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Toute la documentation sur la certification Linux LPI

cmsg

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CMSG_ALIGN, CMSG_SPACE, CMSG_NXTHDR, CMSG_FIRSTHDR - Êä½õ¥Ç¡¼¥¿¤Ë¥¢¥¯¥»¥¹¤¹¤ë¡£

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#include <sys/socket.h>

struct cmsghdr *CMSG_FIRSTHDR(struct msghdr *msgh);
struct cmsghdr *CMSG_NXTHDR(struct msghdr *msgh, struct cmsghdr *cmsg);
size_t CMSG_ALIGN(size_t length);
size_t CMSG_SPACE(size_t length);
size_t CMSG_LEN(size_t length);
unsigned char *CMSG_DATA(struct cmsghdr *cmsg);

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[]; */

};

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Êä½õ¥Ç¡¼¥¿¤Ï struct cmsghdr ¹½Â¤ÂΤΥ·¡¼¥±¥ó¥¹¤ËÄɲåǡ¼¥¿¤¬Éղ䵤줿¤â¤Î¤Ç¤¢¤ë¡£ ¤³¤Î¥·¡¼¥±¥ó¥¹¤Ë¤Ï¤³¤Î¥Þ¥Ë¥å¥¢¥ë¥Ú¡¼¥¸¤Ë½ñ¤«¤ì¤Æ¤¤¤ë ¥Þ¥¯¥í¤ò»È¤Ã¤Æ¥¢¥¯¥»¥¹¤¹¤Ù¤­¤Ç¡¢Ä¾ÀÜ¥¢¥¯¥»¥¹¤¹¤Ù¤­¤Ç¤Ï¤Ê¤¤¡£ »ÈÍѲÄǽ¤ÊÀ©¸æ¥á¥Ã¥»¡¼¥¸¤Î¥¿¥¤¥×¤Ë¤Ä¤¤¤Æ¤Ï¡¢ ¤½¤ì¤¾¤ì¤Î¥×¥í¥È¥³¥ë¤Î¥Þ¥Ë¥å¥¢¥ë¥Ú¡¼¥¸¤ò»²¾È¤Î¤³¤È¡£ ÀܳËè¤ÎºÇÂçÊä½õÍѥХåե¡¥µ¥¤¥º¤Ï net.core.optmem_max sysctl ¤ò»È¤Ã¤ÆÀßÄê¤Ç¤­¤ë¡£ socket(7) ¤ò»²¾È¡£

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Linux ¤Ç¤Ï CMSG_LEN(), CMSG_DATA(), CMSG_ALIGN() ¤ÏÄê¿ô¼°¤Ç¤¢¤ë (¤½¤ì¤é¤Î°ú¿ô¤¬Äê¿ô¤È¤ß¤Ê¤µ¤ì¤ë)¡£ ¤³¤Î¤³¤È¤Ï¡¢¹­°èÊÑ¿ô¤Î¥µ¥¤¥º¤òÀë¸À¤¹¤ë¤Î¤Ë»È¤¨¤ë¡£ ¤·¤«¤·°Ü¿¢À­¤Ï¤Ê¤¯¤Ê¤ë¤À¤í¤¦¡£

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¼¡¤Î¥³¡¼¥É¤Ï¡¢¼õ¤±¼è¤Ã¤¿Êä½õ¥Ð¥Ã¥Õ¥¡¤«¤é IP_TTL ¥ª¥×¥·¥ç¥ó¤òõ¤¹¤â¤Î¤Ç¤¢¤ë¡£

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.

     */

}

°Ê²¼¤Î¥³¡¼¥É¤Ï¡¢ SCM_RIGHTS ¤ò»È¤¤¡¢¥Õ¥¡¥¤¥ë¥Ç¥¹¥¯¥ê¥×¥¿¤ÎÇÛÎó¤ò Unix¥½¥±¥Ã¥È¤òÄ̤·¤ÆÁ÷¤ë¤â¤Î¤Ç¤¢¤ë¡£

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;

´ØÏ¢¹àÌÜ

recvmsg(2), sendmsg(2)

RFC 2292