render/dmabuf: add dmabuf_export_sync_file()

include/render/dmabuf.h

@@ -23,4 +23,13 @@ bool dmabuf_check_sync_file_import_export(void);
  */
 bool dmabuf_import_sync_file(int dmabuf_fd, uint32_t flags, int sync_file_fd);
 
+/**
+ * Export a sync_file from a DMA-BUF with DMA_BUF_IOCTL_EXPORT_SYNC_FILE.
+ *
+ * The sync_file FD is returned on success, -1 is returned on error.
+ *
+ * This can be used to make explicit sync interoperate with implicit sync.
+ */
+int dmabuf_export_sync_file(int dmabuf_fd, uint32_t flags);
+
 #endif

render/dmabuf_fallback.c

@@ -10,3 +10,8 @@ bool dmabuf_import_sync_file(int dmabuf_fd, uint32_t flags, int sync_file_fd) {
 	wlr_log(WLR_ERROR, "DMA-BUF sync_file import IOCTL not available on this system");
 	return false;
 }
+
+int dmabuf_export_sync_file(int dmabuf_fd, uint32_t flags) {
+	wlr_log(WLR_ERROR, "DMA-BUF sync_file export IOCTL not available on this system");
+	return false;
+}

render/dmabuf_linux.c

@@ -51,6 +51,7 @@ bool dmabuf_check_sync_file_import_export(void) {
 }
 
 // TODO: drop these definitions once widespread
+
 #if !defined(DMA_BUF_IOCTL_IMPORT_SYNC_FILE)
 
 struct dma_buf_import_sync_file {
@@ -62,6 +63,17 @@ struct dma_buf_import_sync_file {
 
 #endif
 
+#if !defined(DMA_BUF_IOCTL_EXPORT_SYNC_FILE)
+
+struct dma_buf_export_sync_file {
+	__u32 flags;
+	__s32 fd;
+};
+
+#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE _IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
+
+#endif
+
 bool dmabuf_import_sync_file(int dmabuf_fd, uint32_t flags, int sync_file_fd) {
 	struct dma_buf_import_sync_file data = {
 		.flags = flags,
@@ -73,3 +85,15 @@ bool dmabuf_import_sync_file(int dmabuf_fd, uint32_t flags, int sync_file_fd) {
 	}
 	return true;
 }
+
+int dmabuf_export_sync_file(int dmabuf_fd, uint32_t flags) {
+	struct dma_buf_export_sync_file data = {
+		.flags = flags,
+		.fd = -1,
+	};
+	if (drmIoctl(dmabuf_fd, DMA_BUF_IOCTL_EXPORT_SYNC_FILE, &data) != 0) {
+		wlr_log_errno(WLR_ERROR, "drmIoctl(EXPORT_SYNC_FILE) failed");
+		return -1;
+	}
+	return data.fd;
+}