xfs: handle nimaps=0 from xfs_bmapi_write in xfs_alloc_file_space

If xfs_bmapi_write finds a delalloc extent at the requested range, it
tries to convert the entire delalloc extent to a real allocation.

But if the allocator cannot find a single free extent large enough to
cover the start block of the requested range, xfs_bmapi_write will
return 0 but leave *nimaps set to 0.

In that case we simply need to keep looping with the same startoffset_fsb
so that one of the following allocations will eventually reach the
requested range.

Note that this could affect any caller of xfs_bmapi_write that covers
an existing delayed allocation.  As far as I can tell we do not have
any other such caller, though - the regular writeback path uses
xfs_bmapi_convert_delalloc to convert delayed allocations to real ones,
and direct I/O invalidates the page cache first.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index c640dfc2d00f61747b50bd82c416518000ef6f91..93829d86751dad6625091663000b43fb8981bcd6 100644 (file)
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -774,12 +774,10 @@ xfs_alloc_file_space(
 {
        xfs_mount_t             *mp = ip->i_mount;
        xfs_off_t               count;
-       xfs_filblks_t           allocated_fsb;
        xfs_filblks_t           allocatesize_fsb;
        xfs_extlen_t            extsz, temp;
        xfs_fileoff_t           startoffset_fsb;
        xfs_fileoff_t           endoffset_fsb;
-       int                     nimaps;
        int                     rt;
        xfs_trans_t             *tp;
        xfs_bmbt_irec_t         imaps[1], *imapp;
@@ -802,7 +800,6 @@ xfs_alloc_file_space(
 
        count = len;
        imapp = &imaps[0];
-       nimaps = 1;
        startoffset_fsb = XFS_B_TO_FSBT(mp, offset);
        endoffset_fsb = XFS_B_TO_FSB(mp, offset + count);
        allocatesize_fsb = endoffset_fsb - startoffset_fsb;
@@ -813,6 +810,7 @@ xfs_alloc_file_space(
        while (allocatesize_fsb && !error) {
                xfs_fileoff_t   s, e;
                unsigned int    dblocks, rblocks, resblks;
+               int             nimaps = 1;
 
                /*
                 * Determine space reservations for data/realtime.
@@ -878,15 +876,19 @@ xfs_alloc_file_space(
                if (error)
                        break;
 
-               allocated_fsb = imapp->br_blockcount;
-
-               if (nimaps == 0) {
-                       error = -ENOSPC;
-                       break;
+               /*
+                * If the allocator cannot find a single free extent large
+                * enough to cover the start block of the requested range,
+                * xfs_bmapi_write will return 0 but leave *nimaps set to 0.
+                *
+                * In that case we simply need to keep looping with the same
+                * startoffset_fsb so that one of the following allocations
+                * will eventually reach the requested range.
+                */
+               if (nimaps) {
+                       startoffset_fsb += imapp->br_blockcount;
+                       allocatesize_fsb -= imapp->br_blockcount;
                }
-
-               startoffset_fsb += allocated_fsb;
-               allocatesize_fsb -= allocated_fsb;
        }
 
        return error;