erofs: introduce partial-referenced pclusters

Due to deduplication for compressed data, pclusters can be partially
referenced with their prefixes.

Together with the user-space implementation, it enables EROFS
variable-length global compressed data deduplication with rolling
hash.

Link: https://lore.kernel.org/r/20220923014915.4362-1-hsiangkao@linux.alibaba.comReviewed-by: Yue Hu <huyue2@coolpad.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/decompressor_lzma.c

@@ -217,6 +217,9 @@ int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
 			strm->buf.out_size = min_t(u32, outlen,
 						   PAGE_SIZE - pageofs);
 			outlen -= strm->buf.out_size;
+			if (!rq->out[no] && rq->fillgaps)	/* deduped */
+				rq->out[no] = erofs_allocpage(pagepool,
+						GFP_KERNEL | __GFP_NOFAIL);
 			if (rq->out[no])
 				strm->buf.out = kmap(rq->out[no]) + pageofs;
 			pageofs = 0;

fs/erofs/erofs_fs.h

@@ -26,6 +26,7 @@
 #define EROFS_FEATURE_INCOMPAT_COMPR_HEAD2	0x00000008
 #define EROFS_FEATURE_INCOMPAT_ZTAILPACKING	0x00000010
 #define EROFS_FEATURE_INCOMPAT_FRAGMENTS	0x00000020
+#define EROFS_FEATURE_INCOMPAT_DEDUPE		0x00000020
 #define EROFS_ALL_FEATURE_INCOMPAT		\
 	(EROFS_FEATURE_INCOMPAT_ZERO_PADDING | \
 	 EROFS_FEATURE_INCOMPAT_COMPR_CFGS | \
@@ -34,7 +35,8 @@
 	 EROFS_FEATURE_INCOMPAT_DEVICE_TABLE | \
 	 EROFS_FEATURE_INCOMPAT_COMPR_HEAD2 | \
 	 EROFS_FEATURE_INCOMPAT_ZTAILPACKING | \
-	 EROFS_FEATURE_INCOMPAT_FRAGMENTS)
+	 EROFS_FEATURE_INCOMPAT_FRAGMENTS | \
+	 EROFS_FEATURE_INCOMPAT_DEDUPE)
 
 #define EROFS_SB_EXTSLOT_SIZE	16
 
@@ -371,6 +373,9 @@ enum {
 #define Z_EROFS_VLE_DI_CLUSTER_TYPE_BITS        2
 #define Z_EROFS_VLE_DI_CLUSTER_TYPE_BIT         0
 
+/* (noncompact only, HEAD) This pcluster refers to partial decompressed data */
+#define Z_EROFS_VLE_DI_PARTIAL_REF		(1 << 15)
+
 /*
  * D0_CBLKCNT will be marked _only_ at the 1st non-head lcluster to store the
  * compressed block count of a compressed extent (in logical clusters, aka.

fs/erofs/internal.h

@@ -291,6 +291,7 @@ EROFS_FEATURE_FUNCS(device_table, incompat, INCOMPAT_DEVICE_TABLE)
 EROFS_FEATURE_FUNCS(compr_head2, incompat, INCOMPAT_COMPR_HEAD2)
 EROFS_FEATURE_FUNCS(ztailpacking, incompat, INCOMPAT_ZTAILPACKING)
 EROFS_FEATURE_FUNCS(fragments, incompat, INCOMPAT_FRAGMENTS)
+EROFS_FEATURE_FUNCS(dedupe, incompat, INCOMPAT_DEDUPE)
 EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
 
 /* atomic flag definitions */
@@ -392,6 +393,7 @@ enum {
 	BH_Encoded = BH_PrivateStart,
 	BH_FullMapped,
 	BH_Fragment,
+	BH_Partialref,
 };
 
 /* Has a disk mapping */
@@ -404,6 +406,8 @@ enum {
 #define EROFS_MAP_FULL_MAPPED	(1 << BH_FullMapped)
 /* Located in the special packed inode */
 #define EROFS_MAP_FRAGMENT	(1 << BH_Fragment)
+/* The extent refers to partial decompressed data */
+#define EROFS_MAP_PARTIAL_REF	(1 << BH_Partialref)
 
 struct erofs_map_blocks {
 	struct erofs_buf buf;

fs/erofs/super.c

@@ -424,6 +424,8 @@ static int erofs_read_superblock(struct super_block *sb)
 		erofs_info(sb, "EXPERIMENTAL fscache-based on-demand read feature in use. Use at your own risk!");
 	if (erofs_sb_has_fragments(sbi))
 		erofs_info(sb, "EXPERIMENTAL compressed fragments feature in use. Use at your own risk!");
+	if (erofs_sb_has_dedupe(sbi))
+		erofs_info(sb, "EXPERIMENTAL global deduplication feature in use. Use at your own risk!");
 out:
 	erofs_put_metabuf(&buf);
 	return ret;

fs/erofs/sysfs.c

@@ -77,6 +77,7 @@ EROFS_ATTR_FEATURE(compr_head2);
 EROFS_ATTR_FEATURE(sb_chksum);
 EROFS_ATTR_FEATURE(ztailpacking);
 EROFS_ATTR_FEATURE(fragments);
+EROFS_ATTR_FEATURE(dedupe);
 
 static struct attribute *erofs_feat_attrs[] = {
 	ATTR_LIST(zero_padding),
@@ -88,6 +89,7 @@ static struct attribute *erofs_feat_attrs[] = {
 	ATTR_LIST(sb_chksum),
 	ATTR_LIST(ztailpacking),
 	ATTR_LIST(fragments),
+	ATTR_LIST(dedupe),
 	NULL,
 };
 ATTRIBUTE_GROUPS(erofs_feat);

fs/erofs/zdata.c

@@ -814,6 +814,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
 		fe->pcl->multibases = true;
 
 	if ((map->m_flags & EROFS_MAP_FULL_MAPPED) &&
+	    !(map->m_flags & EROFS_MAP_PARTIAL_REF) &&
 	    fe->pcl->length == map->m_llen)
 		fe->pcl->partial = false;
 	if (fe->pcl->length < offset + end - map->m_la) {

fs/erofs/zmap.c

@@ -163,6 +163,7 @@ struct z_erofs_maprecorder {
 	u16 delta[2];
 	erofs_blk_t pblk, compressedblks;
 	erofs_off_t nextpackoff;
+	bool partialref;
 };
 
 static int z_erofs_reload_indexes(struct z_erofs_maprecorder *m,
@@ -221,6 +222,8 @@ static int legacy_load_cluster_from_disk(struct z_erofs_maprecorder *m,
 	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
 	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD1:
 	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD2:
+		if (advise & Z_EROFS_VLE_DI_PARTIAL_REF)
+			m->partialref = true;
 		m->clusterofs = le16_to_cpu(di->di_clusterofs);
 		m->pblk = le32_to_cpu(di->di_u.blkaddr);
 		break;
@@ -684,7 +687,8 @@ static int z_erofs_do_map_blocks(struct inode *inode,
 		err = -EOPNOTSUPP;
 		goto unmap_out;
 	}
-
+	if (m.partialref)
+		map->m_flags |= EROFS_MAP_PARTIAL_REF;
 	map->m_llen = end - map->m_la;
 
 	if (flags & EROFS_GET_BLOCKS_FINDTAIL) {