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