Make libcap optional.

CMakeLists.txt

@@ -50,7 +50,7 @@ find_package(GBM REQUIRED)
 find_package(LibInput REQUIRED)
 find_package(XKBCommon REQUIRED)
 find_package(Udev REQUIRED)
-find_package(Libcap REQUIRED)
+find_package(Libcap)
 find_package(Systemd)
 
 include(Wayland)

README.md

@@ -18,6 +18,7 @@ Install dependencies:
 * libinput
 * udev
 * systemd (optional, for logind support)
+* libcap (optional, for capability support)
 * asciidoc (optional, for man pages)
 
 Run these commands:

session/CMakeLists.txt

@@ -1,7 +1,6 @@
 include_directories(
     ${WAYLAND_INCLUDE_DIR}
     ${DRM_INCLUDE_DIRS}
-    ${Libcap_INCLUDE_DIRS}
 )
 
 set(sources
@@ -12,7 +11,6 @@ set(sources
 set(libs
     wlr-util
     ${WAYLAND_LIBRARIES}
-    ${Libcap_LIBRARIES}
 )
 
 if (SYSTEMD_FOUND)
@@ -24,5 +22,13 @@ if (SYSTEMD_FOUND)
     list(APPEND libs ${SYSTEMD_LIBRARIES})
 endif ()
 
+if (Libcap_FOUND)
+    add_definitions(${Libcap_DEFINITIONS})
+    include_directories(${Libcap_INCLUDE_DIRS})
+
+    add_definitions(-DHAS_LIBCAP)
+    list(APPEND libs ${Libcap_LIBRARIES})
+endif ()
+
 add_library(wlr-session ${sources})
 target_link_libraries(wlr-session ${libs})

session/direct.c

@@ -321,17 +321,35 @@ static void communicate(int sock) {
 
 }
 
-static struct wlr_session *direct_session_start(struct wl_display *disp) {
+#ifdef HAS_LIBCAP
+static bool have_permissions(void) {
 	cap_t cap = cap_get_proc();
 	cap_flag_value_t val;
 
 	if (!cap || cap_get_flag(cap, CAP_SYS_ADMIN, CAP_PERMITTED, &val) || val != CAP_SET) {
 		wlr_log(L_ERROR, "Do not have CAP_SYS_ADMIN; cannot become DRM master");
 		cap_free(cap);
-		return NULL;
+		return false;
 	}
 
 	cap_free(cap);
+	return true;
+}
+#else
+static bool have_permissions(void) {
+	if (geteuid() != 0) {
+		wlr_log(L_ERROR, "Do not have root privileges; cannot become DRM master");
+		return false;
+	}
+
+	return true;
+}
+#endif
+
+static struct wlr_session *direct_session_start(struct wl_display *disp) {
+	if (!have_permissions()) {
+		return NULL;
+	}
 
 	int sock[2];
 	if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sock) < 0) {