text: #include <assert.h>
  #include <errno.h>
  #include <drm_fourcc.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <unistd.h>
  #include <wayland-server-core.h>
  #include <wlr/backend/interface.h>
  #include <wlr/backend/session.h>
  #include <wlr/interfaces/wlr_output.h>
  #include <wlr/types/wlr_list.h>
  #include <wlr/util/log.h>
  #include <xf86drm.h>
  #include "backend/drm/drm.h"
  #include "types/wlr_buffer.h"
  #include "util/signal.h"
  
  struct wlr_drm_backend *get_drm_backend_from_backend(
  		struct wlr_backend *wlr_backend) {
  	assert(wlr_backend_is_drm(wlr_backend));
  	return (struct wlr_drm_backend *)wlr_backend;
  }
  
  static bool backend_start(struct wlr_backend *backend) {
  	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
  	scan_drm_connectors(drm);
  	return true;
  }
  
  static void backend_destroy(struct wlr_backend *backend) {
  	if (!backend) {
  		return;
  	}
  
  	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
  
  	restore_drm_outputs(drm);
  
  	struct wlr_drm_connector *conn, *next;
  	wl_list_for_each_safe(conn, next, &drm->outputs, link) {
  		destroy_drm_connector(conn);
  	}
  
  	wlr_backend_finish(backend);
  
  	struct wlr_drm_fb *fb, *fb_tmp;
  	wl_list_for_each_safe(fb, fb_tmp, &drm->fbs, link) {
  		drm_fb_destroy(fb);
  	}
  
  	wl_list_remove(&drm->display_destroy.link);
  	wl_list_remove(&drm->session_destroy.link);
  	wl_list_remove(&drm->session_active.link);
  	wl_list_remove(&drm->parent_destroy.link);
  	wl_list_remove(&drm->dev_change.link);
  	wl_list_remove(&drm->dev_remove.link);
  
  	finish_drm_resources(drm);
  	finish_drm_renderer(&drm->renderer);
  
  	free(drm->name);
  	wlr_session_close_file(drm->session, drm->dev);
  	wl_event_source_remove(drm->drm_event);
  	free(drm);
  }
  
  static struct wlr_renderer *backend_get_renderer(
  		struct wlr_backend *backend) {
  	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
  
  	if (drm->parent) {
  		return drm->parent->renderer.wlr_rend;
  	} else {
  		return drm->renderer.wlr_rend;
  	}
  }
  
  static clockid_t backend_get_presentation_clock(struct wlr_backend *backend) {
  	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
  	return drm->clock;
  }
  
  static int backend_get_drm_fd(struct wlr_backend *backend) {
  	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
  
  	if (drm->parent) {
  		return drm->parent->fd;
  	} else {
  		return drm->fd;
  	}
  }
  
  static uint32_t backend_get_buffer_caps(struct wlr_backend *backend) {
  	return WLR_BUFFER_CAP_DMABUF;
  }
  
  static const struct wlr_backend_impl backend_impl = {
  	.start = backend_start,
  	.destroy = backend_destroy,
  	.get_renderer = backend_get_renderer,
  	.get_presentation_clock = backend_get_presentation_clock,
  	.get_drm_fd = backend_get_drm_fd,
  	.get_buffer_caps = backend_get_buffer_caps,
  };
  
  bool wlr_backend_is_drm(struct wlr_backend *b) {
  	return b->impl == &backend_impl;
  }
  
  static void handle_session_active(struct wl_listener *listener, void *data) {
  	struct wlr_drm_backend *drm =
  		wl_container_of(listener, drm, session_active);
  	struct wlr_session *session = drm->session;
  
  	if (session->active) {
  		wlr_log(WLR_INFO, "DRM fd resumed");
  		scan_drm_connectors(drm);
  
  		struct wlr_drm_connector *conn;
  		wl_list_for_each(conn, &drm->outputs, link) {
  			struct wlr_output_mode *mode = NULL;
  			if (conn->output.enabled && conn->output.current_mode != NULL) {
  				mode = conn->output.current_mode;
  			}
  			struct wlr_output_state state = {
  				.committed = WLR_OUTPUT_STATE_MODE | WLR_OUTPUT_STATE_ENABLED,
  				.enabled = mode != NULL,
  				.mode_type = WLR_OUTPUT_STATE_MODE_FIXED,
  				.mode = mode,
  			};
  			drm_connector_commit_state(conn, &state);
  		}
  	} else {
  		wlr_log(WLR_INFO, "DRM fd paused");
  	}
  }
  
  static void handle_dev_change(struct wl_listener *listener, void *data) {
  	struct wlr_drm_backend *drm = wl_container_of(listener, drm, dev_change);
  
  	if (!drm->session->active) {
  		return;
  	}
  
  	wlr_log(WLR_DEBUG, "%s invalidated", drm->name);
  	scan_drm_connectors(drm);
  }
  
  static void handle_dev_remove(struct wl_listener *listener, void *data) {
  	struct wlr_drm_backend *drm = wl_container_of(listener, drm, dev_remove);
  
  	wlr_log(WLR_INFO, "Destroying DRM backend for %s", drm->name);
  	backend_destroy(&drm->backend);
  }
  
  static void handle_session_destroy(struct wl_listener *listener, void *data) {
  	struct wlr_drm_backend *drm =
  		wl_container_of(listener, drm, session_destroy);
  	backend_destroy(&drm->backend);
  }
  
  static void handle_display_destroy(struct wl_listener *listener, void *data) {
  	struct wlr_drm_backend *drm =
  		wl_container_of(listener, drm, display_destroy);
  	backend_destroy(&drm->backend);
  }
  
  static void handle_parent_destroy(struct wl_listener *listener, void *data) {
  	struct wlr_drm_backend *drm =
  		wl_container_of(listener, drm, parent_destroy);
  	backend_destroy(&drm->backend);
  }
  
  struct wlr_backend *wlr_drm_backend_create(struct wl_display *display,
  		struct wlr_session *session, struct wlr_device *dev,
  		struct wlr_backend *parent) {
  	assert(display && session && dev);
  	assert(!parent || wlr_backend_is_drm(parent));
  
  	char *name = drmGetDeviceNameFromFd2(dev->fd);
  	drmVersion *version = drmGetVersion(dev->fd);
  	wlr_log(WLR_INFO, "Initializing DRM backend for %s (%s)", name, version->name);
  	drmFreeVersion(version);
  
  	struct wlr_drm_backend *drm = calloc(1, sizeof(struct wlr_drm_backend));
  	if (!drm) {
  		wlr_log_errno(WLR_ERROR, "Allocation failed");
  		return NULL;
  	}
  	wlr_backend_init(&drm->backend, &backend_impl);
  
  	drm->session = session;
  	wl_list_init(&drm->fbs);
  	wl_list_init(&drm->outputs);
  
  	drm->dev = dev;
  	drm->fd = dev->fd;
  	drm->name = name;
  
  	if (parent != NULL) {
  		drm->parent = get_drm_backend_from_backend(parent);
  
  		drm->parent_destroy.notify = handle_parent_destroy;
  		wl_signal_add(&parent->events.destroy, &drm->parent_destroy);
  	} else {
  		wl_list_init(&drm->parent_destroy.link);
  	}
  
  	drm->dev_change.notify = handle_dev_change;
  	wl_signal_add(&dev->events.change, &drm->dev_change);
  
  	drm->dev_remove.notify = handle_dev_remove;
  	wl_signal_add(&dev->events.remove, &drm->dev_remove);
  
  	drm->display = display;
  
  	struct wl_event_loop *event_loop = wl_display_get_event_loop(display);
  	drm->drm_event = wl_event_loop_add_fd(event_loop, drm->fd,
  		WL_EVENT_READABLE, handle_drm_event, NULL);
  	if (!drm->drm_event) {
  		wlr_log(WLR_ERROR, "Failed to create DRM event source");
  		goto error_fd;
  	}
  
  	drm->session_active.notify = handle_session_active;
  	wl_signal_add(&session->events.active, &drm->session_active);
  
  	if (!check_drm_features(drm)) {
  		goto error_event;
  	}
  
  	if (!init_drm_resources(drm)) {
  		goto error_event;
  	}
  
  	if (!init_drm_renderer(drm, &drm->renderer)) {
  		wlr_log(WLR_ERROR, "Failed to initialize renderer");
  		goto error_event;
  	}
  
  	if (drm->parent) {
  		// We'll perform a multi-GPU copy for all submitted buffers, we need
  		// to be able to texture from them
  		struct wlr_renderer *renderer = drm->renderer.wlr_rend;
  		const struct wlr_drm_format_set *texture_formats =
  			wlr_renderer_get_dmabuf_texture_formats(renderer);
  		if (texture_formats == NULL) {
  			wlr_log(WLR_ERROR, "Failed to query renderer texture formats");
  			goto error_event;
  		}
  
  		for (size_t i = 0; i < texture_formats->len; i++) {
  			const struct wlr_drm_format *fmt = texture_formats->formats[i];
  			if (fmt->len == 0) {
  				// Modifiers aren't supported. The implicit modifier changes
  				// from a GPU to the other, so we can only accept linear
  				// buffers
  				wlr_drm_format_set_add(&drm->mgpu_formats, fmt->format,
  					DRM_FORMAT_MOD_LINEAR);
  				continue;
  			}
  
  			for (size_t j = 0; j < fmt->len; j++) {
  				wlr_drm_format_set_add(&drm->mgpu_formats, fmt->format,
  					fmt->modifiers[j]);
  			}
  		}
  	}
  
  	drm->session_destroy.notify = handle_session_destroy;
  	wl_signal_add(&session->events.destroy, &drm->session_destroy);
  
  	drm->display_destroy.notify = handle_display_destroy;
  	wl_display_add_destroy_listener(display, &drm->display_destroy);
  
  	return &drm->backend;
  
  error_event:
  	wl_list_remove(&drm->session_active.link);
  	wl_event_source_remove(drm->drm_event);
  error_fd:
  	wlr_session_close_file(drm->session, dev);
  	wl_list_remove(&drm->parent_destroy.link);
  	wl_list_remove(&drm->dev_change.link);
  	wl_list_remove(&drm->dev_remove.link);
  	free(drm);
  	return NULL;
  }
  