Add option to specify pid file

Closes #969

lightningd/lightningd.c

@@ -13,6 +13,7 @@
 #include <ccan/io/io.h>
 #include <ccan/noerr/noerr.h>
 #include <ccan/pipecmd/pipecmd.h>
+#include <ccan/read_write_all/read_write_all.h>
 #include <ccan/take/take.h>
 #include <ccan/tal/grab_file/grab_file.h>
 #include <ccan/tal/path/path.h>
@@ -24,6 +25,7 @@
 #include <common/version.h>
 #include <common/wireaddr.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <lightningd/bitcoind.h>
 #include <lightningd/chaintopology.h>
 #include <lightningd/invoice.h>
@@ -39,6 +41,8 @@ char *bitcoin_datadir;
 
 struct backtrace_state *backtrace_state;
 
+int pid_fd;
+
 static struct lightningd *new_lightningd(const tal_t *ctx)
 {
 	struct lightningd *ld = tal(ctx, struct lightningd);
@@ -70,6 +74,7 @@ static struct lightningd *new_lightningd(const tal_t *ctx)
 	ld->topology = new_topology(ld, ld->log);
 	ld->debug_subdaemon_io = NULL;
 	ld->daemon = false;
+	ld->pidfile = NULL;
 
 	return ld;
 }
@@ -250,6 +255,28 @@ static void daemonize_but_keep_dir(void)
 	tal_free(cwd);
 }
 
+static void pidfile_create(const struct lightningd *ld)
+{
+	char *pid;
+	const tal_t *tmpctx = tal_tmpctx(NULL);
+
+	/* Create PID file */
+	pid_fd = open(ld->pidfile, O_WRONLY|O_CREAT, 0640);
+	if (pid_fd < 0)
+		err(1, "Failed to open PID file");
+
+	/* Lock PID file */
+	if (lockf(pid_fd, F_TLOCK, 0) < 0)
+		/* Problem locking file */
+		err(1, "lightningd already running? Error locking PID file");
+
+	/* Get current PID and write to PID fie */
+	pid = tal_fmt(tmpctx, "%d\n", getpid());
+	write_all(pid_fd, pid, strlen(pid));
+
+	tal_free(tmpctx);
+}
+
 int main(int argc, char *argv[])
 {
 	struct lightningd *ld;
@@ -280,6 +307,9 @@ int main(int argc, char *argv[])
 	/* Handle options and config; move to .lightningd */
 	newdir = handle_opts(ld, argc, argv);
 
+	/* Create PID file */
+	pidfile_create(ld);
+
 	/* Ignore SIGPIPE: we look at our write return values*/
 	signal(SIGPIPE, SIG_IGN);
 
@@ -384,6 +414,8 @@ int main(int argc, char *argv[])
 	}
 
 	shutdown_subdaemons(ld);
+	close(pid_fd);
+	remove(ld->pidfile);
 
 	tal_free(ld);
 	opt_free_table();

lightningd/lightningd.h

@@ -142,6 +142,9 @@ struct lightningd {
 	/* Transaction filter matching what we're interested in */
 	struct txfilter *owned_txfilter;
 
+	/* PID file */
+	char *pidfile;
+
 	/* May be useful for non-developers debugging in the field */
 	char *debug_subdaemon_io;
 

lightningd/options.c

@@ -449,6 +449,10 @@ static void setup_default_config(struct lightningd *ld)
 		ld->config = testnet_config;
 	else
 		ld->config = mainnet_config;
+
+	/* Set default PID file name to be per-network */
+	tal_free(ld->pidfile);
+	ld->pidfile = tal_fmt(ld, "lightningd-%s.pid", get_chainparams(ld)->network_name);
 }
 
 
@@ -560,6 +564,9 @@ void register_opts(struct lightningd *ld)
 	opt_register_arg("--bitcoin-rpcconnect", opt_set_talstr, NULL,
 			 &ld->topology->bitcoind->rpcconnect,
 			 "bitcoind RPC host to connect to");
+	opt_register_arg("--pid-file=<file>", opt_set_talstr, opt_show_charp,
+			 &ld->pidfile,
+			 "Specify pid file");
 
 	opt_register_arg(
 	    "--channel-update-interval=<s>", opt_set_u32, opt_show_u32,