ctdb-common: Add support for sock daemon to notify of successful startup

The daemon writes 0 into the specified file descriptor when it is up
and listening.  This can be used to avoid loops in clients that
attempt to connect until they succeed.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13592

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
(cherry picked from commit dc6040c121c65d5551c686f3f1be2891795f48aa)

2 files changed, 36 insertions, 0 deletions

diff --git a/ctdb/common/sock_daemon.c b/ctdb/common/sock_daemon.c
index 7554cd6da07..03d3ac1f1ec 100644
--- a/ctdb/common/sock_daemon.c
+++ b/ctdb/common/sock_daemon.c
@@ -31,6 +31,7 @@
 #include "lib/util/dlinklist.h"
 #include "lib/util/tevent_unix.h"
 #include "lib/util/become_daemon.h"
+#include "lib/util/sys_rw.h"
 
 #include "common/logging.h"
 #include "common/reqid.h"
@@ -71,6 +72,7 @@ struct sock_daemon_context {
 
 	struct pidfile_context *pid_ctx;
 	struct sock_socket *socket_list;
+	int startup_fd;
 };
 
 /*
@@ -483,6 +485,7 @@ int sock_daemon_setup(TALLOC_CTX *mem_ctx, const char *daemon_name,
 
 	sockd->funcs = funcs;
 	sockd->private_data = private_data;
+	sockd->startup_fd = -1;
 
 	ret = logging_init(sockd, logging, debug_level, daemon_name);
 	if (ret != 0) {
@@ -514,6 +517,11 @@ int sock_daemon_add_unix(struct sock_daemon_context *sockd,
 	return 0;
 }
 
+void sock_daemon_set_startup_fd(struct sock_daemon_context *sockd, int fd)
+{
+	sockd->startup_fd = fd;
+}
+
 /*
  * Run socket daemon
  */
@@ -543,6 +551,7 @@ static void sock_daemon_run_socket_fail(struct tevent_req *subreq);
 static void sock_daemon_run_watch_pid(struct tevent_req *subreq);
 static void sock_daemon_run_wait(struct tevent_req *req);
 static void sock_daemon_run_wait_done(struct tevent_req *subreq);
+static void sock_daemon_startup_notify(struct sock_daemon_context *sockd);
 
 struct tevent_req *sock_daemon_run_send(TALLOC_CTX *mem_ctx,
 					struct tevent_context *ev,
@@ -669,6 +678,8 @@ static void sock_daemon_run_started(struct tevent_req *subreq)
 		return;
 	}
 	sock_daemon_run_wait(req);
+
+	sock_daemon_startup_notify(sockd);
 }
 
 static void sock_daemon_run_startup_done(struct tevent_req *subreq)
@@ -696,6 +707,8 @@ static void sock_daemon_run_startup_done(struct tevent_req *subreq)
 		return;
 	}
 	sock_daemon_run_wait(req);
+
+	sock_daemon_startup_notify(sockd);
 }
 
 static void sock_daemon_run_signal_handler(struct tevent_context *ev,
@@ -961,6 +974,19 @@ static void sock_daemon_run_wait_done(struct tevent_req *subreq)
 	sock_daemon_run_shutdown(req);
 }
 
+static void sock_daemon_startup_notify(struct sock_daemon_context *sockd)
+{
+	if (sockd->startup_fd != -1) {
+		unsigned int zero = 0;
+		ssize_t num;
+
+		num = sys_write(sockd->startup_fd, &zero, sizeof(zero));
+		if (num != sizeof(zero)) {
+			D_WARNING("Failed to write zero to pipe FD\n");
+		}
+	}
+}
+
 bool sock_daemon_run_recv(struct tevent_req *req, int *perr)
 {
 	int ret;
diff --git a/ctdb/common/sock_daemon.h b/ctdb/common/sock_daemon.h
index a071833c2f3..a28f8c6f39c 100644
--- a/ctdb/common/sock_daemon.h
+++ b/ctdb/common/sock_daemon.h
@@ -208,6 +208,16 @@ int sock_daemon_add_unix(struct sock_daemon_context *sockd,
 			 void *private_data);
 
 /**
+ * @brief Set file descriptor for indicating startup success
+ *
+ * On successful completion, 0 (unsigned int) will be written to the fd.
+ *
+ * @param[in] sockd Socket daemon context
+ * @param[in] fd File descriptor
+ */
+void sock_daemon_set_startup_fd(struct sock_daemon_context *sockd, int fd);
+
+/**
  * @brief Async computation start to run a socket daemon
  *
  * @param[in] mem_ctx Talloc memory context