// gcc -Og -Wall -Wextra $(pkg-config --cflags libdrm) -o list-kms-devices list-kms-devices.c $(pkg-config --libs libdrm)

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <xf86drm.h>

int main()
{
	for( int i = 0; i < DRM_MAX_MINOR; ++i ) {
		char path[ 32 ];  // this is plenty for this purpose
		sprintf( path, DRM_DEV_NAME, DRM_DIR_NAME, i );

		int fd = open( path, O_RDWR | O_CLOEXEC | O_NOCTTY | O_NONBLOCK );
		if( fd < 0 ) {
			if( errno != ENOENT )
				fprintf( stderr, "%s: %m\n", path );
			continue;
		}

		if( drmSetClientCap( fd, DRM_CLIENT_CAP_ATOMIC, 1 ) >= 0 ) {
			printf( "%s:\n", path );

			drmVersionPtr v = drmGetVersion( fd );
			printf( "\tdriver: %s (%s)\n", v->name, v->desc );
			printf( "\tversion: v%d.%d.%d (%s)\n", v->version_major, v->version_minor, v->version_patchlevel, v->date );
			drmFreeVersion( v );
		}

		close( fd );
	}
	return 0;
}