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 */
13 static inline uint32_t
14 xfs_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 */
34 static inline uint32_t
35 xfs_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 */
51 static inline __le32
52 xfs_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 */
63 static inline void
64 xfs_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 */
74 static inline int
75 xfs_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
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