tar_chksm
blck = tar_chksm(bl, bllen);
if (u32_oct(tar_chksm(hdblk, sizeof(HD_USTAR)), hd->chksum,
if (u32_oct(tar_chksm(hdblk, sizeof(HD_TAR)), hd->chksum,
static uint32_t tar_chksm(char *, int);