staging: erofs: tidy up decompression frontend

Although this patch has an amount of changes, it is hard to
separate into smaller patches.

Most changes are due to structure renaming for better understand
and straightforward,
 z_erofs_vle_workgroup to z_erofs_pcluster
             since it represents a physical cluster;
 z_erofs_vle_work to z_erofs_collection
             since it represents a collection of logical pages;
 z_erofs_vle_work_builder to z_erofs_collector
             since it's used to fill z_erofs_{pcluster,collection}.

struct z_erofs_vle_work_finder has no extra use compared with
struct z_erofs_collector, delete it.

FULL_LENGTH bit is integrated into .length of pcluster so that it
can be updated with the corresponding length change in atomic.

Minor, add comments for better description.
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Link: https://lore.kernel.org/r/20190731155752.210602-18-gaoxiang25@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/erofs/zdata.h

@@ -18,80 +18,77 @@
  * Structure fields follow one of the following exclusion rules.
  *
  * I: Modifiable by initialization/destruction paths and read-only
- *    for everyone else.
+ *    for everyone else;
  *
+ * L: Field should be protected by pageset lock;
+ *
+ * A: Field should be accessed / updated in atomic for parallelized code.
  */
-
-struct z_erofs_vle_work {
+struct z_erofs_collection {
 	struct mutex lock;
 
-	/* I: decompression offset in page */
+	/* I: page offset of start position of decompression */
 	unsigned short pageofs;
+
+	/* L: maximum relative page index in pagevec[] */
 	unsigned short nr_pages;
 
-	/* L: queued pages in pagevec[] */
+	/* L: total number of pages in pagevec[] */
 	unsigned int vcnt;
 
 	union {
-		/* L: pagevec */
+		/* L: inline a certain number of pagevecs for bootstrap */
 		erofs_vtptr_t pagevec[Z_EROFS_NR_INLINE_PAGEVECS];
+
+		/* I: can be used to free the pcluster by RCU. */
 		struct rcu_head rcu;
 	};
 };
 
-#define Z_EROFS_VLE_WORKGRP_FMT_PLAIN        0
-#define Z_EROFS_VLE_WORKGRP_FMT_LZ4          1
-#define Z_EROFS_VLE_WORKGRP_FMT_MASK         1
-#define Z_EROFS_VLE_WORKGRP_FULL_LENGTH      2
+#define Z_EROFS_PCLUSTER_FULL_LENGTH    0x00000001
+#define Z_EROFS_PCLUSTER_LENGTH_BIT     1
 
-typedef void *z_erofs_vle_owned_workgrp_t;
+/*
+ * let's leave a type here in case of introducing
+ * another tagged pointer later.
+ */
+typedef void *z_erofs_next_pcluster_t;
 
-struct z_erofs_vle_workgroup {
+struct z_erofs_pcluster {
 	struct erofs_workgroup obj;
-	struct z_erofs_vle_work work;
+	struct z_erofs_collection primary_collection;
 
-	/* point to next owned_workgrp_t */
-	z_erofs_vle_owned_workgrp_t next;
+	/* A: point to next chained pcluster or TAILs */
+	z_erofs_next_pcluster_t next;
 
-	/* compressed pages (including multi-usage pages) */
+	/* A: compressed pages (including multi-usage pages) */
 	struct page *compressed_pages[Z_EROFS_CLUSTER_MAX_PAGES];
-	unsigned int llen, flags;
+
+	/* A: lower limit of decompressed length and if full length or not */
+	unsigned int length;
+
+	/* I: compression algorithm format */
+	unsigned char algorithmformat;
+	/* I: bit shift of physical cluster size */
+	unsigned char clusterbits;
 };
 
+#define z_erofs_primarycollection(pcluster) (&(pcluster)->primary_collection)
+
 /* let's avoid the valid 32-bit kernel addresses */
 
 /* the chained workgroup has't submitted io (still open) */
-#define Z_EROFS_VLE_WORKGRP_TAIL        ((void *)0x5F0ECAFE)
+#define Z_EROFS_PCLUSTER_TAIL           ((void *)0x5F0ECAFE)
 /* the chained workgroup has already submitted io */
-#define Z_EROFS_VLE_WORKGRP_TAIL_CLOSED ((void *)0x5F0EDEAD)
+#define Z_EROFS_PCLUSTER_TAIL_CLOSED    ((void *)0x5F0EDEAD)
 
-#define Z_EROFS_VLE_WORKGRP_NIL         (NULL)
+#define Z_EROFS_PCLUSTER_NIL            (NULL)
 
-#define z_erofs_vle_workgrp_fmt(grp)	\
-	((grp)->flags & Z_EROFS_VLE_WORKGRP_FMT_MASK)
+#define Z_EROFS_WORKGROUP_SIZE  sizeof(struct z_erofs_pcluster)
 
-static inline void z_erofs_vle_set_workgrp_fmt(
-	struct z_erofs_vle_workgroup *grp,
-	unsigned int fmt)
-{
-	grp->flags = fmt | (grp->flags & ~Z_EROFS_VLE_WORKGRP_FMT_MASK);
-}
-
-
-/* definitions if multiref is disabled */
-#define z_erofs_vle_grab_primary_work(grp)	(&(grp)->work)
-#define z_erofs_vle_grab_work(grp, pageofs)	(&(grp)->work)
-#define z_erofs_vle_work_workgroup(wrk, primary)	\
-	((primary) ? container_of(wrk,	\
-		struct z_erofs_vle_workgroup, work) : \
-		({ BUG(); (void *)NULL; }))
-
-
-#define Z_EROFS_WORKGROUP_SIZE       sizeof(struct z_erofs_vle_workgroup)
-
-struct z_erofs_vle_unzip_io {
+struct z_erofs_unzip_io {
 	atomic_t pending_bios;
-	z_erofs_vle_owned_workgrp_t head;
+	z_erofs_next_pcluster_t head;
 
 	union {
 		wait_queue_head_t wait;
@@ -99,8 +96,8 @@ struct z_erofs_vle_unzip_io {
 	} u;
 };
 
-struct z_erofs_vle_unzip_io_sb {
-	struct z_erofs_vle_unzip_io io;
+struct z_erofs_unzip_io_sb {
+	struct z_erofs_unzip_io io;
 	struct super_block *sb;
 };
 
@@ -193,13 +190,12 @@ static inline void z_erofs_onlinepage_endio(struct page *page)
 			SetPageUptodate(page);
 		unlock_page(page);
 	}
-
 	debugln("%s, page %p value %x", __func__, page, atomic_read(u.o));
 }
 
-#define Z_EROFS_VLE_VMAP_ONSTACK_PAGES	\
+#define Z_EROFS_VMAP_ONSTACK_PAGES	\
 	min_t(unsigned int, THREAD_SIZE / 8 / sizeof(struct page *), 96U)
-#define Z_EROFS_VLE_VMAP_GLOBAL_PAGES	2048
+#define Z_EROFS_VMAP_GLOBAL_PAGES	2048
 
 #endif