_CMSG_HDR_ALIGNMENT
char cinmsg[sizeof (*sinfo) + sizeof (*cmsg) + _CMSG_HDR_ALIGNMENT];
char coutmsg[sizeof (*sinfo) + sizeof (*cmsg) + _CMSG_HDR_ALIGNMENT];
#define _CMSG_HDR_ALIGN(x) (((uintptr_t)(x) + _CMSG_HDR_ALIGNMENT - 1) & \
~(_CMSG_HDR_ALIGNMENT - 1))
#define _CMSG_HDR_ALIGN(x) (((uintptr_t)(x) + _CMSG_HDR_ALIGNMENT - 1) & \
~(_CMSG_HDR_ALIGNMENT - 1))
(((uintptr_t)(addr) & (_CMSG_HDR_ALIGNMENT - 1)) == 0)
(((len) + _CMSG_HDR_ALIGNMENT - 1) & ~(_CMSG_HDR_ALIGNMENT - 1))