extend the API to export frame buffers using DRM PRIME file descriptors

Export frame buffers, providing applications like those based on libegt
with DRM PRIME file descriptors. Hence applications can next pass these
DRM PRIME file descriptors down to libm2d, which finally use them to
import the frame buffers created by libplanes so the GPU can ultimately
render into these frame buffers.

Signed-off-by: Cyrille Pitchen <[email protected]>
Signed-off-by: Ludovic Desroches <[email protected]>

include/planes/kms.h

@@ -83,6 +83,8 @@ struct kms_framebuffer {
 	uint32_t handle;
 	uint32_t id;
 
+	int prime_fd;
+
 	void *ptr;
 };
 

include/planes/plane.h

@@ -62,6 +62,8 @@ struct plane_data
 	struct kms_framebuffer** fbs;
 	/** The framebuffer.  Must call plane_map() to allocate this. */
 	void** bufs;
+	/** The DRM PRIME file descriptor. Must call plane_fb_export() to set this. */
+	int* prime_fds;
 	unsigned int front_buf;
 	/** The number of framebuffers. */
 	uint32_t buffer_count;
@@ -376,6 +378,23 @@ int plane_fb_map(struct plane_data* plane);
  */
 void plane_fb_unmap(struct plane_data* plane);
 
+/**
+ * Export the framebuffer using a DRM PRIME file descriptor.
+ *
+ * @param plane The plane.
+ */
+int plane_fb_export(struct plane_data* plane);
+
+/**
+ * Opposite of plane_fb_export().
+ *
+ * @param plane The plane.
+ *
+ * @note Like plane_fb_unmap(), plane_fb_unexport() is automatically called from
+ * plane_free() through plane_fb_free().
+ */
+void plane_fb_unexport(struct plane_data* plane);
+
 /**
  * Reallocate the framebuffer to the specified height, width, and format.
  *

src/kms-framebuffer.c

@@ -78,6 +78,7 @@ struct kms_framebuffer *kms_framebuffer_create(struct kms_device *device,
 	fb->width = width;
 	fb->height = height;
 	fb->format = format;
+	fb->prime_fd = -1;
 
 	memset(&args, 0, sizeof(args));
 	args.width = width;
@@ -244,3 +245,26 @@ void kms_framebuffer_unmap(struct kms_framebuffer *fb)
 		fb->ptr = NULL;
 	}
 }
+
+int kms_framebuffer_export(struct kms_framebuffer *fb, int *prime_fd)
+{
+	struct kms_device *device = fb->device;
+	struct drm_prime_handle args;
+	int err;
+
+	if (fb->prime_fd != -1) {
+		*prime_fd = fb->prime_fd;
+		return 0;
+	}
+
+	memset(&args, 0, sizeof(args));
+	args.handle = fb->handle;
+
+	err = drmIoctl(device->fd, DRM_IOCTL_PRIME_HANDLE_TO_FD, &args);
+	if (err < 0)
+		return -errno;
+
+	*prime_fd = fb->prime_fd = args.fd;
+
+	return 0;
+}

src/p_kms.h

@@ -57,6 +57,7 @@ struct kms_framebuffer *kms_framebuffer_create(struct kms_device *device,
 void kms_framebuffer_free(struct kms_framebuffer *fb);
 int kms_framebuffer_map(struct kms_framebuffer *fb, void **ptrp);
 void kms_framebuffer_unmap(struct kms_framebuffer *fb);
+int kms_framebuffer_export(struct kms_framebuffer *fb, int *prime_fd);
 
 struct kms_screen *kms_screen_create(struct kms_device *device, uint32_t id);
 void kms_screen_free(struct kms_screen *screen);

src/plane.c

@@ -90,9 +90,10 @@ struct plane_data* plane_create_buffered(struct kms_device* device, int type,
 
 	plane->fbs = calloc(buffer_count, sizeof(struct kms_framebuffer*));
 	plane->bufs = calloc(buffer_count, sizeof(void*));
+	plane->prime_fds = calloc(buffer_count, sizeof(int));
 	plane->gem_names = calloc(buffer_count, sizeof(uint32_t*));
 
-	if (!plane->fbs || !plane->bufs || !plane->gem_names) {
+	if (!plane->fbs || !plane->bufs || !plane->prime_fds || !plane->gem_names) {
 		LOG("error: failed to allocate plane\n");
 		goto abort;
 	}
@@ -137,6 +138,7 @@ struct plane_data* plane_create_buffered(struct kms_device* device, int type,
 				goto abort;
 			}
 		}
+		plane->prime_fds[fb] = -1;
 	}
 
 	plane->index = index;
@@ -168,6 +170,7 @@ static void plane_fb_free(struct plane_data* plane)
 	uint32_t fb;
 
 	plane_fb_unmap(plane);
+	plane_fb_unexport(plane);
 
 	for (fb = 0; fb < plane->buffer_count; fb++) {
 		if (plane->fbs[fb]) {
@@ -186,6 +189,8 @@ void plane_free(struct plane_data* plane)
 			free(plane->fbs);
 		if (plane->bufs)
 			free(plane->bufs);
+		if (plane->prime_fds)
+			free(plane->prime_fds);
 		if (plane->gem_names)
 			free(plane->gem_names);
 		free(plane);
@@ -465,6 +470,35 @@ void plane_fb_unmap(struct plane_data* plane)
 	}
 }
 
+int plane_fb_export(struct plane_data* plane)
+{
+	uint32_t fb;
+
+	for (fb = 0; fb < plane->buffer_count; fb++) {
+		if (plane->prime_fds[fb] == -1) {
+			int err;
+
+			err = kms_framebuffer_export(plane->fbs[fb], &plane->prime_fds[fb]);
+			if (err < 0)
+			{
+				LOG("error: kms_framebuffer_export() failed: %s\n",
+				    strerror(-err));
+				return err;
+			}
+		}
+	}
+
+	return 0;
+}
+
+void plane_fb_unexport(struct plane_data* plane)
+{
+	uint32_t fb;
+
+	for (fb = 0; fb < plane->buffer_count; fb++)
+		plane->prime_fds[fb] = -1;
+}
+
 int plane_flip(struct plane_data* plane, uint32_t target)
 {
 	plane->front_buf = target;