fs/xfs/xfs_cksum.h

   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  */
  11 static inline __uint32_t
  12 xfs_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  */
  35 static inline __le32
  36 xfs_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  */
  44 static inline void
  45 xfs_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  */
  55 static inline int
  56 xfs_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 */