erofs: refine z_erofs_get_extent_compressedlen()

 - Set `compressedblks = 1` directly for non-bigpcluster cases.  This
   simplifies the logic a bit since lcluster sizes larger than one block
   are unsupported and the details remain unclear.

 - For Z_EROFS_LCLUSTER_TYPE_PLAIN pclusters, avoid assuming
   `compressedblks = 1` by default.  Instead, check if
   Z_EROFS_ADVISE_BIG_PCLUSTER_2 is set.

It basically has no impact to existing valid images, but it's useful to
find the gap to prepare for large PLAIN pclusters.

Link: https://lore.kernel.org/r/20250123090109.973463-1-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index b9e35089c9b8de317f45162bc840de56321fa3b7..689437e99a5a3483b2a894e9972c5e61fedee377 100644 (file)
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -294,27 +294,23 @@ err_bogus:
 static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
                                            unsigned int initial_lcn)
 {
-       struct super_block *sb = m->inode->i_sb;
-       struct erofs_inode *const vi = EROFS_I(m->inode);
-       struct erofs_map_blocks *const map = m->map;
-       const unsigned int lclusterbits = vi->z_logical_clusterbits;
-       unsigned long lcn;
+       struct inode *inode = m->inode;
+       struct super_block *sb = inode->i_sb;
+       struct erofs_inode *vi = EROFS_I(inode);
+       bool bigpcl1 = vi->z_advise & Z_EROFS_ADVISE_BIG_PCLUSTER_1;
+       bool bigpcl2 = vi->z_advise & Z_EROFS_ADVISE_BIG_PCLUSTER_2;
+       unsigned long lcn = m->lcn + 1;
        int err;
 
-       DBG_BUGON(m->type != Z_EROFS_LCLUSTER_TYPE_PLAIN &&
-                 m->type != Z_EROFS_LCLUSTER_TYPE_HEAD1 &&
-                 m->type != Z_EROFS_LCLUSTER_TYPE_HEAD2);
+       DBG_BUGON(m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD);
        DBG_BUGON(m->type != m->headtype);
 
-       if (m->headtype == Z_EROFS_LCLUSTER_TYPE_PLAIN ||
-           ((m->headtype == Z_EROFS_LCLUSTER_TYPE_HEAD1) &&
-            !(vi->z_advise & Z_EROFS_ADVISE_BIG_PCLUSTER_1)) ||
-           ((m->headtype == Z_EROFS_LCLUSTER_TYPE_HEAD2) &&
-            !(vi->z_advise & Z_EROFS_ADVISE_BIG_PCLUSTER_2))) {
-               map->m_plen = 1ULL << lclusterbits;
-               return 0;
-       }
-       lcn = m->lcn + 1;
+       if ((m->headtype == Z_EROFS_LCLUSTER_TYPE_HEAD1 && !bigpcl1) ||
+           ((m->headtype == Z_EROFS_LCLUSTER_TYPE_PLAIN ||
+             m->headtype == Z_EROFS_LCLUSTER_TYPE_HEAD2) && !bigpcl2) ||
+           (lcn << vi->z_logical_clusterbits) >= inode->i_size)
+               m->compressedblks = 1;
+
        if (m->compressedblks)
                goto out;
 
@@ -339,9 +335,9 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
        case Z_EROFS_LCLUSTER_TYPE_HEAD2:
                /*
                 * if the 1st NONHEAD lcluster is actually PLAIN or HEAD type
-                * rather than CBLKCNT, it's a 1 lcluster-sized pcluster.
+                * rather than CBLKCNT, it's a 1 block-sized pcluster.
                 */
-               m->compressedblks = 1 << (lclusterbits - sb->s_blocksize_bits);
+               m->compressedblks = 1;
                break;
        case Z_EROFS_LCLUSTER_TYPE_NONHEAD:
                if (m->delta[0] != 1)
@@ -356,7 +352,7 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
                return -EFSCORRUPTED;
        }
 out:
-       map->m_plen = erofs_pos(sb, m->compressedblks);
+       m->map->m_plen = erofs_pos(sb, m->compressedblks);
        return 0;
 err_bonus_cblkcnt:
        erofs_err(sb, "bogus CBLKCNT @ lcn %lu of nid %llu", lcn, vi->nid);