reopened fifo still has data

[adamdebek]

When all ends of fifo are closed, data should be discarded.
Reproduction:

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

int main(void) {
        int fd_w, fd_r;
        ssize_t ret;
        char *msg = "abcdefghifjklm";

        if (mkfifo("fifo", 0666) < 0) {
                perror("mkfifo");
                exit(EXIT_FAILURE);
        }

        if ((fd_r = open("fifo", O_RDONLY | O_NONBLOCK)) < 0) {
                perror("open");
                exit(EXIT_FAILURE);
        }

        if ((fd_w = open("fifo", O_WRONLY)) < 0) {
                perror("open");
                exit(EXIT_FAILURE);
        }

        if (write(fd_w, msg, strlen(msg)) != strlen(msg)) {
                perror("write");
                exit(EXIT_FAILURE);
        }

        close(fd_r);
        close(fd_w);

        if ((fd_r = open("fifo", O_RDONLY | O_NONBLOCK)) < 0) {
                perror("open");
                exit(EXIT_FAILURE);
        }

        if ((fd_w = open("fifo", O_WRONLY)) < 0) {
                perror("open");
                exit(EXIT_FAILURE);
        }

        if ((ret = read(fd_r, msg, strlen(msg))) < 0) {
                perror("read");
                exit(EXIT_FAILURE);
        }

        printf("read: %zd\n", ret);
        printf("errno: %d\n", errno);

        return 0;
}