MMAP

• mmap is highly similar as shared memory, base on the same kernel implementation.

The simplest code snippet of mmap

#include "apue.h"


#include <sys/mman.h>
#include <string.h>
#include <fcntl.h>

#define PATH    "/workspace/c/apue/mmap_x"
#define MESG    "Oh Scent"

#define SIZE   1024 

char *
mmap_init() {
    char *ptr;
    int fd;

    if ((fd = open(PATH, O_RDWR)) < 0) {
        err_sys("open failed");
    }


    if ((ptr = (char *)mmap(0, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED) {
        err_sys("mmap failed");
    }

    return ptr;
}

void
mmap_set(char *ptr) {
}



int
main(void) {

    char *ptr;
    pid_t pid;

    if ((pid = fork()) < 0) {
        err_sys("fork failed");
    } else if (pid == 0) { 
        //child

        ptr = mmap_init();
        printf("child read from mmap file:%s\n", ptr);
        exit(0);
    }

    ptr = mmap_init();
    strncpy(ptr, MESG, strlen(MESG));
    printf("parent write to mmap file\n");

    wait(pid);

    exit(0);
}