xfs: make xfs_buf_get return an error code

Convert xfs_buf_get() to return numeric error codes like most
everywhere else in xfs.
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_attr_remote.c

@@ -545,9 +545,9 @@ xfs_attr_rmtval_set(
 		dblkno = XFS_FSB_TO_DADDR(mp, map.br_startblock),
 		dblkcnt = XFS_FSB_TO_BB(mp, map.br_blockcount);
 
-		bp = xfs_buf_get(mp->m_ddev_targp, dblkno, dblkcnt);
-		if (!bp)
-			return -ENOMEM;
+		error = xfs_buf_get(mp->m_ddev_targp, dblkno, dblkcnt, &bp);
+		if (error)
+			return error;
 		bp->b_ops = &xfs_attr3_rmt_buf_ops;
 
 		xfs_attr_rmtval_copyin(mp, bp, args->dp->i_ino, &offset,

fs/xfs/libxfs/xfs_sb.c

@@ -985,9 +985,9 @@ xfs_update_secondary_sbs(
 	for (agno = 1; agno < mp->m_sb.sb_agcount; agno++) {
 		struct xfs_buf		*bp;
 
-		bp = xfs_buf_get(mp->m_ddev_targp,
+		error = xfs_buf_get(mp->m_ddev_targp,
 				 XFS_AG_DADDR(mp, agno, XFS_SB_DADDR),
-				 XFS_FSS_TO_BB(mp, 1));
+				 XFS_FSS_TO_BB(mp, 1), &bp);
 		/*
 		 * If we get an error reading or writing alternate superblocks,
 		 * continue.  xfs_repair chooses the "best" superblock based
@@ -995,12 +995,12 @@ xfs_update_secondary_sbs(
 		 * superblocks un-updated than updated, and xfs_repair may
 		 * pick them over the properly-updated primary.
 		 */
-		if (!bp) {
+		if (error) {
 			xfs_warn(mp,
 		"error allocating secondary superblock for ag %d",
 				agno);
 			if (!saved_error)
-				saved_error = -ENOMEM;
+				saved_error = error;
 			continue;
 		}
 

fs/xfs/xfs_buf.h

@@ -201,20 +201,16 @@ void xfs_buf_readahead_map(struct xfs_buftarg *target,
 			       struct xfs_buf_map *map, int nmaps,
 			       const struct xfs_buf_ops *ops);
 
-static inline struct xfs_buf *
+static inline int
 xfs_buf_get(
 	struct xfs_buftarg	*target,
 	xfs_daddr_t		blkno,
-	size_t			numblks)
+	size_t			numblks,
+	struct xfs_buf		**bpp)
 {
-	struct xfs_buf		*bp;
-	int			error;
 	DEFINE_SINGLE_BUF_MAP(map, blkno, numblks);
 
-	error = xfs_buf_get_map(target, &map, 1, 0, &bp);
-	if (error)
-		return NULL;
-	return bp;
+	return xfs_buf_get_map(target, &map, 1, 0, bpp);
 }
 
 static inline struct xfs_buf *