List the current mode of the CRTC.

listmode.c

/* gcc -o listmode listmode.c $(pkg-config --cflags --libs glib-2.0 libdrm) */

#include <glib.h>
#include <fcntl.h>
#include <stdlib.h>
#include <xf86drm.h>
#include <xf86drmMode.h>

int
main (int argc, char **argv)
{
  int i;
  int fd;
  drmModeRes *resources = NULL;
  drmModeConnector *connector = NULL;
  drmModeEncoder *encoder = NULL;
  drmModeCrtc *crtc = NULL;

  fd = open ("/dev/dri/card0", O_RDWR);
  if (fd < 0)
    {
      g_warning ("Unable to open DRI device");
      exit (1);
    }

  resources = drmModeGetResources (fd);

  /* Find the first active connector to display on. */
  for (i = 0; i < resources->count_connectors; i++)
    {
      connector = drmModeGetConnector (fd, resources->connectors[i]);
      if (connector == NULL)
        continue;

      if (connector->connection == DRM_MODE_CONNECTED &&
          connector->count_modes > 0)
        break;

      drmModeFreeConnector(connector);
    }

  if (i == resources->count_connectors)
    {
      g_warning ("Could not find an active connector");
      exit (1);
    }

  /* Find the CRTC. */
  encoder = drmModeGetEncoder (fd, connector->encoder_id);
  crtc = drmModeGetCrtc (fd, encoder->crtc_id);

  g_print ("The active connector's CRTC is %d, and is showing "
           "framebuffer %d, offset +%d,%d, mode %s.\n",
           crtc->crtc_id, crtc->buffer_id,
           crtc->x, crtc->y, crtc->mode.name);
  return 0;
}