s3-prefork: Set up a SIGCHLD handler by default

We need to properly handle preforked children so it is better to just do that
automatically.

If the parent needs/wants to intercept SIGCHLD events it can set a callback
that will be called by the prefork code once the internal cleanup function that
checks all prefork children has been executed.

Signed-off-by: Andreas Schneider <asn@samba.org>

3 files changed, 94 insertions, 52 deletions

diff --git a/source3/lib/server_prefork.c b/source3/lib/server_prefork.c
index ef76a55486..26288f70fd 100644
--- a/source3/lib/server_prefork.c
+++ b/source3/lib/server_prefork.c
@@ -40,9 +40,15 @@ struct prefork_pool {
 	struct pf_worker_data *pool;
 
 	int allowed_clients;
+
+	prefork_sigchld_fn_t *sigchld_fn;
+	void *sigchld_data;
 };
 
-int prefork_pool_destructor(struct prefork_pool *pfp)
+static bool prefork_setup_sigchld_handler(struct tevent_context *ev_ctx,
+					    struct prefork_pool *pfp);
+
+static int prefork_pool_destructor(struct prefork_pool *pfp)
 {
 	munmap(pfp->pool, pfp->pool_size * sizeof(struct pf_worker_data));
 	return 0;
@@ -60,8 +66,9 @@ bool prefork_create_pool(struct tevent_context *ev_ctx, TALLOC_CTX *mem_ctx,
 	size_t data_size;
 	int ret;
 	int i;
+	bool ok;
 
-	pfp = talloc(mem_ctx, struct prefork_pool);
+	pfp = talloc_zero(mem_ctx, struct prefork_pool);
 	if (!pfp) {
 		DEBUG(1, ("Out of memory!\n"));
 		return false;
@@ -124,6 +131,13 @@ bool prefork_create_pool(struct tevent_context *ev_ctx, TALLOC_CTX *mem_ctx,
 		}
 	}
 
+	ok = prefork_setup_sigchld_handler(ev_ctx, pfp);
+	if (!ok) {
+		DEBUG(1, ("Failed to setup SIGCHLD Handler!\n"));
+		talloc_free(pfp);
+		return false;
+	}
+
 	*pf_pool = pfp;
 	return true;
 }
@@ -291,7 +305,7 @@ int prefork_count_active_children(struct prefork_pool *pfp, int *total)
 	return a;
 }
 
-void prefork_cleanup_loop(struct prefork_pool *pfp)
+static void prefork_cleanup_loop(struct prefork_pool *pfp)
 {
 	int status;
 	pid_t pid;
@@ -361,6 +375,46 @@ void prefork_send_signal_to_all(struct prefork_pool *pfp, int signal_num)
 	}
 }
 
+static void prefork_sigchld_handler(struct tevent_context *ev_ctx,
+				    struct tevent_signal *se,
+				    int signum, int count,
+				    void *siginfo, void *pvt)
+{
+	struct prefork_pool *pfp;
+
+	pfp = talloc_get_type_abort(pvt, struct prefork_pool);
+
+	/* run the cleanup function to make sure all dead children are
+	 * properly and timely retired. */
+	prefork_cleanup_loop(pfp);
+
+	if (pfp->sigchld_fn) {
+		pfp->sigchld_fn(ev_ctx, pfp, pfp->sigchld_data);
+	}
+}
+
+static bool prefork_setup_sigchld_handler(struct tevent_context *ev_ctx,
+					  struct prefork_pool *pfp)
+{
+	struct tevent_signal *se;
+
+	se = tevent_add_signal(ev_ctx, pfp, SIGCHLD, 0,
+				prefork_sigchld_handler, pfp);
+	if (!se) {
+		DEBUG(0, ("Failed to setup SIGCHLD handler!\n"));
+		return false;
+	}
+
+	return true;
+}
+
+void prefork_set_sigchld_callback(struct prefork_pool *pfp,
+				  prefork_sigchld_fn_t *sigchld_fn,
+				  void *private_data)
+{
+	pfp->sigchld_fn = sigchld_fn;
+	pfp->sigchld_data = private_data;
+}
 
 /* ==== Functions used by children ==== */
 
diff --git a/source3/lib/server_prefork.h b/source3/lib/server_prefork.h
index f4d03ccca1..c45b96975a 100644
--- a/source3/lib/server_prefork.h
+++ b/source3/lib/server_prefork.h
@@ -21,6 +21,8 @@
 #include "system/network.h"
 #include <tevent.h>
 
+struct prefork_pool;
+
 enum pf_worker_status {
 	PF_WORKER_NONE = 0,
 	PF_WORKER_IDLE,
@@ -76,8 +78,16 @@ typedef int (prefork_main_fn_t)(struct tevent_context *ev,
 				int lock_fd,
 				void *private_data);
 
-struct prefork_pool;
-
+/**
+* @brief Callback function for parents that also want to be called on sigchld
+*
+* @param ev_ctx		The event context
+* @param pool		The pool handler
+* @param private_data	Data private to the parent
+*/
+typedef void (prefork_sigchld_fn_t)(struct tevent_context *ev_ctx,
+				    struct prefork_pool *pool,
+				    void *private_data);
 
 /* ==== Functions used by controlling process ==== */
 
@@ -162,14 +172,6 @@ int prefork_retire_children(struct prefork_pool *pfp,
 int prefork_count_active_children(struct prefork_pool *pfp, int *total);
 
 /**
-* @brief Perform cleanups, like waiting (WNOHANG) dead children.
-*	 MUST be called regularly from the parent main loop.
-*
-* @param pfp	The pool.
-*/
-void prefork_cleanup_loop(struct prefork_pool *pfp);
-
-/**
 * @brief Inform all children that they are allowed to accept 'max' clients
 *	 now. Use this when all children are already busy and more clients
 *	 are trying to connect. It will allow each child to handle more than
@@ -200,6 +202,17 @@ void prefork_reset_allowed_clients(struct prefork_pool *pfp);
 */
 void prefork_send_signal_to_all(struct prefork_pool *pfp, int signal_num);
 
+/**
+* @brief Sets the SIGCHLD callback
+*
+* @param pfp		The pool handler.
+* @param sigchld_fn	The callback function (pass NULL to unset).
+* @param private_data	Private data for the callback function.
+*/
+void prefork_set_sigchld_callback(struct prefork_pool *pfp,
+				  prefork_sigchld_fn_t *sigchld_fn,
+				  void *private_data);
+
 /* ==== Functions used by children ==== */
 
 /**
diff --git a/source3/printing/spoolssd.c b/source3/printing/spoolssd.c
index eb7b5e9b83..107ae58fe4 100644
--- a/source3/printing/spoolssd.c
+++ b/source3/printing/spoolssd.c
@@ -228,7 +228,7 @@ static bool spoolss_shutdown_cb(void *ptr)
 	return true;
 }
 
-/* Childrens */
+/* Children */
 
 struct spoolss_chld_sig_hup_ctx {
 	struct messaging_context *msg_ctx;
@@ -537,21 +537,21 @@ static void check_updater_child(void)
 	}
 }
 
-static void spoolssd_sig_chld_handler(struct tevent_context *ev_ctx,
-				      struct tevent_signal *se,
-				      int signum, int count,
-				      void *siginfo, void *pvt)
+static bool spoolssd_schedule_check(struct tevent_context *ev_ctx,
+				    struct prefork_pool *pfp,
+				    struct timeval current_time);
+static void spoolssd_check_children(struct tevent_context *ev_ctx,
+				    struct tevent_timer *te,
+				    struct timeval current_time,
+				    void *pvt);
+
+static void spoolssd_sigchld_handler(struct tevent_context *ev_ctx,
+				     struct prefork_pool *pfp,
+				     void *private_data)
 {
-	struct prefork_pool *pfp;
 	int active, total;
 	int n, r;
 
-	pfp = talloc_get_type_abort(pvt, struct prefork_pool);
-
-	/* run the cleanup function to make sure all dead children are
-	 * properly and timely retired. */
-	prefork_cleanup_loop(pfp);
-
 	/* now check we do not descend below the minimum */
 	active = prefork_count_active_children(pfp, &total);
 
@@ -574,38 +574,13 @@ static void spoolssd_sig_chld_handler(struct tevent_context *ev_ctx,
 	check_updater_child();
 }
 
-static bool spoolssd_setup_sig_chld_handler(struct tevent_context *ev_ctx,
-					    struct prefork_pool *pfp)
-{
-	struct tevent_signal *se;
-
-	se = tevent_add_signal(ev_ctx, ev_ctx, SIGCHLD, 0,
-				spoolssd_sig_chld_handler, pfp);
-	if (!se) {
-		DEBUG(0, ("Failed to setup SIGCHLD handler!\n"));
-		return false;
-	}
-
-	return true;
-}
-
-static bool spoolssd_schedule_check(struct tevent_context *ev_ctx,
-				    struct prefork_pool *pfp,
-				    struct timeval current_time);
-static void spoolssd_check_children(struct tevent_context *ev_ctx,
-				    struct tevent_timer *te,
-				    struct timeval current_time,
-				    void *pvt);
-
 static bool spoolssd_setup_children_monitor(struct tevent_context *ev_ctx,
 					    struct prefork_pool *pfp)
 {
 	bool ok;
 
-	ok = spoolssd_setup_sig_chld_handler(ev_ctx, pfp);
-	if (!ok) {
-		return false;
-	}
+	/* add our oun sigchld callback */
+	prefork_set_sigchld_callback(pfp, spoolssd_sigchld_handler, NULL);
 
 	ok = spoolssd_schedule_check(ev_ctx, pfp, tevent_timeval_current());
 	return ok;