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nerves_runtime

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Small, general runtime utilities for Nerves devices

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nerves_runtime src log_tailer.c
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src/log_tailer.c 

#include <err.h>

#include <fcntl.h>

#include <stdlib.h>

#include <string.h>

#include <sys/stat.h>

#include <sys/un.h>

#include <unistd.h>

#include <arpa/inet.h>



#define KMSG_PATH "/proc/kmsg"

#define SYSLOG_PATH "/dev/log"

#define BUFFER_SIZE 1024



static char buffer[BUFFER_SIZE];



static void usage()

{

    errx(EXIT_FAILURE, "Specify either syslog or kmsg as the parameter");

}



static int open_syslog()

{

    int fd = socket(AF_UNIX, SOCK_DGRAM, 0);

    if (fd < 0)

        err(EXIT_FAILURE, "socket");



    // Erase the old log file (if any) so that we can bind to it

    unlink(SYSLOG_PATH);



    struct sockaddr_un addr;

    memset(&addr, 0, sizeof(addr));

    addr.sun_family = AF_UNIX;

    strcpy(addr.sun_path, SYSLOG_PATH);



    if (bind(fd, (struct sockaddr *) &addr, sizeof(addr)) < 0)

        err(EXIT_FAILURE, "bind %s", SYSLOG_PATH);



    // Make the syslog file writable

    chmod(SYSLOG_PATH, 0666);



    return fd;

}



static int open_klog()

{

    int fd = open(KMSG_PATH, O_RDONLY);

    if (fd < 0)

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

    return fd;

}



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

{

    if (argc != 2)

        usage();



    int fd = 0;

    if (strcmp(argv[1], "syslog"))

        fd = open_syslog();

    else if (strcmp(argv[1], "kmsg"))

        fd = open_klog();

    else

        usage();



    for (;;) {

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

        if (amt < 0)

            err(EXIT_FAILURE, "%s: read", argv[1]);



        if (write(STDOUT_FILENO, &buffer, amt) < 0)

            err(EXIT_FAILURE, "%s: write", argv[1]);

    }

}