child_stderr_to_file.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
    int pipefd[2];
    if (pipe(pipefd) == -1) {
        perror("pipe");
        exit(EXIT_FAILURE);
    }
    pid_t pid = fork();
    if (pid < 0) {
        perror("fork");
        close(pipefd[0]);
        close(pipefd[1]);
        exit(EXIT_FAILURE);
    } else if (pid == 0) {
        close(pipefd[0]);
        dup2(pipefd[1], 2);
        close(pipefd[1]);
        execlp("dd", "dd", "if=/dev/zero", "of=dd.bin", "bs=1024M", "count=10", (char *)NULL);
        perror("dd");
        exit(EXIT_FAILURE);
    } else {
        close(pipefd[1]);
        char buf[512];
        ssize_t ret;
        int fd = open("dd.log", O_CREAT | O_RDWR, S_IRUSR | S_IWUSR);
        while ((ret = read(pipefd[0], buf, sizeof(buf))) > 0) {
            write(fd, buf, ret);
        }
        close(pipefd[0]);
        close(fd);
        int wstatus;
        pid_t w = waitpid(pid, &wstatus, 0);
        if (w < 0) {
            perror("waitpid");
            exit(EXIT_FAILURE);
        }
        if (WIFEXITED(wstatus)) {
            int exit_code = WEXITSTATUS(wstatus);
            printf("child exit code = %d\n", exit_code);
        } else {
            printf("child status = %04x\n", wstatus);
        }
        printf("parent process end\n");
    }
    return 0;
}

wipe_disk.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <unistd.h>

int wipe_disk(const char *name)
{
    int pipefd[2];
    if (pipe(pipefd) == -1) {
        perror("pipe");
        return 0;
    }
    pid_t cpid = fork();
    if (cpid < 0) {
        perror("fork");
        close(pipefd[0]);
        close(pipefd[1]);
        return 0;
    } else if (cpid == 0) {
        close(pipefd[0]);
        dup2(pipefd[1], 2);
        close(pipefd[1]);
        char of[64];
        sprintf(of, "of=%s.bin", name);
        char *const cmd[] = {"/usr/bin/dd", "if=/dev/zero", of, "bs=1024M", "count=1", NULL};
        execv("/usr/bin/dd", cmd);
        perror("execv");
        return 0;
    } else {
        close(pipefd[1]);
        char buf[512];
        ssize_t r;
        char log[64];
        sprintf(log, "%s.log", name);
        int fd = open(log, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR);
        while ((r = read(pipefd[0], buf, sizeof(buf))) > 0) {
            write(fd, buf, r);
        }
        close(pipefd[0]);
        close(fd);
        int wstatus;
        pid_t w = waitpid(cpid, &wstatus, 0);
        if (w < 0) {
            perror("waitpid");
            return 0;
        }
        if (WIFEXITED(wstatus)) {
            int exit_code = WEXITSTATUS(wstatus);
            printf("child exit code = %d\n", exit_code);
        } else {
            printf("child status = %04x\n", wstatus);
        }
        printf("parent process end\n");
    }
    return 1;
}

int main(int argc, char *argv[])
{
    int count = 0;
    char name[64];
    for (int i = 'b'; i <= 'm'; i++) {
        sprintf(name, "sd%c", i);
        pid_t cpid = fork();
        if (cpid < 0) {
            perror("fork");
            exit(EXIT_FAILURE);
        } else if (cpid == 0) {
            wipe_disk(name) ? exit(EXIT_SUCCESS) : exit(EXIT_FAILURE);
        } else {
            count++;
        }
    }
    for (int i = 0; i < count; i++) {
        int wstatus;
        pid_t w = wait(&wstatus);
        if (WIFEXITED(wstatus)) {
            int exit_code = WEXITSTATUS(wstatus);
            printf("child exit code = %d\n", exit_code);
        } else {
            printf("child status = %04x\n", wstatus);
        }
        printf("parent process end\n");
    }
    return 0;
}