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