xfs: factor xfs_alloc_vextent_this_ag() for _iterate_ags()

The core of the per-ag iteration is effectively doing a "this ag"
allocation on one AG at a time. Use the same code to implement the
core "this ag" allocation in both xfs_alloc_vextent_this_ag()
and xfs_alloc_vextent_iterate_ags().

This means we only call xfs_alloc_ag_vextent() from one place so we
can easily collapse the call stack in future patches.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/libxfs/xfs_alloc.c

@@ -3244,6 +3244,28 @@ xfs_alloc_vextent_set_fsbno(
 /*
  * Allocate within a single AG only.
  */
+static int
+__xfs_alloc_vextent_this_ag(
+	struct xfs_alloc_arg	*args)
+{
+	struct xfs_mount	*mp = args->mp;
+	int			error;
+
+	error = xfs_alloc_fix_freelist(args, 0);
+	if (error) {
+		trace_xfs_alloc_vextent_nofix(args);
+		return error;
+	}
+	if (!args->agbp) {
+		/* cannot allocate in this AG at all */
+		trace_xfs_alloc_vextent_noagbp(args);
+		args->agbno = NULLAGBLOCK;
+		return 0;
+	}
+	args->agbno = XFS_FSB_TO_AGBNO(mp, args->fsbno);
+	return xfs_alloc_ag_vextent(args);
+}
+
 static int
 xfs_alloc_vextent_this_ag(
 	struct xfs_alloc_arg	*args,
@@ -3267,21 +3289,9 @@ xfs_alloc_vextent_this_ag(
 	}
 
 	args->pag = xfs_perag_get(mp, args->agno);
-	error = xfs_alloc_fix_freelist(args, 0);
-	if (error) {
-		trace_xfs_alloc_vextent_nofix(args);
-		goto out_error;
-	}
-	if (!args->agbp) {
-		trace_xfs_alloc_vextent_noagbp(args);
-		args->fsbno = NULLFSBLOCK;
-		goto out_error;
-	}
-	args->agbno = XFS_FSB_TO_AGBNO(mp, args->fsbno);
-	error = xfs_alloc_ag_vextent(args);
+	error = __xfs_alloc_vextent_this_ag(args);
 
 	xfs_alloc_vextent_set_fsbno(args, minimum_agno);
-out_error:
 	xfs_perag_put(args->pag);
 	return error;
 }
@@ -3319,24 +3329,16 @@ xfs_alloc_vextent_iterate_ags(
 	args->agno = start_agno;
 	for (;;) {
 		args->pag = xfs_perag_get(mp, args->agno);
-		error = xfs_alloc_fix_freelist(args, flags);
+		error = __xfs_alloc_vextent_this_ag(args);
 		if (error) {
-			trace_xfs_alloc_vextent_nofix(args);
+			args->agbno = NULLAGBLOCK;
 			break;
 		}
-		/*
-		 * If we get a buffer back then the allocation will fly.
-		 */
-		if (args->agbp) {
-			error = xfs_alloc_ag_vextent(args);
+		if (args->agbp)
 			break;
-		}
 
 		trace_xfs_alloc_vextent_loopfailed(args);
 
-		/*
-		 * Didn't work, figure out the next iteration.
-		 */
 		if (args->agno == start_agno &&
 		    args->otype == XFS_ALLOCTYPE_START_BNO)
 			args->type = XFS_ALLOCTYPE_THIS_AG;