LH_V1_SIZE
hash = ~crc32(~0, lh, LH_V1_SIZE);
BUILD_BUG_ON(offsetof(struct gfs2_log_header, lh_crc) != LH_V1_SIZE);
crc = crc32c(~0, (void *)lh + LH_V1_SIZE + 4,
sb->s_blocksize - LH_V1_SIZE - 4);
hash = crc32(~0, lh, LH_V1_SIZE - 4);
crc = crc32c(~0, (void *)lh + LH_V1_SIZE + 4,
sdp->sd_sb.sb_bsize - LH_V1_SIZE - 4);