LXR linux/fs/xfs/libxfs/xfs

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