list changes are locked
-        * out via ilock.
-        *
-        * If next_fsb lies in a hole beyond which there are no extents we are
-        * done.
-        */
        if (!xfs_iext_lookup_extent(ip, ifp, *next_fsb, &current_ext, &got)) {
                *done = true;
                goto del_cursor;
        }
        XFS_WANT_CORRUPTED_RETURN(mp, !isnullstartblock(got.br_startblock));
 
-       stop_extent = total_extents;
-       if (current_ext >= stop_extent) {
-               error = -EIO;
-               goto del_cursor;
-       }
-
        new_startoff = got.br_startoff - offset_shift_fsb;
-       if (current_ext) {
-               xfs_iext_get_extent(ifp, current_ext - 1, &prev);
+       if (xfs_iext_get_extent(ifp, current_ext - 1, &prev)) {
                if (new_startoff < prev.br_startoff + prev.br_blockcount) {
                        error = -EINVAL;
                        goto del_cursor;
                }
 
-               /* check whether to merge the extent or shift it down */
                if (xfs_bmse_can_merge(&prev, &got, offset_shift_fsb)) {
                        error = xfs_bmse_merge(ip, whichfork, offset_shift_fsb,
                                        current_ext, &got, &prev, cur,
                                        &logflags, dfops);
                        if (error)
                                goto del_cursor;
+
+                       /* update got after merge */
+                       if (!xfs_iext_get_extent(ifp, current_ext, &got)) {
+                               *done = true;
+                               goto del_cursor;
+                       }
                        goto done;
                }
        } else {
@@ -5728,20 +5705,13 @@ xfs_bmap_collapse_extents(
                        cur, &logflags, dfops, new_startoff);
        if (error)
                goto del_cursor;
-       current_ext++;
-done:
-       /*
-        * If there was an extent merge during the shift, the extent
-        * count can change. Update the total and grade the next record.
-        */
-       total_extents = xfs_iext_count(ifp);
-       stop_extent = total_extents;
-       if (current_ext == stop_extent) {
-               *done = true;
-               goto del_cursor;
+
+       if (!xfs_iext_get_extent(ifp, ++current_ext, &got)) {
+                *done = true;
+                goto del_cursor;
        }
-       xfs_iext_get_extent(ifp, current_ext, &got);
 
+done:
        *next_fsb = got.br_startoff;
 del_cursor:
        if (cur)