subd: expose raw API for getting a single fd to a subdaemon.

We're going to use this for the HSM.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/subd.c

@@ -126,12 +126,13 @@ static struct subd_req *get_req(struct subd *sd, int reply_type)
 }
 
 /* We use sockets, not pipes, because fds are bidir. */
-static int subd(const char *dir, const char *name, bool debug,
+static int subd(const char *dir, const char *name, const char *debug_subdaemon,
-		int *msgfd, int dev_disconnect_fd, va_list ap)
+		int *msgfd, int dev_disconnect_fd, va_list *ap)
 {
 	int childmsg[2], execfail[2];
 	pid_t childpid;
 	int err, *fd;
+	bool debug = debug_subdaemon && strends(name, debug_subdaemon);
 
 	if (socketpair(AF_LOCAL, SOCK_STREAM, 0, childmsg) != 0)
 		goto fail;
@@ -169,13 +170,15 @@ static int subd(const char *dir, const char *name, bool debug,
 		}
 
 		/* Dup any extra fds up first. */
-		while ((fd = va_arg(ap, int *)) != NULL) {
+		if (ap) {
+			while ((fd = va_arg(*ap, int *)) != NULL) {
 				/* If this were stdin, dup2 closed! */
 				assert(*fd != STDIN_FILENO);
 				if (!move_fd(*fd, fdnum))
 					goto child_errno_fail;
 				fdnum++;
 			}
+		}
 
 		/* Make (fairly!) sure all other fds are closed. */
 		max = sysconf(_SC_OPEN_MAX);
@@ -201,12 +204,14 @@ static int subd(const char *dir, const char *name, bool debug,
 	close(childmsg[1]);
 	close(execfail[1]);
 
-	while ((fd = va_arg(ap, int *)) != NULL) {
+	if (ap) {
+		while ((fd = va_arg(*ap, int *)) != NULL) {
 			if (taken(fd)) {
 				close(*fd);
 				*fd = -1;
 			}
 		}
+	}
 
 	/* Child will close this without writing on successful exec. */
 	if (read(execfail[0], &err, sizeof(err)) == sizeof(err)) {
@@ -229,6 +234,22 @@ fail:
 	return -1;
 }
 
+int subd_raw(struct lightningd *ld, const char *name)
+{
+	pid_t pid;
+	int msg_fd;
+
+	pid = subd(ld->daemon_dir, name, ld->dev_debug_subdaemon,
+		   &msg_fd, ld->dev_disconnect_fd, NULL);
+	if (pid == (pid_t)-1) {
+		log_unusual(ld->log, "subd %s failed: %s",
+			    name, strerror(errno));
+		return -1;
+	}
+
+	return msg_fd;
+}
+
 static struct io_plan *sd_msg_read(struct io_conn *conn, struct subd *sd);
 
 static struct io_plan *sd_msg_reply(struct io_conn *conn, struct subd *sd,
@@ -394,13 +415,10 @@ struct subd *new_subd(const tal_t *ctx,
 	va_list ap;
 	struct subd *sd = tal(ctx, struct subd);
 	int msg_fd;
-	bool debug;
 
-	debug = ld->dev_debug_subdaemon
-		&& strends(name, ld->dev_debug_subdaemon);
 	va_start(ap, finished);
-	sd->pid = subd(ld->daemon_dir, name, debug, &msg_fd,
+	sd->pid = subd(ld->daemon_dir, name, ld->dev_debug_subdaemon,
-		       ld->dev_disconnect_fd, ap);
+		       &msg_fd, ld->dev_disconnect_fd, &ap);
 	va_end(ap);
 	if (sd->pid == (pid_t)-1) {
 		log_unusual(ld->log, "subd %s failed: %s",

lightningd/subd.h

@@ -74,6 +74,13 @@ struct subd *new_subd(const tal_t *ctx,
 		      int (*msgcb)(struct subd *, const u8 *, const int *fds),
 		      void (*finished)(struct subd *, int), ...);
 
+/**
+ * subd_raw - raw interface to get a subdaemon on an fd (for HSM)
+ * @ld: global state
+ * @name: basename of daemon
+ */
+int subd_raw(struct lightningd *ld, const char *name);
+
 /**
  * subd_send_msg - queue a message to the subdaemon.
  * @sd: subdaemon to request
@@ -82,7 +89,7 @@ struct subd *new_subd(const tal_t *ctx,
 void subd_send_msg(struct subd *sd, const u8 *msg_out);
 
 /**
- * subd_send_msg - queue a file descriptor to pass to the subdaemon.
+ * subd_send_fd - queue a file descriptor to pass to the subdaemon.
  * @sd: subdaemon to request
  * @fd: the file descriptor (closed after passing).
  */