xfs: randomly do sparse inode allocations in DEBUG mode

Sparse inode allocations generally only occur when full inode chunk
allocation fails. This requires some level of filesystem space usage and
fragmentation.

For filesystems formatted with sparse inode chunks enabled, do random
sparse inode chunk allocs when compiled in DEBUG mode to increase test
coverage.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/libxfs/xfs_ialloc.c

@@ -607,9 +607,18 @@ xfs_ialloc_ag_alloc(
 	struct xfs_inobt_rec_incore rec;
 	struct xfs_perag *pag;
 
+	int		do_sparse = 0;
+
+#ifdef DEBUG
+	/* randomly do sparse inode allocations */
+	if (xfs_sb_version_hassparseinodes(&tp->t_mountp->m_sb))
+		do_sparse = prandom_u32() & 1;
+#endif
+
 	memset(&args, 0, sizeof(args));
 	args.tp = tp;
 	args.mp = tp->t_mountp;
+	args.fsbno = NULLFSBLOCK;
 
 	/*
 	 * Locking will ensure that we don't have two callers in here
@@ -631,6 +640,8 @@ xfs_ialloc_ag_alloc(
 	agno = be32_to_cpu(agi->agi_seqno);
 	args.agbno = XFS_AGINO_TO_AGBNO(args.mp, newino) +
 		     args.mp->m_ialloc_blks;
+	if (do_sparse)
+		goto sparse_alloc;
 	if (likely(newino != NULLAGINO &&
 		  (args.agbno < be32_to_cpu(agi->agi_length)))) {
 		args.fsbno = XFS_AGB_TO_FSB(args.mp, agno, args.agbno);
@@ -669,8 +680,7 @@ xfs_ialloc_ag_alloc(
 		 * subsequent requests.
 		 */
 		args.minalignslop = 0;
-	} else
-		args.fsbno = NULLFSBLOCK;
+	}
 
 	if (unlikely(args.fsbno == NULLFSBLOCK)) {
 		/*
@@ -728,6 +738,7 @@ xfs_ialloc_ag_alloc(
 	if (xfs_sb_version_hassparseinodes(&args.mp->m_sb) &&
 	    args.mp->m_ialloc_min_blks < args.mp->m_ialloc_blks &&
 	    args.fsbno == NULLFSBLOCK) {
+sparse_alloc:
 		args.type = XFS_ALLOCTYPE_NEAR_BNO;
 		args.agbno = be32_to_cpu(agi->agi_root);
 		args.fsbno = XFS_AGB_TO_FSB(args.mp, agno, args.agbno);