[PATCH] erofs-utils: lib: fix sub-page block handling in erofs_read_superblock()

[Gao Xiang]

`sbi->sb_size > (1 << sbi->blkszbits) - EROFS_SUPER_OFFSET ` doesn't
work correctly when the block size is 1024.

Signed-off-by: Gao Xiang <hsiang...@linux.alibaba.com>
---
 lib/super.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/lib/super.c b/lib/super.c
index fb644bc..8efef50 100644
--- a/lib/super.c
+++ b/lib/super.c
@@ -76,13 +76,13 @@ int erofs_read_superblock(struct erofs_sb_info *sbi)
 {
        u8 data[EROFS_MAX_BLOCK_SIZE];
        struct erofs_super_block *dsb;
-       int ret;
+       int read, ret;
 
-       sbi->blkszbits = ilog2(EROFS_MAX_BLOCK_SIZE);
-       ret = erofs_blk_read(sbi, 0, data, 0, erofs_blknr(sbi, sizeof(data)));
-       if (ret < 0) {
+       read = erofs_io_pread(&sbi->bdev, data, 0, EROFS_MAX_BLOCK_SIZE);
+       if (read < EROFS_SUPER_END) {
+               ret = read < 0 ? read : -EIO;
                erofs_err("cannot read erofs superblock: %d", ret);
-               return -EIO;
+               return ret;
        }
        dsb = (struct erofs_super_block *)(data + EROFS_SUPER_OFFSET);
 
@@ -105,9 +105,8 @@ int erofs_read_superblock(struct erofs_sb_info *sbi)
        }
 
        sbi->sb_size = 128 + dsb->sb_extslots * EROFS_SB_EXTSLOT_SIZE;
-       if (sbi->sb_size > (1 << sbi->blkszbits) - EROFS_SUPER_OFFSET) {
-               erofs_err("invalid sb_extslots %u (more than a fs block)",
-                         dsb->sb_extslots);
+       if (sbi->sb_size > read - EROFS_SUPER_OFFSET) {
+               erofs_err("invalid sb_extslots %u", dsb->sb_extslots);
                return -EINVAL;
        }
        sbi->primarydevice_blocks = le32_to_cpu(dsb->blocks_lo);
-- 
2.43.5