[RFC PATCH 2/4] xfs: check ag is empty

[Gao Xiang <hsiangkao@redhat.com>]

After a perag is stableized as inactive, we could check if such ag
is empty. In order to achieve that, AGFL is also needed to be
emptified in advance to make sure that only one freespace extent
will exist here.

Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
---
 fs/xfs/libxfs/xfs_alloc.c | 97 +++++++++++++++++++++++++++++++++++++++
 fs/xfs/libxfs/xfs_alloc.h |  4 ++
 2 files changed, 101 insertions(+)

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index 01d4e4d4c1d6..60a8c134c00e 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -2474,6 +2474,103 @@ xfs_defer_agfl_block(
 	xfs_defer_add(tp, XFS_DEFER_OPS_TYPE_AGFL_FREE, &new->xefi_list);
 }
 
+int
+xfs_ag_emptify_agfl(
+	struct xfs_buf		*agfbp)
+{
+	struct xfs_mount	*mp = agfbp->b_mount;
+	struct xfs_perag	*pag = agfbp->b_pag;
+	struct xfs_trans	*tp;
+	int			error;
+	struct xfs_owner_info	oinfo = XFS_RMAP_OINFO_AG;
+
+	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_growdata, 0, 0,
+				XFS_TRANS_RESERVE, &tp);
+	if (error)
+		return error;
+
+	/* attach to the transaction and keep it from unlocked */
+	xfs_trans_bjoin(tp, agfbp);
+	xfs_trans_bhold(tp, agfbp);
+
+	while (pag->pagf_flcount) {
+		xfs_agblock_t	bno;
+		int		error;
+
+		error = xfs_alloc_get_freelist(tp, agfbp, &bno, 0);
+		if (error)
+			break;
+
+		ASSERT(bno != NULLAGBLOCK);
+		xfs_defer_agfl_block(tp, pag->pag_agno, bno, &oinfo);
+	}
+	xfs_trans_set_sync(tp);
+	xfs_trans_commit(tp);
+	return error;
+}
+
+int
+xfs_ag_is_empty(
+	struct xfs_buf		*agfbp)
+{
+	struct xfs_mount	*mp = agfbp->b_mount;
+	struct xfs_perag	*pag = agfbp->b_pag;
+	struct xfs_agf		*agf = agfbp->b_addr;
+	struct xfs_btree_cur	*cnt_cur;
+	xfs_agblock_t		nfbno;
+	xfs_extlen_t		nflen;
+	int			error, i;
+
+	if (!pag->pag_inactive)
+		return -EINVAL;
+
+	if (pag->pagf_freeblks + pag->pagf_flcount !=
+	    be32_to_cpu(agf->agf_length) - mp->m_ag_prealloc_blocks)
+		return -ENOTEMPTY;
+
+	if (pag->pagf_flcount) {
+		error = xfs_ag_emptify_agfl(agfbp);
+		if (error)
+			return error;
+
+		if (pag->pagf_freeblks !=
+		    be32_to_cpu(agf->agf_length) - mp->m_ag_prealloc_blocks)
+			return -ENOTEMPTY;
+	}
+
+	if (pag->pagi_count > 0 || pag->pagi_freecount > 0)
+		return -ENOTEMPTY;
+
+	if (be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) > 1 ||
+	    be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNT]) > 1)
+		return -ENOTEMPTY;
+
+	cnt_cur = xfs_allocbt_init_cursor(mp, NULL, agfbp,
+					  pag->pag_agno, XFS_BTNUM_CNT);
+	ASSERT(cnt_cur->bc_nlevels == 1);
+	error = xfs_alloc_lookup_ge(cnt_cur, 0,
+				    be32_to_cpu(agf->agf_longest), &i);
+	if (error || !i)
+		goto out;
+
+	error = xfs_alloc_get_rec(cnt_cur, &nfbno, &nflen, &i);
+	if (error)
+		goto out;
+
+	if (XFS_IS_CORRUPT(mp, i != 1)) {
+		error = -EFSCORRUPTED;
+		goto out;
+	}
+
+	error = -ENOTEMPTY;
+	if (nfbno == mp->m_ag_prealloc_blocks &&
+	    nflen == pag->pagf_freeblks)
+		error = 0;
+out:
+	xfs_btree_del_cursor(cnt_cur, XFS_BTREE_NOERROR);
+	return error;
+}
+
 #ifdef DEBUG
 /*
  * Check if an AGF has a free extent record whose length is equal to
diff --git a/fs/xfs/libxfs/xfs_alloc.h b/fs/xfs/libxfs/xfs_alloc.h
index a4427c5775c2..a7015b971075 100644
--- a/fs/xfs/libxfs/xfs_alloc.h
+++ b/fs/xfs/libxfs/xfs_alloc.h
@@ -156,6 +156,10 @@ xfs_alloc_read_agf(
 	int		flags,		/* XFS_ALLOC_FLAG_... */
 	struct xfs_buf	**bpp);		/* buffer for the ag freelist header */
 
+int
+xfs_ag_is_empty(
+	struct xfs_buf		*agfbp);
+
 /*
  * Allocate an extent (variable-size).
  */
-- 
2.27.0