xfs/libxfs/xfs_cksum.h

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002 #ifndef _XFS_CKSUM_H
0003 #define _XFS_CKSUM_H 1
0004
0005 #define XFS_CRC_SEED    (~(uint32_t)0)
0006
0007 /*
0008  * Calculate the intermediate checksum for a buffer that has the CRC field
0009  * inside it.  The offset of the 32bit crc fields is passed as the
0010  * cksum_offset parameter. We do not modify the buffer during verification,
0011  * hence we have to split the CRC calculation across the cksum_offset.
0012  */
0013 static inline uint32_t
0014 xfs_start_cksum_safe(char *buffer, size_t length, unsigned long cksum_offset)
0015 {
0016     uint32_t zero = 0;
0017     uint32_t crc;
0018
0019     /* Calculate CRC up to the checksum. */
0020     crc = crc32c(XFS_CRC_SEED, buffer, cksum_offset);
0021
0022     /* Skip checksum field */
0023     crc = crc32c(crc, &zero, sizeof(__u32));
0024
0025     /* Calculate the rest of the CRC. */
0026     return crc32c(crc, &buffer[cksum_offset + sizeof(__be32)],
0027               length - (cksum_offset + sizeof(__be32)));
0028 }
0029
0030 /*
0031  * Fast CRC method where the buffer is modified. Callers must have exclusive
0032  * access to the buffer while the calculation takes place.
0033  */
0034 static inline uint32_t
0035 xfs_start_cksum_update(char *buffer, size_t length, unsigned long cksum_offset)
0036 {
0037     /* zero the CRC field */
0038     *(__le32 *)(buffer + cksum_offset) = 0;
0039
0040     /* single pass CRC calculation for the entire buffer */
0041     return crc32c(XFS_CRC_SEED, buffer, length);
0042 }
0043
0044 /*
0045  * Convert the intermediate checksum to the final ondisk format.
0046  *
0047  * The CRC32c calculation uses LE format even on BE machines, but returns the
0048  * result in host endian format. Hence we need to byte swap it back to LE format
0049  * so that it is consistent on disk.
0050  */
0051 static inline __le32
0052 xfs_end_cksum(uint32_t crc)
0053 {
0054     return ~cpu_to_le32(crc);
0055 }
0056
0057 /*
0058  * Helper to generate the checksum for a buffer.
0059  *
0060  * This modifies the buffer temporarily - callers must have exclusive
0061  * access to the buffer while the calculation takes place.
0062  */
0063 static inline void
0064 xfs_update_cksum(char *buffer, size_t length, unsigned long cksum_offset)
0065 {
0066     uint32_t crc = xfs_start_cksum_update(buffer, length, cksum_offset);
0067
0068     *(__le32 *)(buffer + cksum_offset) = xfs_end_cksum(crc);
0069 }
0070
0071 /*
0072  * Helper to verify the checksum for a buffer.
0073  */
0074 static inline int
0075 xfs_verify_cksum(char *buffer, size_t length, unsigned long cksum_offset)
0076 {
0077     uint32_t crc = xfs_start_cksum_safe(buffer, length, cksum_offset);
0078
0079     return *(__le32 *)(buffer + cksum_offset) == xfs_end_cksum(crc);
0080 }
0081
0082 #endif /* _XFS_CKSUM_H */