c語言 實現 poen pclose

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <stdlib.h>

static pid_t *childpid = NULL;
static int max;

FILE *m_popen(const char *command, const char *type) {
    FILE *fp;
    int pfd[2];
    pid_t pid;
    
    if ((type[0] != 'r' && type[0] != 'w') || type[1] != '\0') {
        errno = EINVAL;
        return NULL;
    }
    
    if (childpid == NULL) {
        max = sysconf(_SC_OPEN_MAX);
        if ((childpid = (pid_t *)calloc(max, sizeof(pid_t))) == NULL) {
            return NULL;
        }
    }
    
    if (pipe(pfd) < 0) return NULL;

    if (pfd[0] >= max || pfd[1] >= max) {
        close(pfd[0]);
        close(pfd[1]);
        return NULL;
    }

    if ((pid = fork()) < 0) {
        return NULL;
    }

    if (pid == 0) {
        if (type[0] == 'r') {
            close(pfd[0]);
            if (pfd[1] != STDOUT_FILENO) {
                dup2(pfd[1], STDOUT_FILENO);
                close(pfd[1]);
            }
            else {
                close(pfd[1]);
                if (pfd[0] != STDIN_FILENO) {
                    dup2(pfd[0], STDIN_FILENO);
                    close(pfd[0]);
                }
            }
        }
        
        for (int i = 0; i <= max; i++) {
            if (childpid[i] > 0) close(i);
        }
        
        execl("/bin/sh", "sh", "-c", command, NULL);
        exit(0);
    }
    
    if (type[0] == 'r') {
        close(pfd[1]);
        if ((fp = fdopen(pfd[0], type)) == NULL) {
            return NULL;
        }
    }

    childpid[fileno(fp)] = pid;
    return fp;
}

int m_pclose(FILE *fp) {
    int status, fd, pid;
    if (childpid == NULL) {
        errno = EINVAL;
        return -1;
    }
    fd = fileno(fp);
    if (fd >= max) {
        errno = EINVAL;
        return -1;
    }
    pid = childpid[fd];
    if (pid == 0) {
        errno = EINVAL;
        return -1;
    }
    childpid[fd] = 0;
    waitpid(pid, &status, 0);
    return status;
}

int main() {
    FILE *fp;
    char buff[1024] = {0};
    if ((fp = m_popen("ls -al /etc", "r")) == NULL) {
        perror("m_popen");
        return 1;
    }
    while (fgets(buff, 1024, fp) != NULL) {
        printf("%s", buff);
    }
    m_pclose(fp);
    return 0;
}