[PATCH 9/9] erofs-utils: lib: clean up z_erofs_extent_lookback

[Gao Xiang]

Source kernel commit: ab474fccd04509db89fde8d3b28c39aa9a47db64
Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
 lib/zmap.c | 60 ++++++++++++++++++++++++------------------------------
 1 file changed, 27 insertions(+), 33 deletions(-)

diff --git a/lib/zmap.c b/lib/zmap.c
index 24bdff7..2287bed 100644
--- a/lib/zmap.c
+++ b/lib/zmap.c
@@ -273,46 +273,40 @@ static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
 				   unsigned int lookback_distance)
 {
 	struct erofs_inode *const vi = m->inode;
-	struct erofs_map_blocks *const map = m->map;
 	const unsigned int lclusterbits = vi->z_logical_clusterbits;
-	unsigned long lcn = m->lcn;
-	int err;
 
-	if (lcn < lookback_distance) {
-		erofs_err("bogus lookback distance @ nid %llu",
-			  (unsigned long long)vi->nid);
-		DBG_BUGON(1);
-		return -EFSCORRUPTED;
-	}
+	while (m->lcn >= lookback_distance) {
+		unsigned long lcn = m->lcn - lookback_distance;
+		int err;
 
-	/* load extent head logical cluster if needed */
-	lcn -= lookback_distance;
-	err = z_erofs_load_lcluster_from_disk(m, lcn, false);
-	if (err)
-		return err;
+		err = z_erofs_load_lcluster_from_disk(m, lcn, false);
+		if (err)
+			return err;
 
-	switch (m->type) {
-	case Z_EROFS_LCLUSTER_TYPE_NONHEAD:
-		if (!m->delta[0]) {
-			erofs_err("invalid lookback distance 0 @ nid %llu",
-				  (unsigned long long)vi->nid);
+		switch (m->type) {
+		case Z_EROFS_LCLUSTER_TYPE_NONHEAD:
+			lookback_distance = m->delta[0];
+			if (!lookback_distance)
+				goto err_bogus;
+			continue;
+		case Z_EROFS_LCLUSTER_TYPE_PLAIN:
+		case Z_EROFS_LCLUSTER_TYPE_HEAD1:
+		case Z_EROFS_LCLUSTER_TYPE_HEAD2:
+			m->headtype = m->type;
+			m->map->m_la = (lcn << lclusterbits) | m->clusterofs;
+			return 0;
+		default:
+			erofs_err("unknown type %u @ lcn %lu of nid %llu",
+				  m->type, lcn, vi->nid | 0ULL);
 			DBG_BUGON(1);
-			return -EFSCORRUPTED;
+			return -EOPNOTSUPP;
 		}
-		return z_erofs_extent_lookback(m, m->delta[0]);
-	case Z_EROFS_LCLUSTER_TYPE_PLAIN:
-	case Z_EROFS_LCLUSTER_TYPE_HEAD1:
-	case Z_EROFS_LCLUSTER_TYPE_HEAD2:
-		m->headtype = m->type;
-		map->m_la = (lcn << lclusterbits) | m->clusterofs;
-		break;
-	default:
-		erofs_err("unknown type %u @ lcn %lu of nid %llu",
-			  m->type, lcn, (unsigned long long)vi->nid);
-		DBG_BUGON(1);
-		return -EOPNOTSUPP;
 	}
-	return 0;
+err_bogus:
+	erofs_err("bogus lookback distance %u @ lcn %lu of nid %llu",
+		  lookback_distance, m->lcn | 0ULL, vi->nid);
+	DBG_BUGON(1);
+	return -EFSCORRUPTED;
 }
 
 static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
-- 
2.43.5