meson: Make default seatd socket path configurable

FreeBSD and Linux have different preferred socket locations. Expose an
option to set the location, and implement simple auto-logic for
linux/freebsd.

libseat/backend/seatd.c

@@ -67,9 +67,9 @@ static int seatd_connect(void) {
 		close(fd);
 		return -1;
 	}
-	char *path = getenv("SEATD_SOCK");
+	const char *path = getenv("SEATD_SOCK");
 	if (path == NULL) {
-		path = "/run/seatd.sock";
+		path = SEATD_DEFAULTPATH;
 	}
 	addr.unix.sun_family = AF_UNIX;
 	strncpy(addr.unix.sun_path, path, sizeof addr.unix.sun_path);

meson.build

@@ -14,6 +14,16 @@ project(
 # Bump whenever ABI-breaking changes occur.
 libseat_soversion = 1
 
+defaultpath = get_option('defaultpath')
+if defaultpath == ''
+	system = target_machine.system()
+	if system == 'linux'
+		defaultpath = '/run/seatd.sock'
+	else
+		defaultpath = '/var/run/seatd.sock'
+	endif
+endif
+
 add_project_arguments(
 	[
 		'-Wundef',
@@ -32,6 +42,7 @@ add_project_arguments(
 		'-D_XOPEN_SOURCE=700',
 		'-D__BSD_VISIBLE',
 		'-DSEATD_VERSION="@0@"'.format(meson.project_version()),
+		'-DSEATD_DEFAULTPATH="@0@"'.format(defaultpath)
 	],
 	language: 'c',
 )

meson_options.txt

@@ -4,4 +4,4 @@ option('builtin', type: 'feature', value: 'disabled', description: 'builtin seat
 option('server', type: 'feature', value: 'enabled', description: 'seatd server')
 option('examples', type: 'feature', value: 'enabled', description: 'libseat example programs')
 option('man-pages', type: 'feature', value: 'auto', description: 'Generate and install man pages')
-
+option('defaultpath', type: 'string', value: '', description: 'Default location for seatd socket (empty for default)')

seatd/seatd.c

@@ -17,7 +17,7 @@
 
 #define LISTEN_BACKLOG 16
 
-static int open_socket(char *path, int uid, int gid) {
+static int open_socket(const char *path, int uid, int gid) {
 	union {
 		struct sockaddr_un unix;
 		struct sockaddr generic;
@@ -78,7 +78,7 @@ int main(int argc, char *argv[]) {
 
 	int c;
 	int uid = 0, gid = 0;
-	char *socket_path = getenv("SEATD_SOCK");
+	const char *socket_path = getenv("SEATD_SOCK");
 	while ((c = getopt(argc, argv, "vhs:g:u:")) != -1) {
 		switch (c) {
 		case 's':
@@ -119,7 +119,7 @@ int main(int argc, char *argv[]) {
 	}
 
 	if (socket_path == NULL) {
-		socket_path = "/run/seatd.sock";
+		socket_path = SEATD_DEFAULTPATH;
 		struct stat st;
 		if (stat(socket_path, &st) == 0) {
 			log_info("removing leftover seatd socket");