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
xfs_start_cksum_safe(char * buffer,size_t length,unsigned long cksum_offset)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
xfs_start_cksum_update(char * buffer,size_t length,unsigned long cksum_offset)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
xfs_end_cksum(uint32_t crc)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
xfs_update_cksum(char * buffer,size_t length,unsigned long cksum_offset)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
xfs_verify_cksum(char * buffer,size_t length,unsigned long cksum_offset)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