From 94ed8f9496b11cb084a1d4f83e13fc910f52033f Mon Sep 17 00:00:00 2001
From: Simon Zeni <simon@bl4ckb0ne.ca>
Date: Tue, 25 May 2021 19:23:10 -0400
Subject: [PATCH] backend/drm: introduce wlr_drm_backend_get_non_master_fd

---
 backend/drm/drm.c         | 26 ++++++++++++++++++++++++++
 include/wlr/backend/drm.h |  7 +++++++
 2 files changed, 33 insertions(+)

diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index e9842bb3..0e981d59 100644
--- a/backend/drm/drm.c
+++ b/backend/drm/drm.c
@@ -3,6 +3,7 @@
 #include <drm_fourcc.h>
 #include <drm_mode.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <inttypes.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -1479,6 +1480,31 @@ void destroy_drm_connector(struct wlr_drm_connector *conn) {
 	free(conn);
 }
 
+int wlr_drm_backend_get_non_master_fd(struct wlr_backend *backend) {
+	assert(backend);
+
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
+	char *path = drmGetDeviceNameFromFd2(drm->fd);
+	if (!path) {
+		wlr_log(WLR_ERROR, "Failed to get device name from DRM fd");
+		return -1;
+	}
+
+	int fd = open(path, O_RDWR | O_CLOEXEC);
+	if (fd < 0) {
+		wlr_log_errno(WLR_ERROR, "Unable to clone DRM fd for client fd");
+		free(path);
+		return -1;
+	}
+
+	if (drmIsMaster(fd) && drmDropMaster(fd) < 0) {
+		wlr_log_errno(WLR_ERROR, "Failed to drop master");
+		return -1;
+	}
+
+	return fd;
+}
+
 /* TODO: make the function return a `wlr_drm_lease` to provide a destroy event
  * that can be fired when the kernel notifies us through uevent that the lease
  * has been destroyed
diff --git a/include/wlr/backend/drm.h b/include/wlr/backend/drm.h
index c5351d65..0d8c51e0 100644
--- a/include/wlr/backend/drm.h
+++ b/include/wlr/backend/drm.h
@@ -33,6 +33,13 @@ bool wlr_output_is_drm(struct wlr_output *output);
  */
 uint32_t wlr_drm_connector_get_id(struct wlr_output *output);
 
+/**
+ * Tries to open non-master DRM FD. The compositor must not call `drmSetMaster`
+ * on the returned FD.
+ * Returns a valid opened DRM FD, or -1 on error.
+ */
+int wlr_drm_backend_get_non_master_fd(struct wlr_backend *backend);
+
 /**
  * Leases a given output to the caller. The output must be from the associated
  * DRM backend.