backend/wayland: add basic linux-dmabuf feedback support

This patch makes it so we bind to zwp_linux_dmabuf_v1 version 4 and
we use it to grab the main device. v4 sends supported formats via a
table so we need to handle this as well.

v4 allows wlroots to remove the requirement for Mesa's internal
wl_drm interface.

backend/wayland/backend.c

@@ -4,6 +4,8 @@
 #include <limits.h>
 #include <stdint.h>
 #include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/types.h>
 #include <unistd.h>
 
 #include <drm_fourcc.h>
@@ -30,6 +32,21 @@
 #include "tablet-unstable-v2-client-protocol.h"
 #include "relative-pointer-unstable-v1-client-protocol.h"
 
+struct wlr_wl_linux_dmabuf_feedback_v1 {
+	struct wlr_wl_backend *backend;
+	dev_t main_device_id;
+	struct wlr_wl_linux_dmabuf_v1_table_entry *format_table;
+	size_t format_table_size;
+
+	dev_t tranche_target_device_id;
+};
+
+struct wlr_wl_linux_dmabuf_v1_table_entry {
+	uint32_t format;
+	uint32_t pad; /* unused */
+	uint64_t modifier;
+};
+
 struct wlr_wl_backend *get_wl_backend_from_backend(struct wlr_backend *backend) {
 	assert(wlr_backend_is_wl(backend));
 	return (struct wlr_wl_backend *)backend;
@@ -108,6 +125,119 @@ static const struct zwp_linux_dmabuf_v1_listener linux_dmabuf_v1_listener = {
 	.modifier = linux_dmabuf_v1_handle_modifier,
 };
 
+static void linux_dmabuf_feedback_v1_handle_done(void *data,
+		struct zwp_linux_dmabuf_feedback_v1 *feedback) {
+	// This space is intentionally left blank
+}
+
+static void linux_dmabuf_feedback_v1_handle_format_table(void *data,
+		struct zwp_linux_dmabuf_feedback_v1 *feedback, int fd, uint32_t size) {
+	struct wlr_wl_linux_dmabuf_feedback_v1 *feedback_data = data;
+
+	feedback_data->format_table = NULL;
+
+	void *table_data = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
+	if (table_data == MAP_FAILED) {
+		wlr_log_errno(WLR_ERROR, "failed to mmap DMA-BUF format table");
+	} else {
+		feedback_data->format_table = table_data;
+		feedback_data->format_table_size = size;
+	}
+	close(fd);
+}
+
+static void linux_dmabuf_feedback_v1_handle_main_device(void *data,
+		struct zwp_linux_dmabuf_feedback_v1 *feedback,
+		struct wl_array *dev_id_arr) {
+	struct wlr_wl_linux_dmabuf_feedback_v1 *feedback_data = data;
+
+	dev_t dev_id;
+	assert(dev_id_arr->size == sizeof(dev_id));
+	memcpy(&dev_id, dev_id_arr->data, sizeof(dev_id));
+
+	feedback_data->main_device_id = dev_id;
+
+	drmDevice *device = NULL;
+	if (drmGetDeviceFromDevId(dev_id, 0, &device) != 0) {
+		wlr_log_errno(WLR_ERROR, "drmGetDeviceFromDevId failed");
+		return;
+	}
+
+	const char *name = NULL;
+	if (device->available_nodes & (1 << DRM_NODE_RENDER)) {
+		name = device->nodes[DRM_NODE_RENDER];
+	} else {
+		// Likely a split display/render setup. Pick the primary node and hope
+		// Mesa will open the right render node under-the-hood.
+		assert(device->available_nodes & (1 << DRM_NODE_PRIMARY));
+		name = device->nodes[DRM_NODE_PRIMARY];
+		wlr_log(WLR_DEBUG, "DRM device %s has no render node, "
+			"falling back to primary node", name);
+	}
+
+	feedback_data->backend->drm_render_name = strdup(name);
+
+	drmFreeDevice(&device);
+}
+
+static void linux_dmabuf_feedback_v1_handle_tranche_done(void *data,
+		struct zwp_linux_dmabuf_feedback_v1 *feedback) {
+	struct wlr_wl_linux_dmabuf_feedback_v1 *feedback_data = data;
+	feedback_data->tranche_target_device_id = 0;
+}
+
+static void linux_dmabuf_feedback_v1_handle_tranche_target_device(void *data,
+		struct zwp_linux_dmabuf_feedback_v1 *feedback,
+		struct wl_array *dev_id_arr) {
+	struct wlr_wl_linux_dmabuf_feedback_v1 *feedback_data = data;
+
+	dev_t dev_id;
+	assert(dev_id_arr->size == sizeof(dev_id));
+	memcpy(&dev_id, dev_id_arr->data, sizeof(dev_id));
+
+	feedback_data->tranche_target_device_id = dev_id;
+}
+
+static void linux_dmabuf_feedback_v1_handle_tranche_formats(void *data,
+		struct zwp_linux_dmabuf_feedback_v1 *feedback,
+		struct wl_array *indices_arr) {
+	struct wlr_wl_linux_dmabuf_feedback_v1 *feedback_data = data;
+
+	if (feedback_data->format_table == NULL) {
+		return;
+	}
+	if (feedback_data->tranche_target_device_id != feedback_data->main_device_id) {
+		return;
+	}
+
+	size_t table_cap = feedback_data->format_table_size /
+		sizeof(struct wlr_wl_linux_dmabuf_v1_table_entry);
+	uint16_t *index_ptr;
+	wl_array_for_each(index_ptr, indices_arr) {
+		assert(*index_ptr < table_cap);
+		const struct wlr_wl_linux_dmabuf_v1_table_entry *entry =
+			&feedback_data->format_table[*index_ptr];
+		wlr_drm_format_set_add(&feedback_data->backend->linux_dmabuf_v1_formats,
+			entry->format, entry->modifier);
+	}
+}
+
+static void linux_dmabuf_feedback_v1_handle_tranche_flags(void *data,
+		struct zwp_linux_dmabuf_feedback_v1 *feedback, uint32_t flags) {
+	// TODO: handle SCANOUT flag
+}
+
+static const struct zwp_linux_dmabuf_feedback_v1_listener
+		linux_dmabuf_feedback_v1_listener = {
+	.done = linux_dmabuf_feedback_v1_handle_done,
+	.format_table = linux_dmabuf_feedback_v1_handle_format_table,
+	.main_device = linux_dmabuf_feedback_v1_handle_main_device,
+	.tranche_done = linux_dmabuf_feedback_v1_handle_tranche_done,
+	.tranche_target_device = linux_dmabuf_feedback_v1_handle_tranche_target_device,
+	.tranche_formats = linux_dmabuf_feedback_v1_handle_tranche_formats,
+	.tranche_flags = linux_dmabuf_feedback_v1_handle_tranche_flags,
+};
+
 static bool device_has_name(const drmDevice *device, const char *name) {
 	for (size_t i = 0; i < DRM_NODE_MAX; i++) {
 		if (!(device->available_nodes & (1 << i))) {
@@ -172,8 +302,6 @@ static char *get_render_name(const char *name) {
 static void legacy_drm_handle_device(void *data, struct wl_drm *drm,
 		const char *name) {
 	struct wlr_wl_backend *wl = data;
-
-	// TODO: get FD from linux-dmabuf hints instead
 	wl->drm_render_name = get_render_name(name);
 }
 
@@ -245,7 +373,7 @@ static void registry_global(void *data, struct wl_registry *registry,
 	} else if (strcmp(iface, zwp_linux_dmabuf_v1_interface.name) == 0 &&
 			version >= 3) {
 		wl->zwp_linux_dmabuf_v1 = wl_registry_bind(registry, name,
-			&zwp_linux_dmabuf_v1_interface, 3);
+			&zwp_linux_dmabuf_v1_interface, version >= 4 ? 4 : version);
 		zwp_linux_dmabuf_v1_add_listener(wl->zwp_linux_dmabuf_v1,
 			&linux_dmabuf_v1_listener, wl);
 	} else if (strcmp(iface, zwp_relative_pointer_manager_v1_interface.name) == 0) {
@@ -428,10 +556,9 @@ struct wlr_backend *wlr_wl_backend_create(struct wl_display *display,
 		wlr_log_errno(WLR_ERROR, "Could not obtain reference to remote registry");
 		goto error_display;
 	}
-
 	wl_registry_add_listener(wl->registry, &registry_listener, wl);
+
 	wl_display_roundtrip(wl->remote_display); // get globals
-	wl_display_roundtrip(wl->remote_display); // get linux-dmabuf formats
 
 	if (!wl->compositor) {
 		wlr_log(WLR_ERROR,
@@ -444,6 +571,35 @@ struct wlr_backend *wlr_wl_backend_create(struct wl_display *display,
 		goto error_registry;
 	}
 
+	struct zwp_linux_dmabuf_feedback_v1 *linux_dmabuf_feedback_v1 = NULL;
+	struct wlr_wl_linux_dmabuf_feedback_v1 feedback_data = { .backend = wl };
+	if (wl->zwp_linux_dmabuf_v1 != NULL &&
+			zwp_linux_dmabuf_v1_get_version(wl->zwp_linux_dmabuf_v1) >=
+			ZWP_LINUX_DMABUF_V1_GET_DEFAULT_FEEDBACK_SINCE_VERSION) {
+		linux_dmabuf_feedback_v1 =
+			zwp_linux_dmabuf_v1_get_default_feedback(wl->zwp_linux_dmabuf_v1);
+		if (linux_dmabuf_feedback_v1 == NULL) {
+			wlr_log(WLR_ERROR, "Allocation failed");
+			goto error_registry;
+		}
+		zwp_linux_dmabuf_feedback_v1_add_listener(linux_dmabuf_feedback_v1,
+			&linux_dmabuf_feedback_v1_listener, &feedback_data);
+
+		if (wl->legacy_drm != NULL) {
+			wl_drm_destroy(wl->legacy_drm);
+			wl->legacy_drm = NULL;
+		}
+	}
+
+	wl_display_roundtrip(wl->remote_display); // get linux-dmabuf formats
+
+	if (feedback_data.format_table != NULL) {
+		munmap(feedback_data.format_table, feedback_data.format_table_size);
+	}
+	if (linux_dmabuf_feedback_v1 != NULL) {
+		zwp_linux_dmabuf_feedback_v1_destroy(linux_dmabuf_feedback_v1);
+	}
+
 	struct wl_event_loop *loop = wl_display_get_event_loop(wl->local_display);
 	int fd = wl_display_get_fd(wl->remote_display);
 	wl->remote_display_src = wl_event_loop_add_fd(loop, fd, WL_EVENT_READABLE,

meson.build

@@ -105,7 +105,7 @@ wayland_server = dependency('wayland-server',
 )
 
 drm = dependency('libdrm',
-	version: '>=2.4.108',
+	version: '>=2.4.109',
 	fallback: ['libdrm', 'ext_libdrm'],
 	default_options: [
 		'libkms=false',