backend/headless: stop picking a DRM FD

Sometimes the headless backend is used standalone with the Pixman
renderer, sometimes it's used together with another backend which
has already picked a DRM FD. In both of these cases it doesn't make
sense to pick a DRM FD.

Broadly speaking the headless backend doesn't really care which DRM
device is used for the buffers it receives. So it doesn't really
make sense to tie it to a particular DRM device.

Let the backend users (e.g. wlr_renderer_autocreate) open an arbitrary
DRM FD as needed instead.

backend/headless/backend.c

@@ -1,16 +1,9 @@
-#define _POSIX_C_SOURCE 200809L
 #include <assert.h>
-#include <drm_fourcc.h>
-#include <fcntl.h>
 #include <stdlib.h>
-#include <unistd.h>
 #include <wlr/interfaces/wlr_input_device.h>
 #include <wlr/interfaces/wlr_output.h>
-#include <wlr/render/wlr_renderer.h>
 #include <wlr/util/log.h>
-#include <xf86drm.h>
 #include "backend/headless.h"
-#include "render/drm_format_set.h"
 #include "util/signal.h"
 
 struct wlr_headless_backend *headless_backend_from_backend(
@@ -64,16 +57,9 @@ static void backend_destroy(struct wlr_backend *wlr_backend) {
 
 	wlr_backend_finish(wlr_backend);
 
-	close(backend->drm_fd);
 	free(backend);
 }
 
-static int backend_get_drm_fd(struct wlr_backend *wlr_backend) {
-	struct wlr_headless_backend *backend =
-		headless_backend_from_backend(wlr_backend);
-	return backend->drm_fd;
-}
-
 static uint32_t get_buffer_caps(struct wlr_backend *wlr_backend) {
 	return WLR_BUFFER_CAP_DATA_PTR
 		| WLR_BUFFER_CAP_DMABUF
@@ -83,7 +69,6 @@ static uint32_t get_buffer_caps(struct wlr_backend *wlr_backend) {
 static const struct wlr_backend_impl backend_impl = {
 	.start = backend_start,
 	.destroy = backend_destroy,
-	.get_drm_fd = backend_get_drm_fd,
 	.get_buffer_caps = get_buffer_caps,
 };
 
@@ -107,52 +92,6 @@ static bool backend_init(struct wlr_headless_backend *backend,
 	return true;
 }
 
-static int open_drm_render_node(void) {
-	uint32_t flags = 0;
-	int devices_len = drmGetDevices2(flags, NULL, 0);
-	if (devices_len < 0) {
-		wlr_log(WLR_ERROR, "drmGetDevices2 failed: %s", strerror(-devices_len));
-		return -1;
-	}
-	drmDevice **devices = calloc(devices_len, sizeof(drmDevice *));
-	if (devices == NULL) {
-		wlr_log_errno(WLR_ERROR, "Allocation failed");
-		return -1;
-	}
-	devices_len = drmGetDevices2(flags, devices, devices_len);
-	if (devices_len < 0) {
-		free(devices);
-		wlr_log(WLR_ERROR, "drmGetDevices2 failed: %s", strerror(-devices_len));
-		return -1;
-	}
-
-	int fd = -1;
-	for (int i = 0; i < devices_len; i++) {
-		drmDevice *dev = devices[i];
-		if (dev->available_nodes & (1 << DRM_NODE_RENDER)) {
-			const char *name = dev->nodes[DRM_NODE_RENDER];
-			wlr_log(WLR_DEBUG, "Opening DRM render node '%s'", name);
-			fd = open(name, O_RDWR | O_CLOEXEC);
-			if (fd < 0) {
-				wlr_log_errno(WLR_ERROR, "Failed to open '%s'", name);
-				goto out;
-			}
-			break;
-		}
-	}
-	if (fd < 0) {
-		wlr_log(WLR_ERROR, "Failed to find any DRM render node");
-	}
-
-out:
-	for (int i = 0; i < devices_len; i++) {
-		drmFreeDevice(&devices[i]);
-	}
-	free(devices);
-
-	return fd;
-}
-
 struct wlr_backend *wlr_headless_backend_create(struct wl_display *display) {
 	wlr_log(WLR_INFO, "Creating headless backend");
 
@@ -163,21 +102,12 @@ struct wlr_backend *wlr_headless_backend_create(struct wl_display *display) {
 		return NULL;
 	}
 
-	backend->drm_fd = open_drm_render_node();
-	if (backend->drm_fd < 0) {
-		wlr_log(WLR_ERROR, "Failed to open DRM render node");
-	}
-
 	if (!backend_init(backend, display)) {
-		goto error_init;
+		free(backend);
+		return NULL;
 	}
 
 	return &backend->backend;
-
-error_init:
-	close(backend->drm_fd);
-	free(backend);
-	return NULL;
 }
 
 struct wlr_backend *wlr_headless_backend_create_with_renderer(
@@ -191,27 +121,12 @@ struct wlr_backend *wlr_headless_backend_create_with_renderer(
 		return NULL;
 	}
 
-	int drm_fd = wlr_renderer_get_drm_fd(renderer);
-	if (drm_fd < 0) {
-		wlr_log(WLR_ERROR, "Failed to get DRM device FD from parent renderer");
-		backend->drm_fd = -1;
-	} else {
-		backend->drm_fd = fcntl(drm_fd, F_DUPFD_CLOEXEC, 0);
-		if (backend->drm_fd < 0) {
-			wlr_log_errno(WLR_ERROR, "fcntl(F_DUPFD_CLOEXEC) failed");
-		}
-	}
-
 	if (!backend_init(backend, display)) {
-		goto error_init;
+		free(backend);
+		return NULL;
 	}
 
 	return &backend->backend;
-
-error_init:
-	close(backend->drm_fd);
-	free(backend);
-	return NULL;
 }
 
 bool wlr_backend_is_headless(struct wlr_backend *backend) {

backend/headless/output.c

@@ -2,7 +2,6 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <wlr/interfaces/wlr_output.h>
-#include <wlr/render/wlr_renderer.h>
 #include <wlr/util/log.h>
 #include "backend/headless.h"
 #include "util/signal.h"

include/backend/headless.h

@@ -8,7 +8,6 @@
 
 struct wlr_headless_backend {
 	struct wlr_backend backend;
-	int drm_fd;
 	struct wl_display *display;
 	struct wl_list outputs;
 	size_t last_output_num;