.\" This man page is Copyright (C) 1999 Andi Kleen <ak@muc.de>.
.\" Permission is granted to distribute possibly modified copies
.\" of this page provided the header is included verbatim,
.\" and in case of nontrivial modification author and date
.\" of the modification is added to the header.
.\" $Id: cmsg.3,v 1.3 2001/01/14 05:30:39 hanataka Exp $
.\"
.\" Japanese Version Copyright (c) 1999 Shouichi Saito
.\"	all rights reserved.
.\" Translated Mon Jul 26 21:58:26 JST 1999
.\"	by Shouichi Saito <ss236rx@ymg.urban.ne.jp>
.\" Proofed Tue Aug 17 1999 by NAKANO Takeo <nakano@apm.seikei.ac.jp>
.\"
.TH CMSG 3 1998-10-02 "Linux" "Linux Programmer's Manual"
.SH ̾
CMSG_ALIGN, CMSG_SPACE, CMSG_NXTHDR, CMSG_FIRSTHDR \- ǡ˥롣
.SH 
.B #include <sys/socket.h>
.sp
.BI "struct cmsghdr *CMSG_FIRSTHDR(struct msghdr *" msgh );
.br
.BI "struct cmsghdr *CMSG_NXTHDR(struct msghdr *" msgh ", struct cmsghdr *" cmsg );
.br
.BI "size_t CMSG_ALIGN(size_t " length );
.br
.BI "size_t CMSG_SPACE(size_t " length );
.br
.BI "size_t CMSG_LEN(size_t " length );
.br
.BI "unsigned char *CMSG_DATA(struct cmsghdr *" cmsg );
.sp
.nf
struct cmsghdr {
    socklen_t cmsg_len;    /* data byte count, including header */
    int       cmsg_level;  /* originating protocol */
    int       cmsg_type;   /* protocol-specific type */
    /* followed by unsigned char cmsg_data[]; */
};
.fi
.SH 
Υޥå
(ǡ (ancillary data) ȤƤФ) ꡢ
˥뤿˻Ȥ롣
åϥåȤˤΤǡǤϤʤ
ϡ夷ѥåȤؤΥ󥿡ե͡ʤޤ
Ȥʤإåեɡ顼Ҥγĥեǥ
ץν䡢Unixˤ뿮 (credential) ޤǤ롣
åϡ㤨 IP ץΤ褦ɲåإåեɤ
Τ˻ȤǤ롣
ǡϡ
.BR sendmsg (2)
ƤӽФꡢ
.BR recvmsg (2)
ƤӽФƼ롣
ܺ٤ϤΥޥ˥奢ڡ򻲾ȡ
.PP
ǡ
.I struct cmsghdr
¤ΤΥ󥹤ɲåǡղä줿ΤǤ롣
Υ󥹤ˤϤΥޥ˥奢ڡ˽񤫤Ƥ
ޥȤäƥ٤ǡľܥ٤ǤϤʤ
ѲǽåΥפˤĤƤϡ
줾ΥץȥΥޥ˥奢ڡ򻲾ȤΤȡ
³κѥХåե
.I net.core.optmem_max
sysctl ȤäǤ롣
.BR socket (7)
򻲾ȡ
.PP
.BR CMSG_FIRSTHDR ()
ϡϤ
.I msghdr
˴ϢǡХåեΡǽ
.I cmsghdr
ؤΥݥ󥿤֤
.PP
.BR CMSG_NXTHDR ()
ϡϤ
.I cmsghdr
μˤ (ͭ)
.I cmsghdr
֤
Хåե˽ʬʶ̵硢NULL ֤
.PP
.BR CMSG_ALIGN ()
ĹͿȡɬפʥ饤Ȥ̣Ĺ֤Ƥ롣
Ǥ롣
.PP
.BR CMSG_SPACE ()
ϡͿǡĹΤɬפ (ancillary element) 
Хȿ֤Ǥ롣
.PP
.BR CMSG_DATA ()
ϡ
.I cmsghdr
ΥǡʬؤΥݥ󥿤֤
.PP
.BR CMSG_LEN ()
ϡ
.I cmsghdr
¤Τ
.I cmsg_len
Ф˥ǡǼݤɬפ֤ͤ饤Ȥθ
롣
ȤƥǡĹȤ롣Ǥ롣
.PP
ǡ뤿ˤϺǽ
.I msghdr
ΥС
.I msg_controllen
åХåեĹǽ롣
.BR CMSG_FIRSTHDR ()

.I msghdr
ѤȺǽå졢
.B CMSG_NEXTHDR
Ȥȼå롣
줾åǤϡ
.I cmsg_len

.RB ( CMSG_LEN ()
Ȥ)
¾
.I cmsghdr
إåեɡƥǡʬФƤ
.BR CMSG_DATA ()
Ȥäƽ򤹤롣
Ǹ
.I msghdr

.I msg_controllen
եɤˡХåեåĹ
.BR CMSG_SPACE ()
ιפåȤ롣
.I msghdr
ˤĤƤξܺ٤
.BR recvmsg (2)
򻲾ȡ
.PP
åХåեƤΥåǼΤˤû硢
.I msghdr

.I msg_flags
С
.B MSG_CTRUNC
ե饰åȤ롣
.SH 
ǡǥϡPOSIX.1g draft, 4.4BSD-Lite, RFC\ 2292 
ҤƤ IPv6 advanced API,  SUSv2
˽򤷤Ƥ롣
.B CMSG_ALIGN
 Linux γĥǤ롣
.SH 
ܿΤˡǡؤΥˤϡ
ǽҤ٤ƤޥȤˤ٤Ǥ롣
.BR CMSG_ALIGN ()
 Linux ǤγĥǤꡢܿͤץǤϻȤ٤ǤϤʤ
.PP
Linux Ǥ
.BR CMSG_LEN (),
.BR CMSG_DATA (),
.BR CMSG_ALIGN ()
Ǥ (ΰȤߤʤ)
ΤȤϡѿΥΤ˻Ȥ롣
ܿϤʤʤ
.SH 
ΥɤϡäХåե
.B IP_TTL
ץõΤǤ롣
.PP
.in +4n
.nf
struct msghdr msgh;
struct cmsghdr *cmsg;
int *ttlptr;
int received_ttl;

/* Receive auxiliary data in msgh */
for (cmsg = CMSG_FIRSTHDR(&msgh); cmsg != NULL;
        cmsg = CMSG_NXTHDR(&msgh,cmsg)) {
    if (cmsg\->cmsg_level == IPPROTO_IP
            && cmsg\->cmsg_type == IP_TTL) {
        ttlptr = (int *) CMSG_DATA(cmsg);
        received_ttl = *ttlptr;
        break;
    }
}
if (cmsg == NULL) {
    /*
     * Error: IP_TTL not enabled or small buffer
     * or I/O error.
     */
}
.fi
.in
.PP
ʲΥɤϡ
.B SCM_RIGHTS
Ȥեǥץ Unix åȤ̤ΤǤ롣
.PP
.in +4n
.nf
struct msghdr msg = {0};
struct cmsghdr *cmsg;
int myfds[NUM_FD]; /* Contains the file descriptors to pass. */
char buf[CMSG_SPACE(sizeof myfds)];  /* ancillary data buffer */
int *fdptr;

msg.msg_control = buf;
msg.msg_controllen = sizeof buf;
cmsg = CMSG_FIRSTHDR(&msg);
cmsg\->cmsg_level = SOL_SOCKET;
cmsg\->cmsg_type = SCM_RIGHTS;
cmsg\->cmsg_len = CMSG_LEN(sizeof(int) * NUM_FD);
/* Initialize the payload: */
fdptr = (int *) CMSG_DATA(cmsg);
memcpy(fdptr, myfds, NUM_FD * sizeof(int));
/* Sum of the length of all control messages in the buffer: */
msg.msg_controllen = cmsg\->cmsg_len;
.fi
.in
.SH Ϣ
.BR recvmsg (2),
.BR sendmsg (2)
.PP
RFC\ 2292