xfs: make xfs_buf_read_map return an error code

Convert xfs_buf_read_map() to return numeric error codes like most
everywhere else in xfs.  This involves moving the open-coded logic that
reports metadata IO read / corruption errors and stales the buffer into
xfs_buf_read_map so that the logic is all in one place.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/libxfs/xfs_alloc.c

@@ -2956,14 +2956,17 @@ xfs_read_agf(
 	trace_xfs_read_agf(mp, agno);
 
 	ASSERT(agno != NULLAGNUMBER);
-	error = xfs_trans_read_buf(
-			mp, tp, mp->m_ddev_targp,
+	error = xfs_trans_read_buf(mp, tp, mp->m_ddev_targp,
 			XFS_AG_DADDR(mp, agno, XFS_AGF_DADDR(mp)),
 			XFS_FSS_TO_BB(mp, 1), flags, bpp, &xfs_agf_buf_ops);
+	/*
+	 * Callers of xfs_read_agf() currently interpret a NULL bpp as EAGAIN
+	 * and need to be converted to check for EAGAIN specifically.
+	 */
+	if (error == -EAGAIN)
+		return 0;
 	if (error)
 		return error;
-	if (!*bpp)
-		return 0;
 
 	ASSERT(!(*bpp)->b_error);
 	xfs_buf_set_ref(*bpp, XFS_AGF_REF);

fs/xfs/libxfs/xfs_attr_remote.c

@@ -422,16 +422,6 @@ xfs_attr_rmtval_get(
 					&xfs_attr3_rmt_buf_ops);
 			if (!bp)
 				return -ENOMEM;
-			error = bp->b_error;
-			if (error) {
-				xfs_buf_ioerror_alert(bp, __func__);
-				xfs_buf_relse(bp);
-
-				/* bad CRC means corrupted metadata */
-				if (error == -EFSBADCRC)
-					error = -EFSCORRUPTED;
-				return error;
-			}
 
 			error = xfs_attr_rmtval_copyout(mp, bp, args->dp->i_ino,
 							&offset, &valuelen,

fs/xfs/xfs_buf.c

@@ -796,47 +796,76 @@ xfs_buf_reverify(
 	return bp->b_error;
 }
 
-xfs_buf_t *
+int
 xfs_buf_read_map(
 	struct xfs_buftarg	*target,
 	struct xfs_buf_map	*map,
 	int			nmaps,
 	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp,
 	const struct xfs_buf_ops *ops)
 {
 	struct xfs_buf		*bp;
 	int			error;
 
 	flags |= XBF_READ;
+	*bpp = NULL;
 
 	error = xfs_buf_get_map(target, map, nmaps, flags, &bp);
 	if (error)
-		return NULL;
+		return error;
 
 	trace_xfs_buf_read(bp, flags, _RET_IP_);
 
 	if (!(bp->b_flags & XBF_DONE)) {
+		/* Initiate the buffer read and wait. */
 		XFS_STATS_INC(target->bt_mount, xb_get_read);
 		bp->b_ops = ops;
-		_xfs_buf_read(bp, flags);
-		return bp;
-	}
+		error = _xfs_buf_read(bp, flags);
 
-	xfs_buf_reverify(bp, ops);
+		/* Readahead iodone already dropped the buffer, so exit. */
+		if (flags & XBF_ASYNC)
+			return 0;
+	} else {
+		/* Buffer already read; all we need to do is check it. */
+		error = xfs_buf_reverify(bp, ops);
 
+		/* Readahead already finished; drop the buffer and exit. */
 		if (flags & XBF_ASYNC) {
-		/*
-		 * Read ahead call which is already satisfied,
-		 * drop the buffer
-		 */
 			xfs_buf_relse(bp);
-		return NULL;
+			return 0;
 		}
 
 		/* We do not want read in the flags */
 		bp->b_flags &= ~XBF_READ;
 		ASSERT(bp->b_ops != NULL || ops == NULL);
-	return bp;
+	}
+
+	/*
+	 * If we've had a read error, then the contents of the buffer are
+	 * invalid and should not be used. To ensure that a followup read tries
+	 * to pull the buffer from disk again, we clear the XBF_DONE flag and
+	 * mark the buffer stale. This ensures that anyone who has a current
+	 * reference to the buffer will interpret it's contents correctly and
+	 * future cache lookups will also treat it as an empty, uninitialised
+	 * buffer.
+	 */
+	if (error) {
+		if (!XFS_FORCED_SHUTDOWN(target->bt_mount))
+			xfs_buf_ioerror_alert(bp, __func__);
+
+		bp->b_flags &= ~XBF_DONE;
+		xfs_buf_stale(bp);
+		xfs_buf_relse(bp);
+
+		/* bad CRC means corrupted metadata */
+		if (error == -EFSBADCRC)
+			error = -EFSCORRUPTED;
+		return error;
+	}
+
+	*bpp = bp;
+	return 0;
 }
 
 /*
@@ -850,11 +879,13 @@ xfs_buf_readahead_map(
 	int			nmaps,
 	const struct xfs_buf_ops *ops)
 {
+	struct xfs_buf		*bp;
+
 	if (bdi_read_congested(target->bt_bdev->bd_bdi))
 		return;
 
 	xfs_buf_read_map(target, map, nmaps,
-		     XBF_TRYLOCK|XBF_ASYNC|XBF_READ_AHEAD, ops);
+		     XBF_TRYLOCK | XBF_ASYNC | XBF_READ_AHEAD, &bp, ops);
 }
 
 /*

fs/xfs/xfs_buf.h

@@ -194,9 +194,8 @@ struct xfs_buf *xfs_buf_incore(struct xfs_buftarg *target,
 
 int xfs_buf_get_map(struct xfs_buftarg *target, struct xfs_buf_map *map,
 		int nmaps, xfs_buf_flags_t flags, struct xfs_buf **bpp);
-struct xfs_buf *xfs_buf_read_map(struct xfs_buftarg *target,
-			       struct xfs_buf_map *map, int nmaps,
-			       xfs_buf_flags_t flags,
+int xfs_buf_read_map(struct xfs_buftarg *target, struct xfs_buf_map *map,
+		int nmaps, xfs_buf_flags_t flags, struct xfs_buf **bpp,
 		const struct xfs_buf_ops *ops);
 void xfs_buf_readahead_map(struct xfs_buftarg *target,
 			       struct xfs_buf_map *map, int nmaps,
@@ -226,8 +225,14 @@ xfs_buf_read(
 	xfs_buf_flags_t		flags,
 	const struct xfs_buf_ops *ops)
 {
+	struct xfs_buf		*bp;
+	int			error;
 	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
-	return xfs_buf_read_map(target, &map, 1, flags, ops);
+
+	error = xfs_buf_read_map(target, &map, 1, flags, &bp, ops);
+	if (error)
+		return NULL;
+	return bp;
 }
 
 static inline void

fs/xfs/xfs_log_recover.c

@@ -2749,11 +2749,6 @@ xlog_recover_buffer_pass2(
 			  buf_flags, NULL);
 	if (!bp)
 		return -ENOMEM;
-	error = bp->b_error;
-	if (error) {
-		xfs_buf_ioerror_alert(bp, "xlog_recover_do..(read#1)");
-		goto out_release;
-	}
 
 	/*
 	 * Recover the buffer only if we get an LSN from it and it's less than
@@ -2956,11 +2951,6 @@ xlog_recover_inode_pass2(
 		error = -ENOMEM;
 		goto error;
 	}
-	error = bp->b_error;
-	if (error) {
-		xfs_buf_ioerror_alert(bp, "xlog_recover_do..(read#2)");
-		goto out_release;
-	}
 	ASSERT(in_f->ilf_fields & XFS_ILOG_CORE);
 	dip = xfs_buf_offset(bp, in_f->ilf_boffset);
 

fs/xfs/xfs_symlink.c

@@ -57,16 +57,6 @@ xfs_readlink_bmap_ilocked(
 				  &xfs_symlink_buf_ops);
 		if (!bp)
 			return -ENOMEM;
-		error = bp->b_error;
-		if (error) {
-			xfs_buf_ioerror_alert(bp, __func__);
-			xfs_buf_relse(bp);
-
-			/* bad CRC means corrupted metadata */
-			if (error == -EFSBADCRC)
-				error = -EFSCORRUPTED;
-			goto out;
-		}
 		byte_cnt = XFS_SYMLINK_BUF_SPACE(mp, byte_cnt);
 		if (pathlen < byte_cnt)
 			byte_cnt = pathlen;

fs/xfs/xfs_trans_buf.c

@@ -302,36 +302,16 @@ xfs_trans_read_buf_map(
 		return 0;
 	}
 
-	bp = xfs_buf_read_map(target, map, nmaps, flags, ops);
-	if (!bp) {
-		if (!(flags & XBF_TRYLOCK))
-			return -ENOMEM;
-		return tp ? 0 : -EAGAIN;
-	}
-
-	/*
-	 * If we've had a read error, then the contents of the buffer are
-	 * invalid and should not be used. To ensure that a followup read tries
-	 * to pull the buffer from disk again, we clear the XBF_DONE flag and
-	 * mark the buffer stale. This ensures that anyone who has a current
-	 * reference to the buffer will interpret it's contents correctly and
-	 * future cache lookups will also treat it as an empty, uninitialised
-	 * buffer.
-	 */
-	if (bp->b_error) {
-		error = bp->b_error;
-		if (!XFS_FORCED_SHUTDOWN(mp))
-			xfs_buf_ioerror_alert(bp, __func__);
-		bp->b_flags &= ~XBF_DONE;
-		xfs_buf_stale(bp);
-
+	error = xfs_buf_read_map(target, map, nmaps, flags, &bp, ops);
+	switch (error) {
+	case 0:
+		break;
+	default:
 		if (tp && (tp->t_flags & XFS_TRANS_DIRTY))
 			xfs_force_shutdown(tp->t_mountp, SHUTDOWN_META_IO_ERROR);
-		xfs_buf_relse(bp);
-
-		/* bad CRC means corrupted metadata */
-		if (error == -EFSBADCRC)
-			error = -EFSCORRUPTED;
+		/* fall through */
+	case -ENOMEM:
+	case -EAGAIN:
 		return error;
 	}