xfs: make buffer read verication an IO completion function

Add a verifier function callback capability to the buffer read
interfaces.  This will be used by the callers to supply a function
that verifies the contents of the buffer when it is read from disk.
This patch does not provide callback functions, but simply modifies
the interfaces to allow them to be called.

The reason for adding this to the read interfaces is that it is very
difficult to tell fom the outside is a buffer was just read from
disk or whether we just pulled it out of cache. Supplying a callbck
allows the buffer cache to use it's internal knowledge of the buffer
to execute it only when the buffer is read from disk.

It is intended that the verifier functions will mark the buffer with
an EFSCORRUPTED error when verification fails. This allows the
reading context to distinguish a verification error from an IO
error, and potentially take further actions on the buffer (e.g.
attempt repair) based on the error reported.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Phil White <pwhite@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 8 insertions, 11 deletions

diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index db056544cbb5..f02d40296506 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -464,10 +464,7 @@ xfs_trans_get_buf(
         int                     numblks,
         uint                    flags)
 {
-        struct xfs_buf_map      map = {
-                .bm_bn = blkno,
-                .bm_len = numblks,
-        };
+        DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
         return xfs_trans_get_buf_map(tp, target, &map, 1, flags);
 }
 
@@ -476,7 +473,8 @@ int		xfs_trans_read_buf_map(struct xfs_mount *mp,
                                        struct xfs_buftarg *target,
                                        struct xfs_buf_map *map, int nmaps,
                                        xfs_buf_flags_t flags,
-                                       struct xfs_buf **bpp);
+                                       struct xfs_buf **bpp,
+                                       xfs_buf_iodone_t verify);
 
 static inline int
 xfs_trans_read_buf(
@@ -486,13 +484,12 @@ xfs_trans_read_buf(
         xfs_daddr_t             blkno,
         int                     numblks,
         xfs_buf_flags_t         flags,
-        struct xfs_buf          **bpp)
+        struct xfs_buf          **bpp,
+        xfs_buf_iodone_t        verify)
 {
-        struct xfs_buf_map      map = {
-                .bm_bn = blkno,
-                .bm_len = numblks,
-        };
-        return xfs_trans_read_buf_map(mp, tp, target, &map, 1, flags, bpp);
+        DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
+        return xfs_trans_read_buf_map(mp, tp, target, &map, 1,
+                                      flags, bpp, verify);
 }
 
 struct xfs_buf  *xfs_trans_getsb(xfs_trans_t *, struct xfs_mount *, int);