fs/xfs/libxfs/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. We do not modify the buffer during verification,
  10  * hence we have to split the CRC calculation across the cksum_offset.
  11  */
  12 static inline uint32_t
  13 xfs_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  */
  33 static inline uint32_t
  34 xfs_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  */
  50 static inline __le32
  51 xfs_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  */
  62 static inline void
  63 xfs_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  */
  73 static inline int
  74 xfs_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 */