1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _XFS_CKSUM_H
3#define _XFS_CKSUM_H 1
4
5#define XFS_CRC_SEED	(~(uint32_t)0)
6
7/*
8 * Calculate the intermediate checksum for a buffer that has the CRC field
9 * inside it.  The offset of the 32bit crc fields is passed as the
10 * cksum_offset parameter. We do not modify the buffer during verification,
11 * hence we have to split the CRC calculation across the cksum_offset.
12 */
13static inline uint32_t
14xfs_start_cksum_safe(char *buffer, size_t length, unsigned long cksum_offset)
15{
16	uint32_t zero = 0;
17	uint32_t crc;
18
19	/* Calculate CRC up to the checksum. */
20	crc = crc32c(XFS_CRC_SEED, buffer, cksum_offset);
21
22	/* Skip checksum field */
23	crc = crc32c(crc, &zero, sizeof(__u32));
24
25	/* Calculate the rest of the CRC. */
26	return crc32c(crc, &buffer[cksum_offset + sizeof(__be32)],
27		      length - (cksum_offset + sizeof(__be32)));
28}
29
30/*
31 * Fast CRC method where the buffer is modified. Callers must have exclusive
32 * access to the buffer while the calculation takes place.
33 */
34static inline uint32_t
35xfs_start_cksum_update(char *buffer, size_t length, unsigned long cksum_offset)
36{
37	/* zero the CRC field */
38	*(__le32 *)(buffer + cksum_offset) = 0;
39
40	/* single pass CRC calculation for the entire buffer */
41	return crc32c(XFS_CRC_SEED, buffer, length);
42}
43
44/*
45 * Convert the intermediate checksum to the final ondisk format.
46 *
47 * The CRC32c calculation uses LE format even on BE machines, but returns the
48 * result in host endian format. Hence we need to byte swap it back to LE format
49 * so that it is consistent on disk.
50 */
51static inline __le32
52xfs_end_cksum(uint32_t crc)
53{
54	return ~cpu_to_le32(crc);
55}
56
57/*
58 * Helper to generate the checksum for a buffer.
59 *
60 * This modifies the buffer temporarily - callers must have exclusive
61 * access to the buffer while the calculation takes place.
62 */
63static inline void
64xfs_update_cksum(char *buffer, size_t length, unsigned long cksum_offset)
65{
66	uint32_t crc = xfs_start_cksum_update(buffer, length, cksum_offset);
67
68	*(__le32 *)(buffer + cksum_offset) = xfs_end_cksum(crc);
69}
70
71/*
72 * Helper to verify the checksum for a buffer.
73 */
74static inline int
75xfs_verify_cksum(char *buffer, size_t length, unsigned long cksum_offset)
76{
77	uint32_t crc = xfs_start_cksum_safe(buffer, length, cksum_offset);
78
79	return *(__le32 *)(buffer + cksum_offset) == xfs_end_cksum(crc);
80}
81
82#endif /* _XFS_CKSUM_H */
83