f2fs: describe SIT block layout dynamically

An SIT block consists of an on-disk array of struct f2fs_sit_entry elements
whose total capacity depends on the filesystem block size. The existing
fixed SIT_ENTRY_PER_BLOCK macro hardcodes a 4KB block size.

Convert the entries array in struct f2fs_sit_block into a C flexible array
member, and calculate sbi->sit_entries_per_block dynamically in
init_sb_info().

Parameterize SIT indexing helpers (SIT_ENTRY_PER_BLOCK, SIT_BLOCK_OFFSET,
SIT_BLK_CNT, and f2fs_start_segno) to take struct f2fs_sb_info *sbi, and
update all call sites across segment management, checkpointing, and mount.

This is a layout-only change; valid 4KB filesystems retain identical
runtime geometry and behavior.

Signed-off-by: Kelvin Zhang <zhangxp1998@gmail.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h
index bb2b6cd5d507..ecd6694af572 100644
--- a/include/linux/f2fs_fs.h
+++ b/include/linux/f2fs_fs.h
@@ -396,8 +396,6 @@ struct f2fs_nat_block {
  * Not allow to change this.
  */
 #define SIT_VBLOCK_MAP_SIZE 64
-#define SIT_ENTRY_PER_BLOCK (F2FS_BLKSIZE / sizeof(struct f2fs_sit_entry))
-
 /*
  * F2FS uses 4 bytes to represent block address. As a result, supported size of
  * disk is 16 TB for a 4K page size and 64 TB for a 16K page size and it equals
@@ -424,8 +422,13 @@ struct f2fs_sit_entry {
 	__le64 mtime;				/* segment age for cleaning */
 } __packed;
 
+/*
+ * The on-disk SIT block is a filesystem-block-sized array of SIT entries.
+ * Its entry count depends on the filesystem block size, so it must be
+ * calculated by the caller rather than implied by this C structure.
+ */
 struct f2fs_sit_block {
-	struct f2fs_sit_entry entries[SIT_ENTRY_PER_BLOCK];
+	DECLARE_FLEX_ARRAY(struct f2fs_sit_entry, entries);
 } __packed;
 
 /*