/* cc -o t-journal-tail t-journal-tail.c -lsystemd-journal
 */

#include <stdio.h>
#include <stdlib.h>
#include <systemd/sd-journal.h>

void
check (int r)
{
  if (r < 0)
    {
      fprintf (stderr, "%s\n", strerror(-r));
      exit (1);
    }
}

void
checkv (const char *label, int r)
{
  if (r < 0)
    {
      fprintf (stderr, "%s: %s\n", label, strerror(-r));
      exit (1);
    }
  fprintf (stderr, "%s: %d\n", label, r);
}

void
dump (sd_journal *j, int count)
{
  int i = 0;
  while (i < count) {
    const void *data;
    size_t size;
    uint64_t usec;
    int r;

    check (sd_journal_get_realtime_usec (j, &usec));
    check (sd_journal_get_data (j, "MESSAGE", &data, &size));
    printf ("%lld %.*s\n", usec, size, data);

    i++;
    if (i >= count)
      break;

    check (r = sd_journal_next (j));
    if (r == 0)
      break;
  }
}

void
main ()
{
  sd_journal *j;

  check (sd_journal_open (&j, 0));
  check (sd_journal_seek_tail (j));
  checkv ("next", sd_journal_next (j));
  dump (j, 5);
}