Commit 54ab25d0 authored by Gao Xiang's avatar Gao Xiang
Browse files

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: default avatarChao Yu <chao@kernel.org>
Signed-off-by: default avatarGao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20241212023948.1143038-1-hsiangkao@linux.alibaba.com
parent a78c5c22

fs/erofs/erofs_fs.h

+2 −1
Original line number Diff line number Diff line
@@ -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 */

fs/erofs/super.c

+11 −19
Original line number Diff line number Diff line
@@ -39,30 +39,22 @@ 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) {

	/* 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, expected_crc);

		  crc, le32_to_cpu(dsb->checksum));

	return -EBADMSG;

}

	return 0;

}



static void erofs_inode_init_once(void *ptr)

{