xfs: make xfs_buf_alloc return an error code

Convert _xfs_buf_alloc() 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/xfs_buf.c

@@ -198,20 +198,22 @@ xfs_buf_free_maps(
 	}
 }
 
-static struct xfs_buf *
+static int
 _xfs_buf_alloc(
 	struct xfs_buftarg	*target,
 	struct xfs_buf_map	*map,
 	int			nmaps,
-	xfs_buf_flags_t		flags)
+	xfs_buf_flags_t		flags,
+	struct xfs_buf		**bpp)
 {
 	struct xfs_buf		*bp;
 	int			error;
 	int			i;
 
+	*bpp = NULL;
 	bp = kmem_zone_zalloc(xfs_buf_zone, KM_NOFS);
 	if (unlikely(!bp))
-		return NULL;
+		return -ENOMEM;
 
 	/*
 	 * We don't want certain flags to appear in b_flags unless they are
@@ -239,7 +241,7 @@ _xfs_buf_alloc(
 	error = xfs_buf_get_maps(bp, nmaps);
 	if (error)  {
 		kmem_cache_free(xfs_buf_zone, bp);
-		return NULL;
+		return error;
 	}
 
 	bp->b_bn = map[0].bm_bn;
@@ -256,7 +258,8 @@ _xfs_buf_alloc(
 	XFS_STATS_INC(bp->b_mount, xb_create);
 	trace_xfs_buf_init(bp, _RET_IP_);
 
-	return bp;
+	*bpp = bp;
+	return 0;
 }
 
 /*
@@ -715,8 +718,8 @@ xfs_buf_get_map(
 		return NULL;
 	}
 
-	new_bp = _xfs_buf_alloc(target, map, nmaps, flags);
-	if (unlikely(!new_bp))
+	error = _xfs_buf_alloc(target, map, nmaps, flags, &new_bp);
+	if (error)
 		return NULL;
 
 	error = xfs_buf_allocate_memory(new_bp, flags);
@@ -917,8 +920,8 @@ xfs_buf_get_uncached(
 	DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);
 
 	/* flags might contain irrelevant bits, pass only what we care about */
-	bp = _xfs_buf_alloc(target, &map, 1, flags & XBF_NO_IOACCT);
-	if (unlikely(bp == NULL))
+	error = _xfs_buf_alloc(target, &map, 1, flags & XBF_NO_IOACCT, &bp);
+	if (error)
 		goto fail;
 
 	page_count = PAGE_ALIGN(numblks << BBSHIFT) >> PAGE_SHIFT;