erofs: add big physical cluster definition

Big pcluster indicates the size of compressed data for each physical
pcluster is no longer fixed as block size, but could be more than 1
block (more accurately, 1 logical pcluster)

When big pcluster feature is enabled for head0/1, delta0 of the 1st
non-head lcluster index will keep block count of this pcluster in
lcluster size instead of 1. Or, the compressed size of pcluster
should be 1 lcluster if pcluster has no non-head lcluster index.

Also note that BIG_PCLUSTER feature reuses COMPR_CFGS feature since
it depends on COMPR_CFGS and will be released together.

Link: https://lore.kernel.org/r/20210407043927.10623-6-xiang@kernel.org
Acked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

fs/erofs/erofs_fs.h

@@ -19,6 +19,7 @@
  */
 #define EROFS_FEATURE_INCOMPAT_LZ4_0PADDING	0x00000001
 #define EROFS_FEATURE_INCOMPAT_COMPR_CFGS	0x00000002
+#define EROFS_FEATURE_INCOMPAT_BIG_PCLUSTER	0x00000002
 #define EROFS_ALL_FEATURE_INCOMPAT		EROFS_FEATURE_INCOMPAT_LZ4_0PADDING
 
 #define EROFS_SB_EXTSLOT_SIZE	16
@@ -214,17 +215,20 @@ enum {
 /* 14 bytes (+ length field = 16 bytes) */
 struct z_erofs_lz4_cfgs {
 	__le16 max_distance;
-	u8 reserved[12];
+	__le16 max_pclusterblks;
+	u8 reserved[10];
 } __packed;
 
 /*
  * bit 0 : COMPACTED_2B indexes (0 - off; 1 - on)
  *  e.g. for 4k logical cluster size,      4B        if compacted 2B is off;
  *                                  (4B) + 2B + (4B) if compacted 2B is on.
+ * bit 1 : HEAD1 big pcluster (0 - off; 1 - on)
+ * bit 2 : HEAD2 big pcluster (0 - off; 1 - on)
  */
-#define Z_EROFS_ADVISE_COMPACTED_2B_BIT         0
-
-#define Z_EROFS_ADVISE_COMPACTED_2B     (1 << Z_EROFS_ADVISE_COMPACTED_2B_BIT)
+#define Z_EROFS_ADVISE_COMPACTED_2B		0x0001
+#define Z_EROFS_ADVISE_BIG_PCLUSTER_1		0x0002
+#define Z_EROFS_ADVISE_BIG_PCLUSTER_2		0x0004
 
 struct z_erofs_map_header {
 	__le32	h_reserved1;
@@ -279,6 +283,13 @@ enum {
 #define Z_EROFS_VLE_DI_CLUSTER_TYPE_BITS        2
 #define Z_EROFS_VLE_DI_CLUSTER_TYPE_BIT         0
 
+/*
+ * 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.
+ * block count of a pcluster).
+ */
+#define Z_EROFS_VLE_DI_D0_CBLKCNT		(1 << 11)
+
 struct z_erofs_vle_decompressed_index {
 	__le16 di_advise;
 	/* where to decompress in the head cluster */

fs/erofs/internal.h

@@ -230,6 +230,7 @@ static inline bool erofs_sb_has_##name(struct erofs_sb_info *sbi) \
 
 EROFS_FEATURE_FUNCS(lz4_0padding, incompat, INCOMPAT_LZ4_0PADDING)
 EROFS_FEATURE_FUNCS(compr_cfgs, incompat, INCOMPAT_COMPR_CFGS)
+EROFS_FEATURE_FUNCS(big_pcluster, incompat, INCOMPAT_BIG_PCLUSTER)
 EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
 
 /* atomic flag definitions */