xfs: Make fiemap work in query mode.

According to Documentation/filesystems/fiemap.txt, If fm_extent_count
is zero, then the fm_extents[] array is ignored (no extents will be
returned), and the fm_mapped_extents count will hold the number of
extents needed.

But as the commit 97db39a1f6f69e906e98118392400de5217aa33a has changed
bmv_count to the caller's input buffer, this number query function can't
work any more. As this commit is written to change bmv_count from
MAXEXTNUM because of ENOMEM.

This patch just try to  set bm.bmv_count to something sane.
Thanks to Dave Chinner <david@fromorbit.com> for the suggestion.

Cc: Eric Sandeen <sandeen@redhat.com>
Cc: Alex Elder <aelder@sgi.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tao Ma <tao.ma@oracle.com>

diff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c
index e65a793..9c8019c 100644 (file)
--- a/fs/xfs/linux-2.6/xfs_iops.c
+++ b/fs/xfs/linux-2.6/xfs_iops.c
@@ -673,7 +673,10 @@ xfs_vn_fiemap(
                bm.bmv_length = BTOBB(length);
 
        /* We add one because in getbmap world count includes the header */
-       bm.bmv_count = fieinfo->fi_extents_max + 1;
+       bm.bmv_count = !fieinfo->fi_extents_max ? MAXEXTNUM :
+                                       fieinfo->fi_extents_max + 1;
+       bm.bmv_count = min_t(__s32, bm.bmv_count,
+                            (PAGE_SIZE * 16 / sizeof(struct getbmapx)));
        bm.bmv_iflags = BMV_IF_PREALLOC;
        if (fieinfo->fi_flags & FIEMAP_FLAG_XATTR)
                bm.bmv_iflags |= BMV_IF_ATTRFORK;