Support older wlr_linux_dmabuf_v1 clients

If a client uses an older version of the dmabuf protocol, use the
`formats` event instead of `modifiers` (since that didn't exist in older
versions).
With a bit of necessary guessing, support dmabuf importing even when
EGL_EXT_image_dma_buf_import_modifiers isn't present instead of
failing up front.

include/wlr/render/dmabuf.h

@@ -16,6 +16,10 @@
 #define DRM_FORMAT_MOD_INVALID ((1ULL<<56) - 1)
 #endif
 
+#ifndef DRM_FORMAT_MOD_LINEAR
+#define DRM_FORMAT_MOD_LINEAR 0
+#endif
+
 #define WLR_DMABUF_MAX_PLANES 4
 
 enum wlr_dmabuf_attributes_flags {

render/egl.c

@@ -3,6 +3,7 @@
 #include <EGL/egl.h>
 #include <EGL/eglext.h>
 #include <stdlib.h>
+#include <drm_fourcc.h>
 #include <wlr/render/egl.h>
 #include <wlr/util/log.h>
 #include "glapi.h"
@@ -382,13 +383,21 @@ EGLImageKHR wlr_egl_create_image_from_wl_drm(struct wlr_egl *egl,
 
 EGLImageKHR wlr_egl_create_image_from_dmabuf(struct wlr_egl *egl,
 		struct wlr_dmabuf_attributes *attributes) {
-	if (!egl->exts.image_base_khr) {
+	if (!egl->exts.image_base_khr || !egl->exts.image_dmabuf_import_ext) {
+		wlr_log(WLR_ERROR, "dmabuf import extension not present");
 		return NULL;
 	}
 
 	bool has_modifier = false;
-	if (attributes->modifier != DRM_FORMAT_MOD_INVALID) {
+
+	// we assume the same way we assumed formats without the import_modifiers
+	// extension that mod_linear is supported. The special mod mod_invalid
+	// is sometimes used to signal modifier unawareness which is what we
+	// have here
+	if (attributes->modifier != DRM_FORMAT_MOD_INVALID &&
+			attributes->modifier != DRM_FORMAT_MOD_LINEAR) {
 		if (!egl->exts.image_dmabuf_import_modifiers_ext) {
+			wlr_log(WLR_ERROR, "dmabuf modifiers extension not present");
 			return NULL;
 		}
 		has_modifier = true;
@@ -460,12 +469,34 @@ EGLImageKHR wlr_egl_create_image_from_dmabuf(struct wlr_egl *egl,
 
 int wlr_egl_get_dmabuf_formats(struct wlr_egl *egl,
 		int **formats) {
-	if (!egl->exts.image_dmabuf_import_ext ||
-			!egl->exts.image_dmabuf_import_modifiers_ext) {
-		wlr_log(WLR_DEBUG, "dmabuf extension not present");
+	if (!egl->exts.image_dmabuf_import_ext) {
+		wlr_log(WLR_DEBUG, "dmabuf import extension not present");
 		return -1;
 	}
 
+	// when we only have the image_dmabuf_import extension we can't query
+	// which formats are supported. These two are on almost always
+	// supported; it's the intended way to just try to create buffers.
+	// Just a guess but better than not supporting dmabufs at all,
+	// given that the modifiers extension isn't supported everywhere.
+	if (!egl->exts.image_dmabuf_import_modifiers_ext) {
+		static const int fallback_formats[] = {
+			DRM_FORMAT_ARGB8888,
+			DRM_FORMAT_XRGB8888,
+		};
+		static unsigned num = sizeof(fallback_formats) /
+			sizeof(fallback_formats[0]);
+
+		*formats = calloc(num, sizeof(int));
+		if (!*formats) {
+			wlr_log_errno(WLR_ERROR, "Allocation failed");
+			return -1;
+		}
+
+		memcpy(*formats, fallback_formats, num * sizeof(**formats));
+		return num;
+	}
+
 	EGLint num;
 	if (!eglQueryDmaBufFormatsEXT(egl->display, 0, NULL, &num)) {
 		wlr_log(WLR_ERROR, "failed to query number of dmabuf formats");
@@ -488,12 +519,16 @@ int wlr_egl_get_dmabuf_formats(struct wlr_egl *egl,
 
 int wlr_egl_get_dmabuf_modifiers(struct wlr_egl *egl,
 		int format, uint64_t **modifiers) {
-	if (!egl->exts.image_dmabuf_import_ext ||
-			!egl->exts.image_dmabuf_import_modifiers_ext) {
+	if (!egl->exts.image_dmabuf_import_ext) {
 		wlr_log(WLR_DEBUG, "dmabuf extension not present");
 		return -1;
 	}
 
+	if(!egl->exts.image_dmabuf_import_modifiers_ext) {
+		*modifiers = NULL;
+		return 0;
+	}
+
 	EGLint num;
 	if (!eglQueryDmaBufModifiersEXT(egl->display, format, 0,
 			NULL, NULL, &num)) {

types/wlr_linux_dmabuf_v1.c

@@ -103,6 +103,7 @@ static void params_add(struct wl_client *client,
 		close(fd);
 		return;
 	}
+
 	buffer->attributes.modifier = modifier;
 	buffer->has_modifier = true;
 
@@ -382,13 +383,9 @@ struct wlr_linux_dmabuf_v1 *wlr_linux_dmabuf_v1_from_resource(
 	return dmabuf;
 }
 
-static void linux_dmabuf_send_modifiers(struct wlr_linux_dmabuf_v1 *linux_dmabuf,
-		struct wl_resource *resource) {
+static void linux_dmabuf_send_formats(struct wlr_linux_dmabuf_v1 *linux_dmabuf,
+		struct wl_resource *resource, uint32_t version) {
 	struct wlr_renderer *renderer = linux_dmabuf->renderer;
-	/*
-	 * Use EGL_EXT_image_dma_buf_import_modifiers to query and advertise
-	 * format/modifier codes.
-	 */
 	uint64_t modifier_invalid = DRM_FORMAT_MOD_INVALID;
 	int *formats = NULL;
 	int num_formats = wlr_renderer_get_dmabuf_formats(renderer, &formats);
@@ -410,10 +407,17 @@ static void linux_dmabuf_send_modifiers(struct wlr_linux_dmabuf_v1 *linux_dmabuf
 			modifiers = &modifier_invalid;
 		}
 		for (int j = 0; j < num_modifiers; j++) {
+			if (version >= ZWP_LINUX_DMABUF_V1_MODIFIER_SINCE_VERSION) {
 				uint32_t modifier_lo = modifiers[j] & 0xFFFFFFFF;
 				uint32_t modifier_hi = modifiers[j] >> 32;
-			zwp_linux_dmabuf_v1_send_modifier(resource, formats[i],
-				modifier_hi, modifier_lo);
+				zwp_linux_dmabuf_v1_send_modifier(resource,
+					formats[i],
+					modifier_hi,
+					modifier_lo);
+			} else if (modifiers[j] == DRM_FORMAT_MOD_LINEAR ||
+				   modifiers == &modifier_invalid) {
+				zwp_linux_dmabuf_v1_send_format(resource, formats[i]);
+			}
 		}
 		if (modifiers != &modifier_invalid) {
 			free(modifiers);
@@ -439,10 +443,7 @@ static void linux_dmabuf_bind(struct wl_client *client, void *data,
 	wl_resource_set_implementation(resource, &linux_dmabuf_impl,
 		linux_dmabuf, linux_dmabuf_resource_destroy);
 	wl_list_insert(&linux_dmabuf->resources, wl_resource_get_link(resource));
-
-	if (version >= ZWP_LINUX_DMABUF_V1_MODIFIER_SINCE_VERSION) {
-		linux_dmabuf_send_modifiers(linux_dmabuf, resource);
-	}
+	linux_dmabuf_send_formats(linux_dmabuf, resource, version);
 }
 
 void wlr_linux_dmabuf_v1_destroy(struct wlr_linux_dmabuf_v1 *linux_dmabuf) {