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

[Gao Xiang]

Source kernel commit: ab474fccd04509db89fde8d3b28c39aa9a47db64
Signed-off-by: Gao Xiang <hsiang...@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