[PATCH 3/4] erofs: introduce on-disk lz4 fs configurations

[Gao Xiang via Linux-erofs]

From: Gao Xiang <hsiang...@redhat.com>

Introduce z_erofs_lz4_cfgs to store all lz4 configurations.
Currently it's only max_distance, but will be used for new
features later.

Signed-off-by: Gao Xiang <hsiang...@redhat.com>
---
 fs/erofs/decompressor.c | 15 +++++++++++++--
 fs/erofs/erofs_fs.h     |  6 ++++++
 fs/erofs/internal.h     |  8 +++++---
 fs/erofs/super.c        |  2 +-
 4 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
index 93411e9df9b6..97538ff24a19 100644
--- a/fs/erofs/decompressor.c
+++ b/fs/erofs/decompressor.c
@@ -29,9 +29,20 @@ struct z_erofs_decompressor {
 };
 
 int z_erofs_load_lz4_config(struct super_block *sb,
-                           struct erofs_super_block *dsb)
+                           struct erofs_super_block *dsb,
+                           struct z_erofs_lz4_cfgs *lz4, int size)
 {
-       u16 distance = le16_to_cpu(dsb->lz4_max_distance);
+       u16 distance;
+
+       if (lz4) {
+               if (size < sizeof(struct z_erofs_lz4_cfgs)) {
+                       erofs_err(sb, "invalid lz4 cfgs, size=%u", size);
+                       return -EINVAL;
+               }
+               distance = le16_to_cpu(lz4->max_distance);
+       } else {
+               distance = le16_to_cpu(dsb->lz4_max_distance);
+       }
 
        EROFS_SB(sb)->lz4.max_distance_pages = distance ?
                                        DIV_ROUND_UP(distance, PAGE_SIZE) + 1 :
diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
index b27d0e4e4ab5..1322ae63944b 100644
--- a/fs/erofs/erofs_fs.h
+++ b/fs/erofs/erofs_fs.h
@@ -196,6 +196,12 @@ enum {
        Z_EROFS_COMPRESSION_MAX
 };
 
+/* 14 bytes (+ length field = 16 bytes) */
+struct z_erofs_lz4_cfgs {
+       __le16 max_distance;
+       u8 reserved[12];
+} __packed;
+
 /*
  * bit 0 : COMPACTED_2B indexes (0 - off; 1 - on)
  *  e.g. for 4k logical cluster size,      4B        if compacted 2B is off;
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 1de60992c3dd..46b977f348eb 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -441,7 +441,8 @@ int erofs_try_to_free_all_cached_pages(struct erofs_sb_info 
*sbi,
 int erofs_try_to_free_cached_page(struct address_space *mapping,
                                  struct page *page);
 int z_erofs_load_lz4_config(struct super_block *sb,
-                           struct erofs_super_block *dsb);
+                           struct erofs_super_block *dsb,
+                           struct z_erofs_lz4_cfgs *lz4, int len);
 #else
 static inline void erofs_shrinker_register(struct super_block *sb) {}
 static inline void erofs_shrinker_unregister(struct super_block *sb) {}
@@ -450,9 +451,10 @@ static inline void erofs_exit_shrinker(void) {}
 static inline int z_erofs_init_zip_subsystem(void) { return 0; }
 static inline void z_erofs_exit_zip_subsystem(void) {}
 static inline int z_erofs_load_lz4_config(struct super_block *sb,
-                               struct erofs_super_block *dsb)
+                                 struct erofs_super_block *dsb,
+                                 struct z_erofs_lz4_cfgs *lz4, int len)
 {
-       if (dsb->lz4_max_distance) {
+       if (lz4 || dsb->lz4_max_distance) {
                erofs_err(sb, "lz4 algorithm isn't enabled");
                return -EINVAL;
        }
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 3212e4f73f85..1ca8da3f2125 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -189,7 +189,7 @@ static int erofs_read_superblock(struct super_block *sb)
        }
 
        /* parse on-disk compression configurations */
-       ret = z_erofs_load_lz4_config(sb, dsb);
+       ret = z_erofs_load_lz4_config(sb, dsb, NULL, 0);
 out:
        kunmap(page);
        put_page(page);
-- 
2.20.1