erofs: simplify tail inline pcluster handling

Use `z_idata_size != 0` to indicate that ztailpacking is enabled.
`Z_EROFS_ADVISE_INLINE_PCLUSTER` cannot be ignored, as `h_idata_size`
could be non-zero prior to erofs-utils 1.6 [1].

Additionally, merge `z_idataoff` and `z_fragmentoff` since these two
features are mutually exclusive for a given inode.

[1] https://git.kernel.org/xiang/erofs-utils/c/547bea3cb71a
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250225114038.3259726-1-hsiangkao@linux.alibaba.com

Author: hsiangkao

fs/erofs/internal.h

@@ -263,13 +263,8 @@ struct erofs_inode {
 			unsigned char  z_algorithmtype[2];
 			unsigned char  z_logical_clusterbits;
 			unsigned long  z_tailextent_headlcn;
-			union {
-				struct {
-					erofs_off_t    z_idataoff;
-					unsigned short z_idata_size;
-				};
-				erofs_off_t z_fragmentoff;
-			};
+			erofs_off_t    z_fragmentoff;
+			unsigned short z_idata_size;
 		};
 #endif	/* CONFIG_EROFS_FS_ZIP */
 	};

fs/erofs/zmap.c

@@ -395,8 +395,8 @@ static int z_erofs_do_map_blocks(struct inode *inode,
 				 struct erofs_map_blocks *map, int flags)
 {
 	struct erofs_inode *const vi = EROFS_I(inode);
-	bool ztailpacking = vi->z_advise & Z_EROFS_ADVISE_INLINE_PCLUSTER;
 	bool fragment = vi->z_advise & Z_EROFS_ADVISE_FRAGMENT_PCLUSTER;
+	bool ztailpacking = vi->z_idata_size;
 	struct z_erofs_maprecorder m = {
 		.inode = inode,
 		.map = map,
@@ -415,9 +415,8 @@ static int z_erofs_do_map_blocks(struct inode *inode,
 	if (err)
 		goto unmap_out;
 
-	if (ztailpacking && (flags & EROFS_GET_BLOCKS_FINDTAIL))
-		vi->z_idataoff = m.nextpackoff;
-
+	if ((flags & EROFS_GET_BLOCKS_FINDTAIL) && ztailpacking)
+		vi->z_fragmentoff = m.nextpackoff;
 	map->m_flags = EROFS_MAP_MAPPED | EROFS_MAP_ENCODED;
 	end = (m.lcn + 1ULL) << lclusterbits;
 
@@ -472,7 +471,7 @@ static int z_erofs_do_map_blocks(struct inode *inode,
 	}
 	if (ztailpacking && m.lcn == vi->z_tailextent_headlcn) {
 		map->m_flags |= EROFS_MAP_META;
-		map->m_pa = vi->z_idataoff;
+		map->m_pa = vi->z_fragmentoff;
 		map->m_plen = vi->z_idata_size;
 	} else if (fragment && m.lcn == vi->z_tailextent_headlcn) {
 		map->m_flags |= EROFS_MAP_FRAGMENT;
@@ -565,6 +564,10 @@ static int z_erofs_fill_inode_lazy(struct inode *inode)
 	vi->z_advise = le16_to_cpu(h->h_advise);
 	vi->z_algorithmtype[0] = h->h_algorithmtype & 15;
 	vi->z_algorithmtype[1] = h->h_algorithmtype >> 4;
+	if (vi->z_advise & Z_EROFS_ADVISE_FRAGMENT_PCLUSTER)
+		vi->z_fragmentoff = le32_to_cpu(h->h_fragmentoff);
+	else if (vi->z_advise & Z_EROFS_ADVISE_INLINE_PCLUSTER)
+		vi->z_idata_size = le16_to_cpu(h->h_idata_size);
 
 	headnr = 0;
 	if (vi->z_algorithmtype[0] >= Z_EROFS_COMPRESSION_MAX ||
@@ -593,18 +596,16 @@ static int z_erofs_fill_inode_lazy(struct inode *inode)
 		goto out_put_metabuf;
 	}
 
-	if (vi->z_advise & Z_EROFS_ADVISE_INLINE_PCLUSTER) {
+	if (vi->z_idata_size) {
 		struct erofs_map_blocks map = {
 			.buf = __EROFS_BUF_INITIALIZER
 		};
 
-		vi->z_idata_size = le16_to_cpu(h->h_idata_size);
 		err = z_erofs_do_map_blocks(inode, &map,
 					    EROFS_GET_BLOCKS_FINDTAIL);
 		erofs_put_metabuf(&map.buf);
 
-		if (!map.m_plen ||
-		    erofs_blkoff(sb, map.m_pa) + map.m_plen > sb->s_blocksize) {
+		if (erofs_blkoff(sb, map.m_pa) + map.m_plen > sb->s_blocksize) {
 			erofs_err(sb, "invalid tail-packing pclustersize %llu",
 				  map.m_plen);
 			err = -EFSCORRUPTED;
@@ -619,7 +620,6 @@ static int z_erofs_fill_inode_lazy(struct inode *inode)
 			.buf = __EROFS_BUF_INITIALIZER
 		};
 
-		vi->z_fragmentoff = le32_to_cpu(h->h_fragmentoff);
 		err = z_erofs_do_map_blocks(inode, &map,
 					    EROFS_GET_BLOCKS_FINDTAIL);
 		erofs_put_metabuf(&map.buf);