mmap 系统调用中 MAP_ANONYMOUS 标志的用途是什么

使用mmap系统调用中的MAP_ANONYMOUS标志

c
#include 
#include 
#include 
#include 
int main() {
    size_t size = 4096; // 4KB
    // 创建匿名映射
    int *shared_memory = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
    if (shared_memory == MAP_FAILED) {
        perror("mmap");
        exit(EXIT_FAILURE);
    }
    // 在父子进程之间共享数据
    pid_t pid = fork();
    if (pid == -1) {
        perror("fork");
        exit(EXIT_FAILURE);
    }
    if (pid == 0) {
        // Child process
        printf("Child process writing to shared memory%
");
        *shared_memory = 123;
        exit(EXIT_SUCCESS);
    } else {
        // Parent process
        wait(NULL); // 等待子进程结束
        printf("Parent process read from shared memory: %d%
", *shared_memory);
        // 解除映射
        if (munmap(shared_memory, size) == -1) {
            perror("munmap");
            exit(EXIT_FAILURE);
        }
    }
    return 0;
}