xfs: uncached buffer reads need to return an error

With verification being done as an IO completion callback, different
errors can be returned from a read. Uncached reads only return a
buffer or NULL on failure, which means the verification error cannot
be returned to the caller.

Split the error handling for these reads into two - a failure to get
a buffer will still return NULL, but a read error will return a
referenced buffer with b_error set rather than NULL. The caller is
responsible for checking the error state of the buffer returned.

Signed-off-by: Dave Chinner <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Phil White <[e-mail]>
Signed-off-by: Ben Myers <[e-mail]>

fs/xfs/xfs_buf.c

···
 	int			flags,
 	xfs_buf_iodone_t	verify)
 {
-	xfs_buf_t		*bp;
-	int			error;
+	struct xfs_buf		*bp;
 
 	bp = xfs_buf_get_uncached(target, numblks, flags);
 	if (!bp)
···
 	bp->b_iodone = verify;
 
 	xfsbdstrat(target->bt_mount, bp);
-	error = xfs_buf_iowait(bp);
-	if (error) {
-		xfs_buf_relse(bp);
-		return NULL;
-	}
+	xfs_buf_iowait(bp);
 	return bp;
 }
 

fs/xfs/xfs_fsops.c

···
 				XFS_FSS_TO_BB(mp, 1), 0, NULL);
 	if (!bp)
 		return EIO;
+	if (bp->b_error) {
+		int	error = bp->b_error;
+		xfs_buf_relse(bp);
+		return error;
+	}
 	xfs_buf_relse(bp);
 
 	new = nb;	/* use new as a temporary here */

fs/xfs/xfs_mount.c

···
 			xfs_warn(mp, "SB buffer read failed");
 		return EIO;
 	}
+	if (bp->b_error) {
+		error = bp->b_error;
+		if (loud)
+			xfs_warn(mp, "SB validate failed");
+		goto release_buf;
+	}
 
 	/*
 	 * Initialize the mount structure from the superblock.

fs/xfs/xfs_rtalloc.c

···
 				XFS_FSB_TO_BB(mp, 1), 0, NULL);
 	if (!bp)
 		return EIO;
+	if (bp->b_error) {
+		error = bp->b_error;
+		xfs_buf_relse(bp);
+		return error;
+	}
 	xfs_buf_relse(bp);
 
 	/*
···
 	bp = xfs_buf_read_uncached(mp->m_rtdev_targp,
 					d - XFS_FSB_TO_BB(mp, 1),
 					XFS_FSB_TO_BB(mp, 1), 0, NULL);
-	if (!bp) {
+	if (!bp || bp->b_error) {
 		xfs_warn(mp, "realtime device size check failed");
+		if (bp)
+			xfs_buf_relse(bp);
 		return EIO;
 	}
 	xfs_buf_relse(bp);