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erofs: micro-optimize superblock checksum 

Just verify the remaining unknown on-disk data instead of allocating a
temporary buffer for the whole superblock and zeroing out the checksum
field since .magic(EROFS_SUPER_MAGIC_V1) is verified and .checksum(0)
is fixed.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20241212023948.1143038-1-hsiangkao@linux.alibaba.com
This commit is contained in:
Gao Xiang 2024-12-12 10:39:48 +08:00
parent a78c5c2269
commit 54ab25d03e
2 changed files with 13 additions and 20 deletions
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3
fs/erofs/erofs_fs.h
View File

@ -9,6 +9,7 @@
#ifndef __EROFS_FS_H
#define __EROFS_FS_H
/* to allow for x86 boot sectors and other oddities. */
#define EROFS_SUPER_OFFSET 1024
#define EROFS_FEATURE_COMPAT_SB_CHKSUM 0x00000001
@ -54,7 +55,7 @@ struct erofs_deviceslot {
/* erofs on-disk super block (currently 128 bytes) */
struct erofs_super_block {
__le32 magic; /* file system magic number */
__le32 checksum; /* crc32c(super_block) */
__le32 checksum; /* crc32c to avoid unexpected on-disk overlap */
__le32 feature_compat;
__u8 blkszbits; /* filesystem block size in bit shift */
__u8 sb_extslots; /* superblock size = 128 + sb_extslots * 16 */

30
fs/erofs/super.c
View File

@ -39,29 +39,21 @@ void _erofs_printk(struct super_block *sb, const char *fmt, ...)
static int erofs_superblock_csum_verify(struct super_block *sb, void *sbdata)
{
size_t len = 1 << EROFS_SB(sb)->blkszbits;
struct erofs_super_block *dsb;
u32 expected_crc, crc;
struct erofs_super_block *dsb = sbdata + EROFS_SUPER_OFFSET;
u32 len = 1 << EROFS_SB(sb)->blkszbits, crc;
if (len > EROFS_SUPER_OFFSET)
len -= EROFS_SUPER_OFFSET;
len -= offsetof(struct erofs_super_block, checksum) +
sizeof(dsb->checksum);
dsb = kmemdup(sbdata + EROFS_SUPER_OFFSET, len, GFP_KERNEL);
if (!dsb)
return -ENOMEM;
expected_crc = le32_to_cpu(dsb->checksum);
dsb->checksum = 0;
/* to allow for x86 boot sectors and other oddities. */
crc = crc32c(~0, dsb, len);
kfree(dsb);
if (crc != expected_crc) {
erofs_err(sb, "invalid checksum 0x%08x, 0x%08x expected",
crc, expected_crc);
return -EBADMSG;
}
return 0;
/* skip .magic(pre-verified) and .checksum(0) fields */
crc = crc32c(0x5045B54A, (&dsb->checksum) + 1, len);
if (crc == le32_to_cpu(dsb->checksum))
return 0;
erofs_err(sb, "invalid checksum 0x%08x, 0x%08x expected",
crc, le32_to_cpu(dsb->checksum));
return -EBADMSG;
}
static void erofs_inode_init_once(void *ptr)