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nerves_runtime

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Small, general runtime utilities for Nerves devices

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nerves_runtime src kmsg_tailer.c
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src/kmsg_tailer.c 

#include <err.h>

#include <errno.h>

#include <fcntl.h>

#include <poll.h>

#include <stdlib.h>

#include <sys/stat.h>

#include <unistd.h>



#define KMSG_PATH "/dev/kmsg"

#define BUFFER_SIZE 4096



static void handle_kmsg(int fd)

{

    char buffer[BUFFER_SIZE];

    ssize_t amt = read(fd, buffer, sizeof(buffer));

    if (amt < 0 && errno != EINTR)

        err(EXIT_FAILURE, "read %s", KMSG_PATH);



    while (amt > 0) {

        ssize_t written = write(STDOUT_FILENO, buffer, amt);

        if (written < 0 && errno != EINTR)

            err(EXIT_FAILURE, "write stdout");

        amt -= written;

    }

}



int kmsg_tailer_main(int argc, char *argv[])

{

    (void) argc;

    (void) argv;



    int fd = open(KMSG_PATH, O_RDONLY | O_CLOEXEC);

    if (fd < 0)

        err(EXIT_FAILURE, "open %s", KMSG_PATH);



    for (;;) {

        struct pollfd fdset[2];



        fdset[0].fd = fd;

        fdset[0].events = POLLIN;

        fdset[0].revents = 0;



        fdset[1].fd = STDIN_FILENO;

        fdset[1].events = POLLIN;

        fdset[1].revents = 0;



        int rc = poll(fdset, 2, -1);

        if (rc < 0) {

            // Retry if EINTR

            if (errno == EINTR)

                continue;



            err(EXIT_FAILURE, "poll");

        }



        if (fdset[0].revents & (POLLIN | POLLHUP))

            handle_kmsg(fd);



        // Any notification from Erlang is to exit

        if (fdset[1].revents & (POLLIN | POLLHUP))

            break;

    }



    return 0;

}