Commit 8805dbcb authored by Eric Biggers's avatar Eric Biggers Committed by Theodore Ts'o
Browse files

ext4: simplify fast-commit CRC calculation 



Instead of checksumming each field as it is added to the block, just
checksum each block before it is written.  This is simpler, and also
much more efficient.

Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221106224841.279231-8-ebiggers@kernel.org


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 48a6a66d

fs/ext4/fast_commit.c

+16 −38
Original line number Diff line number Diff line
@@ -675,27 +675,6 @@ static void ext4_fc_submit_bh(struct super_block *sb, bool is_tail) 


/* Ext4 commit path routines */



/* memcpy to fc reserved space and update CRC */

static void *ext4_fc_memcpy(struct super_block *sb, void *dst, const void *src,

				int len, u32 *crc)

{

	if (crc)

		*crc = ext4_chksum(EXT4_SB(sb), *crc, src, len);

	return memcpy(dst, src, len);

}



/* memzero and update CRC */

static void *ext4_fc_memzero(struct super_block *sb, void *dst, int len,

				u32 *crc)

{

	void *ret;



	ret = memset(dst, 0, len);

	if (crc)

		*crc = ext4_chksum(EXT4_SB(sb), *crc, dst, len);

	return ret;

}



/*

 * Allocate len bytes on a fast commit buffer.

 *
@@ -749,8 +728,9 @@ static u8 *ext4_fc_reserve_space(struct super_block *sb, int len, u32 *crc) 


	tl.fc_tag = cpu_to_le16(EXT4_FC_TAG_PAD);

	tl.fc_len = cpu_to_le16(remaining);

	ext4_fc_memcpy(sb, dst, &tl, EXT4_FC_TAG_BASE_LEN, crc);

	ext4_fc_memzero(sb, dst + EXT4_FC_TAG_BASE_LEN, remaining, crc);

	memcpy(dst, &tl, EXT4_FC_TAG_BASE_LEN);

	memset(dst + EXT4_FC_TAG_BASE_LEN, 0, remaining);

	*crc = ext4_chksum(sbi, *crc, sbi->s_fc_bh->b_data, bsize);



	ext4_fc_submit_bh(sb, false);
@@ -792,13 +772,15 @@ static int ext4_fc_write_tail(struct super_block *sb, u32 crc) 
	tl.fc_len = cpu_to_le16(bsize - off + sizeof(struct ext4_fc_tail));

	sbi->s_fc_bytes = round_up(sbi->s_fc_bytes, bsize);



	ext4_fc_memcpy(sb, dst, &tl, EXT4_FC_TAG_BASE_LEN, &crc);

	memcpy(dst, &tl, EXT4_FC_TAG_BASE_LEN);

	dst += EXT4_FC_TAG_BASE_LEN;

	tail.fc_tid = cpu_to_le32(sbi->s_journal->j_running_transaction->t_tid);

	ext4_fc_memcpy(sb, dst, &tail.fc_tid, sizeof(tail.fc_tid), &crc);

	memcpy(dst, &tail.fc_tid, sizeof(tail.fc_tid));

	dst += sizeof(tail.fc_tid);

	crc = ext4_chksum(sbi, crc, sbi->s_fc_bh->b_data,

			  dst - (u8 *)sbi->s_fc_bh->b_data);

	tail.fc_crc = cpu_to_le32(crc);

	ext4_fc_memcpy(sb, dst, &tail.fc_crc, sizeof(tail.fc_crc), NULL);

	memcpy(dst, &tail.fc_crc, sizeof(tail.fc_crc));

	dst += sizeof(tail.fc_crc);

	memset(dst, 0, bsize - off); /* Don't leak uninitialized memory. */
@@ -824,8 +806,8 @@ static bool ext4_fc_add_tlv(struct super_block *sb, u16 tag, u16 len, u8 *val, 
	tl.fc_tag = cpu_to_le16(tag);

	tl.fc_len = cpu_to_le16(len);



	ext4_fc_memcpy(sb, dst, &tl, EXT4_FC_TAG_BASE_LEN, crc);

	ext4_fc_memcpy(sb, dst + EXT4_FC_TAG_BASE_LEN, val, len, crc);

	memcpy(dst, &tl, EXT4_FC_TAG_BASE_LEN);

	memcpy(dst + EXT4_FC_TAG_BASE_LEN, val, len);



	return true;

}
@@ -847,11 +829,11 @@ static bool ext4_fc_add_dentry_tlv(struct super_block *sb, u32 *crc, 
	fcd.fc_ino = cpu_to_le32(fc_dentry->fcd_ino);

	tl.fc_tag = cpu_to_le16(fc_dentry->fcd_op);

	tl.fc_len = cpu_to_le16(sizeof(fcd) + dlen);

	ext4_fc_memcpy(sb, dst, &tl, EXT4_FC_TAG_BASE_LEN, crc);

	memcpy(dst, &tl, EXT4_FC_TAG_BASE_LEN);

	dst += EXT4_FC_TAG_BASE_LEN;

	ext4_fc_memcpy(sb, dst, &fcd, sizeof(fcd), crc);

	memcpy(dst, &fcd, sizeof(fcd));

	dst += sizeof(fcd);

	ext4_fc_memcpy(sb, dst, fc_dentry->fcd_name.name, dlen, crc);

	memcpy(dst, fc_dentry->fcd_name.name, dlen);



	return true;

}
@@ -889,15 +871,11 @@ static int ext4_fc_write_inode(struct inode *inode, u32 *crc) 
	if (!dst)

		goto err;



	if (!ext4_fc_memcpy(inode->i_sb, dst, &tl, EXT4_FC_TAG_BASE_LEN, crc))

		goto err;

	memcpy(dst, &tl, EXT4_FC_TAG_BASE_LEN);

	dst += EXT4_FC_TAG_BASE_LEN;

	if (!ext4_fc_memcpy(inode->i_sb, dst, &fc_inode, sizeof(fc_inode), crc))

		goto err;

	memcpy(dst, &fc_inode, sizeof(fc_inode));

	dst += sizeof(fc_inode);

	if (!ext4_fc_memcpy(inode->i_sb, dst, (u8 *)ext4_raw_inode(&iloc),

					inode_len, crc))

		goto err;

	memcpy(dst, (u8 *)ext4_raw_inode(&iloc), inode_len);

	ret = 0;

err:

	brelse(iloc.bh);