linux/fs/xfs/xfs_cksum.h
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   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.
  10 */
  11static inline __uint32_t
  12xfs_start_cksum(char *buffer, size_t length, unsigned long cksum_offset)
  13{
  14        __uint32_t zero = 0;
  15        __uint32_t crc;
  16
  17        /* Calculate CRC up to the checksum. */
  18        crc = crc32c(XFS_CRC_SEED, buffer, cksum_offset);
  19
  20        /* Skip checksum field */
  21        crc = crc32c(crc, &zero, sizeof(__u32));
  22
  23        /* Calculate the rest of the CRC. */
  24        return crc32c(crc, &buffer[cksum_offset + sizeof(__be32)],
  25                      length - (cksum_offset + sizeof(__be32)));
  26}
  27
  28/*
  29 * Convert the intermediate checksum to the final ondisk format.
  30 *
  31 * The CRC32c calculation uses LE format even on BE machines, but returns the
  32 * result in host endian format. Hence we need to byte swap it back to LE format
  33 * so that it is consistent on disk.
  34 */
  35static inline __le32
  36xfs_end_cksum(__uint32_t crc)
  37{
  38        return ~cpu_to_le32(crc);
  39}
  40
  41/*
  42 * Helper to generate the checksum for a buffer.
  43 */
  44static inline void
  45xfs_update_cksum(char *buffer, size_t length, unsigned long cksum_offset)
  46{
  47        __uint32_t crc = xfs_start_cksum(buffer, length, cksum_offset);
  48
  49        *(__le32 *)(buffer + cksum_offset) = xfs_end_cksum(crc);
  50}
  51
  52/*
  53 * Helper to verify the checksum for a buffer.
  54 */
  55static inline int
  56xfs_verify_cksum(char *buffer, size_t length, unsigned long cksum_offset)
  57{
  58        __uint32_t crc = xfs_start_cksum(buffer, length, cksum_offset);
  59
  60        return *(__le32 *)(buffer + cksum_offset) == xfs_end_cksum(crc);
  61}
  62
  63#endif /* _XFS_CKSUM_H */
  64
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