LXR linux/fs/xfs/libxfs/xfs

   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. We do not modify the buffer during verification,
  10 * hence we have to split the CRC calculation across the cksum_offset.
  11 */
  12static inline __uint32_t
  13xfs_start_cksum_safe(char *buffer, size_t length, unsigned long cksum_offset)
  14{
  15        __uint32_t zero = 0;
  16        __uint32_t crc;
  17
  18        /* Calculate CRC up to the checksum. */
  19        crc = crc32c(XFS_CRC_SEED, buffer, cksum_offset);
  20
  21        /* Skip checksum field */
  22        crc = crc32c(crc, &zero, sizeof(__u32));
  23
  24        /* Calculate the rest of the CRC. */
  25        return crc32c(crc, &buffer[cksum_offset + sizeof(__be32)],
  26                      length - (cksum_offset + sizeof(__be32)));
  27}
  28
  29/*
  30 * Fast CRC method where the buffer is modified. Callers must have exclusive
  31 * access to the buffer while the calculation takes place.
  32 */
  33static inline __uint32_t
  34xfs_start_cksum_update(char *buffer, size_t length, unsigned long cksum_offset)
  35{
  36        /* zero the CRC field */
  37        *(__le32 *)(buffer + cksum_offset) = 0;
  38
  39        /* single pass CRC calculation for the entire buffer */
  40        return crc32c(XFS_CRC_SEED, buffer, length);
  41}
  42
  43/*
  44 * Convert the intermediate checksum to the final ondisk format.
  45 *
  46 * The CRC32c calculation uses LE format even on BE machines, but returns the
  47 * result in host endian format. Hence we need to byte swap it back to LE format
  48 * so that it is consistent on disk.
  49 */
  50static inline __le32
  51xfs_end_cksum(__uint32_t crc)
  52{
  53        return ~cpu_to_le32(crc);
  54}
  55
  56/*
  57 * Helper to generate the checksum for a buffer.
  58 *
  59 * This modifies the buffer temporarily - callers must have exclusive
  60 * access to the buffer while the calculation takes place.
  61 */
  62static inline void
  63xfs_update_cksum(char *buffer, size_t length, unsigned long cksum_offset)
  64{
  65        __uint32_t crc = xfs_start_cksum_update(buffer, length, cksum_offset);
  66
  67        *(__le32 *)(buffer + cksum_offset) = xfs_end_cksum(crc);
  68}
  69
  70/*
  71 * Helper to verify the checksum for a buffer.
  72 */
  73static inline int
  74xfs_verify_cksum(char *buffer, size_t length, unsigned long cksum_offset)
  75{
  76        __uint32_t crc = xfs_start_cksum_safe(buffer, length, cksum_offset);
  77
  78        return *(__le32 *)(buffer + cksum_offset) == xfs_end_cksum(crc);
  79}
  80
  81#endif /* _XFS_CKSUM_H */
  82