xfs: use xfs_buf_alloc_pages for uncached buffers

Use the newly factored out page allocation code. This adds
automatic buffer zeroing for non-read uncached buffers.

This also allows us to greatly simply the error handling in
xfs_buf_get_uncached(). Because xfs_buf_alloc_pages() cleans up
partial allocation failure, we can just call xfs_buf_free() in all
error cases now to clean up after failures.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/libxfs/xfs_ag.c

@@ -43,7 +43,6 @@ xfs_get_aghdr_buf(
 	if (error)
 		return error;
 
-	xfs_buf_zero(bp, 0, BBTOB(bp->b_length));
 	bp->b_bn = blkno;
 	bp->b_maps[0].bm_bn = blkno;
 	bp->b_ops = ops;

fs/xfs/xfs_buf.c

@@ -973,7 +973,7 @@ xfs_buf_get_uncached(
 	struct xfs_buf		**bpp)
 {
 	unsigned long		page_count;
-	int			error, i;
+	int			error;
 	struct xfs_buf		*bp;
 	DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks);
 
@@ -982,41 +982,26 @@ xfs_buf_get_uncached(
 	/* flags might contain irrelevant bits, pass only what we care about */
 	error = _xfs_buf_alloc(target, &map, 1, flags & XBF_NO_IOACCT, &bp);
 	if (error)
-		goto fail;
+		return error;
 
 	page_count = PAGE_ALIGN(numblks << BBSHIFT) >> PAGE_SHIFT;
-	error = _xfs_buf_get_pages(bp, page_count);
+	error = xfs_buf_alloc_pages(bp, page_count, flags);
 	if (error)
 		goto fail_free_buf;
 
-	for (i = 0; i < page_count; i++) {
-		bp->b_pages[i] = alloc_page(xb_to_gfp(flags));
-		if (!bp->b_pages[i]) {
-			error = -ENOMEM;
-			goto fail_free_mem;
-		}
-	}
-	bp->b_flags |= _XBF_PAGES;
-
 	error = _xfs_buf_map_pages(bp, 0);
 	if (unlikely(error)) {
 		xfs_warn(target->bt_mount,
 			"%s: failed to map pages", __func__);
-		goto fail_free_mem;
+		goto fail_free_buf;
 	}
 
 	trace_xfs_buf_get_uncached(bp, _RET_IP_);
 	*bpp = bp;
 	return 0;
 
- fail_free_mem:
-	while (--i >= 0)
-		__free_page(bp->b_pages[i]);
-	_xfs_buf_free_pages(bp);
- fail_free_buf:
-	xfs_buf_free_maps(bp);
-	kmem_cache_free(xfs_buf_zone, bp);
- fail:
+fail_free_buf:
+	xfs_buf_free(bp);
 	return error;
 }