linux msgsnd() max

msgqueue_max.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <unistd.h>

#define FTOK_FNAME  "msgq.dat"
#define FTOK_CHAR   'b'
#define SZ_BUF      (8192)

struct my_msgbuf {
    long mtype;
    char mtext[SZ_BUF + 256];
};


static int msg_send(void)
{
    struct my_msgbuf buf;
    int msqid;
    key_t key;

    if ((key = ftok(FTOK_FNAME, FTOK_CHAR)) == -1) {
        perror("ftok");
        exit(1);
    }

    if ((msqid = msgget(key, 0644 | IPC_CREAT)) == -1) {
        perror("msgget");
        exit(1);
    }

    printf("send after 5sec...\n");
    sleep(5);

    buf.mtype = 1;
    memset(buf.mtext, 0x77, SZ_BUF + 256);
    if (msgsnd(msqid, &buf, SZ_BUF, 0) == -1) {
        perror("msgsnd");
    }

    if (msgctl(msqid, IPC_RMID, NULL) == -1) {
        perror("msgctl");
        exit(1);
    }

    return 0;
}


static int msg_recv(void)
{
    struct my_msgbuf buf;
    int msqid;
    key_t key;

    if ((key = ftok(FTOK_FNAME, FTOK_CHAR)) == -1) {
        perror("ftok");
        exit(1);
    }

    if ((msqid = msgget(key, 0644)) == -1) {
        perror("msgget");
        exit(1);
    }

    memset(buf.mtext, 0xcc, SZ_BUF + 256);
    if (msgrcv(msqid, &buf, SZ_BUF, 0, 0) == -1) {
        perror("msgrcv");
        exit(1);
    }

    for (int lp = 0; lp < SZ_BUF + 256; lp++) {
        if (buf.mtext[lp] != 0x77) {
            printf("mismatch at %d !\n", lp);
            break;
        }
    }

    return 0;
}


int main(int argc, char *argv[])
{
    switch (argv[1][0]) {
    case '0':
        msg_send();
        break;
    case '1':
        msg_recv();
        break;
    }

    return 0;
}