erofs: get compression algorithms directly on mapping

Currently, z_erofs_map_blocks_iter() returns whether extents are
compressed or not, and the decompression frontend gets the specific
algorithms then.

It works but not quite well in many aspests, for example:
 - The decompression frontend has to deal with whether extents are
   compressed or not again and lookup the algorithms if compressed.
   It's duplicated and too detailed about the on-disk mapping.

 - A new secondary compression head will be introduced later so that
   each file can have 2 compression algorithms at most for different
   type of data. It could increase the complexity of the decompression
   frontend if still handled in this way;

 - A new readmore decompression strategy will be introduced to get
   better performance for much bigger pcluster and lzma, which needs
   the specific algorithm in advance as well.

Let's look up compression algorithms in z_erofs_map_blocks_iter()
directly instead.

Link: https://lore.kernel.org/r/20211008200839.24541-2-xiang@kernel.orgReviewed-by: Chao Yu <chao@kernel.org>
Reviewed-by: Yue Hu <huyue2@yulong.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/compress.h

@@ -8,11 +8,6 @@
 
 #include "internal.h"
 
-enum {
-	Z_EROFS_COMPRESSION_SHIFTED = Z_EROFS_COMPRESSION_MAX,
-	Z_EROFS_COMPRESSION_RUNTIME_MAX
-};
-
 struct z_erofs_decompress_req {
 	struct super_block *sb;
 	struct page **in, **out;

fs/erofs/internal.h

@@ -363,7 +363,7 @@ extern const struct address_space_operations z_erofs_aops;
  * of the corresponding uncompressed data in the file.
  */
 enum {
-	BH_Zipped = BH_PrivateStart,
+	BH_Encoded = BH_PrivateStart,
 	BH_FullMapped,
 };
 
@@ -371,8 +371,8 @@ enum {
 #define EROFS_MAP_MAPPED	(1 << BH_Mapped)
 /* Located in metadata (could be copied from bd_inode) */
 #define EROFS_MAP_META		(1 << BH_Meta)
-/* The extent has been compressed */
-#define EROFS_MAP_ZIPPED	(1 << BH_Zipped)
+/* The extent is encoded */
+#define EROFS_MAP_ENCODED	(1 << BH_Encoded)
 /* The length of extent is full */
 #define EROFS_MAP_FULL_MAPPED	(1 << BH_FullMapped)
 
@@ -381,6 +381,7 @@ struct erofs_map_blocks {
 	u64 m_plen, m_llen;
 
 	unsigned short m_deviceid;
+	char m_algorithmformat;
 	unsigned int m_flags;
 
 	struct page *mpage;
@@ -394,6 +395,11 @@ struct erofs_map_blocks {
  */
 #define EROFS_GET_BLOCKS_FIEMAP	0x0002
 
+enum {
+	Z_EROFS_COMPRESSION_SHIFTED = Z_EROFS_COMPRESSION_MAX,
+	Z_EROFS_COMPRESSION_RUNTIME_MAX
+};
+
 /* zmap.c */
 extern const struct iomap_ops z_erofs_iomap_report_ops;
 

fs/erofs/zdata.c

@@ -476,6 +476,11 @@ static int z_erofs_register_collection(struct z_erofs_collector *clt,
 	struct erofs_workgroup *grp;
 	int err;
 
+	if (!(map->m_flags & EROFS_MAP_ENCODED)) {
+		DBG_BUGON(1);
+		return -EFSCORRUPTED;
+	}
+
 	/* no available pcluster, let's allocate one */
 	pcl = z_erofs_alloc_pcluster(map->m_plen >> PAGE_SHIFT);
 	if (IS_ERR(pcl))
@@ -483,16 +488,11 @@ static int z_erofs_register_collection(struct z_erofs_collector *clt,
 
 	atomic_set(&pcl->obj.refcount, 1);
 	pcl->obj.index = map->m_pa >> PAGE_SHIFT;
-
+	pcl->algorithmformat = map->m_algorithmformat;
 	pcl->length = (map->m_llen << Z_EROFS_PCLUSTER_LENGTH_BIT) |
 		(map->m_flags & EROFS_MAP_FULL_MAPPED ?
 			Z_EROFS_PCLUSTER_FULL_LENGTH : 0);
 
-	if (map->m_flags & EROFS_MAP_ZIPPED)
-		pcl->algorithmformat = Z_EROFS_COMPRESSION_LZ4;
-	else
-		pcl->algorithmformat = Z_EROFS_COMPRESSION_SHIFTED;
-
 	/* new pclusters should be claimed as type 1, primary and followed */
 	pcl->next = clt->owned_head;
 	clt->mode = COLLECT_PRIMARY_FOLLOWED;

fs/erofs/zmap.c

@@ -111,7 +111,7 @@ struct z_erofs_maprecorder {
 
 	unsigned long lcn;
 	/* compression extent information gathered */
-	u8  type;
+	u8  type, headtype;
 	u16 clusterofs;
 	u16 delta[2];
 	erofs_blk_t pblk, compressedlcs;
@@ -446,9 +446,8 @@ static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
 		}
 		return z_erofs_extent_lookback(m, m->delta[0]);
 	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
-		map->m_flags &= ~EROFS_MAP_ZIPPED;
-		fallthrough;
 	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
+		m->headtype = m->type;
 		map->m_la = (lcn << lclusterbits) | m->clusterofs;
 		break;
 	default:
@@ -472,7 +471,7 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
 
 	DBG_BUGON(m->type != Z_EROFS_VLE_CLUSTER_TYPE_PLAIN &&
 		  m->type != Z_EROFS_VLE_CLUSTER_TYPE_HEAD);
-	if (!(map->m_flags & EROFS_MAP_ZIPPED) ||
+	if (m->headtype == Z_EROFS_VLE_CLUSTER_TYPE_PLAIN ||
 	    !(vi->z_advise & Z_EROFS_ADVISE_BIG_PCLUSTER_1)) {
 		map->m_plen = 1 << lclusterbits;
 		return 0;
@@ -609,16 +608,14 @@ int z_erofs_map_blocks_iter(struct inode *inode,
 	if (err)
 		goto unmap_out;
 
-	map->m_flags = EROFS_MAP_ZIPPED;	/* by default, compressed */
+	map->m_flags = EROFS_MAP_MAPPED | EROFS_MAP_ENCODED;
 	end = (m.lcn + 1ULL) << lclusterbits;
 
 	switch (m.type) {
 	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
-		if (endoff >= m.clusterofs)
-			map->m_flags &= ~EROFS_MAP_ZIPPED;
-		fallthrough;
 	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
 		if (endoff >= m.clusterofs) {
+			m.headtype = m.type;
 			map->m_la = (m.lcn << lclusterbits) | m.clusterofs;
 			break;
 		}
@@ -650,12 +647,16 @@ int z_erofs_map_blocks_iter(struct inode *inode,
 
 	map->m_llen = end - map->m_la;
 	map->m_pa = blknr_to_addr(m.pblk);
-	map->m_flags |= EROFS_MAP_MAPPED;
 
 	err = z_erofs_get_extent_compressedlen(&m, initial_lcn);
 	if (err)
 		goto out;
 
+	if (m.headtype == Z_EROFS_VLE_CLUSTER_TYPE_PLAIN)
+		map->m_algorithmformat = Z_EROFS_COMPRESSION_SHIFTED;
+	else
+		map->m_algorithmformat = vi->z_algorithmtype[0];
+
 	if (flags & EROFS_GET_BLOCKS_FIEMAP) {
 		err = z_erofs_get_extent_decompressedlen(&m);
 		if (!err)

include/trace/events/erofs.h

@@ -24,7 +24,7 @@ struct erofs_map_blocks;
 #define show_mflags(flags) __print_flags(flags, "",	\
 	{ EROFS_MAP_MAPPED,	"M" },			\
 	{ EROFS_MAP_META,	"I" },			\
-	{ EROFS_MAP_ZIPPED,	"Z" })
+	{ EROFS_MAP_ENCODED,	"E" })
 
 TRACE_EVENT(erofs_lookup,