erofs: clean up zmap.c

Several trivial cleanups which aren't quite necessary to split:

 - Rename lcluster load functions as well as justify full indexes
   since they are typically used for global deduplication for
   compressed data;

 - Avoid unnecessary lines, comments for simplicity.

No logic changes.
Reviewed-by: Guo Xuenan <guoxuenan@huaweicloud.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230615064421.103178-1-hsiangkao@linux.alibaba.com

fs/erofs/zmap.c

@@ -22,8 +22,8 @@ struct z_erofs_maprecorder {
 	bool partialref;
 };
 
-static int legacy_load_cluster_from_disk(struct z_erofs_maprecorder *m,
-					 unsigned long lcn)
+static int z_erofs_load_full_lcluster(struct z_erofs_maprecorder *m,
+				      unsigned long lcn)
 {
 	struct inode *const inode = m->inode;
 	struct erofs_inode *const vi = EROFS_I(inode);
@@ -226,8 +226,8 @@ static int unpack_compacted_index(struct z_erofs_maprecorder *m,
 	return 0;
 }
 
-static int compacted_load_cluster_from_disk(struct z_erofs_maprecorder *m,
-					    unsigned long lcn, bool lookahead)
+static int z_erofs_load_compact_lcluster(struct z_erofs_maprecorder *m,
+					 unsigned long lcn, bool lookahead)
 {
 	struct inode *const inode = m->inode;
 	struct erofs_inode *const vi = EROFS_I(inode);
@@ -277,23 +277,23 @@ static int compacted_load_cluster_from_disk(struct z_erofs_maprecorder *m,
 	return unpack_compacted_index(m, amortizedshift, pos, lookahead);
 }
 
-static int z_erofs_load_cluster_from_disk(struct z_erofs_maprecorder *m,
-					  unsigned int lcn, bool lookahead)
+static int z_erofs_load_lcluster_from_disk(struct z_erofs_maprecorder *m,
+					   unsigned int lcn, bool lookahead)
 {
-	const unsigned int datamode = EROFS_I(m->inode)->datalayout;
-
-	if (datamode == EROFS_INODE_COMPRESSED_FULL)
-		return legacy_load_cluster_from_disk(m, lcn);
-
-	if (datamode == EROFS_INODE_COMPRESSED_COMPACT)
-		return compacted_load_cluster_from_disk(m, lcn, lookahead);
-
-	return -EINVAL;
+	switch (EROFS_I(m->inode)->datalayout) {
+	case EROFS_INODE_COMPRESSED_FULL:
+		return z_erofs_load_full_lcluster(m, lcn);
+	case EROFS_INODE_COMPRESSED_COMPACT:
+		return z_erofs_load_compact_lcluster(m, lcn, lookahead);
+	default:
+		return -EINVAL;
+	}
 }
 
 static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
 				   unsigned int lookback_distance)
 {
+	struct super_block *sb = m->inode->i_sb;
 	struct erofs_inode *const vi = EROFS_I(m->inode);
 	const unsigned int lclusterbits = vi->z_logical_clusterbits;
 
@@ -301,21 +301,15 @@ static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
 		unsigned long lcn = m->lcn - lookback_distance;
 		int err;
 
-		/* load extent head logical cluster if needed */
-		err = z_erofs_load_cluster_from_disk(m, lcn, false);
+		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(m->inode->i_sb,
-					  "invalid lookback distance 0 @ nid %llu",
-					  vi->nid);
-				DBG_BUGON(1);
-				return -EFSCORRUPTED;
-			}
 			lookback_distance = m->delta[0];
+			if (!lookback_distance)
+				goto err_bogus;
 			continue;
 		case Z_EROFS_LCLUSTER_TYPE_PLAIN:
 		case Z_EROFS_LCLUSTER_TYPE_HEAD1:
@@ -324,16 +318,15 @@ static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
 			m->map->m_la = (lcn << lclusterbits) | m->clusterofs;
 			return 0;
 		default:
-			erofs_err(m->inode->i_sb,
-				  "unknown type %u @ lcn %lu of nid %llu",
+			erofs_err(sb, "unknown type %u @ lcn %lu of nid %llu",
 				  m->type, lcn, vi->nid);
 			DBG_BUGON(1);
 			return -EOPNOTSUPP;
 		}
 	}
-
-	erofs_err(m->inode->i_sb, "bogus lookback distance @ nid %llu",
-		  vi->nid);
+err_bogus:
+	erofs_err(sb, "bogus lookback distance %u @ lcn %lu of nid %llu",
+		  lookback_distance, m->lcn, vi->nid);
 	DBG_BUGON(1);
 	return -EFSCORRUPTED;
 }
@@ -365,7 +358,7 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
 	if (m->compressedblks)
 		goto out;
 
-	err = z_erofs_load_cluster_from_disk(m, lcn, false);
+	err = z_erofs_load_lcluster_from_disk(m, lcn, false);
 	if (err)
 		return err;
 
@@ -397,9 +390,8 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
 			break;
 		fallthrough;
 	default:
-		erofs_err(m->inode->i_sb,
-			  "cannot found CBLKCNT @ lcn %lu of nid %llu",
-			  lcn, vi->nid);
+		erofs_err(sb, "cannot found CBLKCNT @ lcn %lu of nid %llu", lcn,
+			  vi->nid);
 		DBG_BUGON(1);
 		return -EFSCORRUPTED;
 	}
@@ -407,9 +399,7 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
 	map->m_plen = erofs_pos(sb, m->compressedblks);
 	return 0;
 err_bonus_cblkcnt:
-	erofs_err(m->inode->i_sb,
-		  "bogus CBLKCNT @ lcn %lu of nid %llu",
-		  lcn, vi->nid);
+	erofs_err(sb, "bogus CBLKCNT @ lcn %lu of nid %llu", lcn, vi->nid);
 	DBG_BUGON(1);
 	return -EFSCORRUPTED;
 }
@@ -430,7 +420,7 @@ static int z_erofs_get_extent_decompressedlen(struct z_erofs_maprecorder *m)
 			return 0;
 		}
 
-		err = z_erofs_load_cluster_from_disk(m, lcn, true);
+		err = z_erofs_load_lcluster_from_disk(m, lcn, true);
 		if (err)
 			return err;
 
@@ -477,7 +467,7 @@ static int z_erofs_do_map_blocks(struct inode *inode,
 	initial_lcn = ofs >> lclusterbits;
 	endoff = ofs & ((1 << lclusterbits) - 1);
 
-	err = z_erofs_load_cluster_from_disk(&m, initial_lcn, false);
+	err = z_erofs_load_lcluster_from_disk(&m, initial_lcn, false);
 	if (err)
 		goto unmap_out;
 
@@ -535,8 +525,7 @@ static int z_erofs_do_map_blocks(struct inode *inode,
 	if (flags & EROFS_GET_BLOCKS_FINDTAIL) {
 		vi->z_tailextent_headlcn = m.lcn;
 		/* for non-compact indexes, fragmentoff is 64 bits */
-		if (fragment &&
-		    vi->datalayout == EROFS_INODE_COMPRESSED_FULL)
+		if (fragment && vi->datalayout == EROFS_INODE_COMPRESSED_FULL)
 			vi->z_fragmentoff |= (u64)m.pblk << 32;
 	}
 	if (ztailpacking && m.lcn == vi->z_tailextent_headlcn) {