diff options
Diffstat (limited to 'fs/xfs/libxfs/xfs_cksum.h')
| -rw-r--r-- | fs/xfs/libxfs/xfs_cksum.h | 26 |
1 files changed, 22 insertions, 4 deletions
diff --git a/fs/xfs/libxfs/xfs_cksum.h b/fs/xfs/libxfs/xfs_cksum.h index fad1676ad8cd..a416c7cb23ea 100644 --- a/fs/xfs/libxfs/xfs_cksum.h +++ b/fs/xfs/libxfs/xfs_cksum.h @@ -6,10 +6,11 @@ /* * Calculate the intermediate checksum for a buffer that has the CRC field * inside it. The offset of the 32bit crc fields is passed as the - * cksum_offset parameter. + * cksum_offset parameter. We do not modify the buffer during verification, + * hence we have to split the CRC calculation across the cksum_offset. */ static inline __uint32_t -xfs_start_cksum(char *buffer, size_t length, unsigned long cksum_offset) +xfs_start_cksum_safe(char *buffer, size_t length, unsigned long cksum_offset) { __uint32_t zero = 0; __uint32_t crc; @@ -26,6 +27,20 @@ xfs_start_cksum(char *buffer, size_t length, unsigned long cksum_offset) } /* + * Fast CRC method where the buffer is modified. Callers must have exclusive + * access to the buffer while the calculation takes place. + */ +static inline __uint32_t +xfs_start_cksum_update(char *buffer, size_t length, unsigned long cksum_offset) +{ + /* zero the CRC field */ + *(__le32 *)(buffer + cksum_offset) = 0; + + /* single pass CRC calculation for the entire buffer */ + return crc32c(XFS_CRC_SEED, buffer, length); +} + +/* * Convert the intermediate checksum to the final ondisk format. * * The CRC32c calculation uses LE format even on BE machines, but returns the @@ -40,11 +55,14 @@ xfs_end_cksum(__uint32_t crc) /* * Helper to generate the checksum for a buffer. + * + * This modifies the buffer temporarily - callers must have exclusive + * access to the buffer while the calculation takes place. */ static inline void xfs_update_cksum(char *buffer, size_t length, unsigned long cksum_offset) { - __uint32_t crc = xfs_start_cksum(buffer, length, cksum_offset); + __uint32_t crc = xfs_start_cksum_update(buffer, length, cksum_offset); *(__le32 *)(buffer + cksum_offset) = xfs_end_cksum(crc); } @@ -55,7 +73,7 @@ xfs_update_cksum(char *buffer, size_t length, unsigned long cksum_offset) static inline int xfs_verify_cksum(char *buffer, size_t length, unsigned long cksum_offset) { - __uint32_t crc = xfs_start_cksum(buffer, length, cksum_offset); + __uint32_t crc = xfs_start_cksum_safe(buffer, length, cksum_offset); return *(__le32 *)(buffer + cksum_offset) == xfs_end_cksum(crc); } |