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, 9 insertions, 4 deletions

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 4b0b8dd1b7b0..0298dd684798 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -654,7 +654,8 @@ xfs_buf_read_map(
 	struct xfs_buftarg	*target,
 	struct xfs_buf_map	*map,
 	int			nmaps,
-	xfs_buf_flags_t		flags)
+	xfs_buf_flags_t		flags,
+	xfs_buf_iodone_t	verify)
 {
 	struct xfs_buf		*bp;
 
@@ -666,6 +667,7 @@ xfs_buf_read_map(
 
 		if (!XFS_BUF_ISDONE(bp)) {
 			XFS_STATS_INC(xb_get_read);
+			bp->b_iodone = verify;
 			_xfs_buf_read(bp, flags);
 		} else if (flags & XBF_ASYNC) {
 			/*
@@ -691,13 +693,14 @@ void
 xfs_buf_readahead_map(
 	struct xfs_buftarg	*target,
 	struct xfs_buf_map	*map,
-	int			nmaps)
+	int			nmaps,
+	xfs_buf_iodone_t	verify)
 {
 	if (bdi_read_congested(target->bt_bdi))
 		return;
 
 	xfs_buf_read_map(target, map, nmaps,
-		     XBF_TRYLOCK|XBF_ASYNC|XBF_READ_AHEAD);
+		     XBF_TRYLOCK|XBF_ASYNC|XBF_READ_AHEAD, verify);
 }
 
 /*
@@ -709,7 +712,8 @@ xfs_buf_read_uncached(
 	struct xfs_buftarg	*target,
 	xfs_daddr_t		daddr,
 	size_t			numblks,
-	int			flags)
+	int			flags,
+	xfs_buf_iodone_t	verify)
 {
 	xfs_buf_t		*bp;
 	int			error;
@@ -723,6 +727,7 @@ xfs_buf_read_uncached(
 	bp->b_bn = daddr;
 	bp->b_maps[0].bm_bn = daddr;
 	bp->b_flags |= XBF_READ;
+	bp->b_iodone = verify;
 
 	xfsbdstrat(target->bt_mount, bp);
 	error = xfs_buf_iowait(bp);