introduce a sync API

src/lxc/Makefile.am

@@ -31,6 +31,7 @@ liblxc_so_SOURCES = \
 	cgroup.c cgroup.h \
 	lxc.h \
 	utils.c utils.h \
+	sync.c sync.h \
 	namespace.h namespace.c \
 	conf.c conf.h \
 	confile.c confile.h \

src/lxc/start.c

@@ -124,6 +124,7 @@ int signalfd(int fd, const sigset_t *mask, int flags)
 #include "monitor.h"
 #include "commands.h"
 #include "console.h"
+#include "sync.h"
 
 lxc_log_define(lxc_start, lxc);
 
@@ -414,29 +415,19 @@ void lxc_abort(const char *name, struct lxc_handler *handler)
 static int do_start(void *data)
 {
 	struct lxc_handler *handler = data;
-	int err = -1, sync;
 
 	if (sigprocmask(SIG_SETMASK, &handler->oldmask, NULL)) {
 		SYSERROR("failed to set sigprocmask");
 		return -1;
 	}
 
-	close(handler->sv[1]);
+	lxc_sync_fini_parent(handler);
 
-	/* Be sure we don't inherit this after the exec */
-	fcntl(handler->sv[0], F_SETFD, FD_CLOEXEC);
-
-	/* Tell our father he can begin to configure the container */
-	if (write(handler->sv[0], &sync, sizeof(sync)) < 0) {
-		SYSERROR("failed to write socket");
-		return -1;
-	}
-
-	/* Wait for the father to finish the configuration */
-	if (read(handler->sv[0], &sync, sizeof(sync)) < 0) {
-		SYSERROR("failed to read socket");
+	/* Tell the parent task it can begin to configure the
+	 * container and wait for it to finish
+	 */
+	if (lxc_sync_barrier_parent(handler, LXC_SYNC_CONFIGURE))
 		return -1;
-	}
 
 	/* Setup the container, ip, names, utsname, ... */
 	if (lxc_setup(handler->name, handler->conf)) {
@@ -462,24 +453,18 @@ static int do_start(void *data)
 		return -1;
 
 out_warn_father:
-	/* If the exec fails, tell that to our father */
-	if (write(handler->sv[0], &err, sizeof(err)) < 0)
-		SYSERROR("failed to write the socket");
+	lxc_sync_wake_parent(handler, LXC_SYNC_POST_CONFIGURE);
 	return -1;
 }
 
 int lxc_spawn(struct lxc_handler *handler)
 {
 	int clone_flags;
-	int sync;
 	int failed_before_rename = 0;
 	const char *name = handler->name;
 
-	/* Synchro socketpair */
-	if (socketpair(AF_LOCAL, SOCK_STREAM, 0, handler->sv)) {
-		SYSERROR("failed to create communication socketpair");
+	if (lxc_sync_init(handler))
 		return -1;
-	}
 
 	clone_flags = CLONE_NEWUTS|CLONE_NEWPID|CLONE_NEWIPC|CLONE_NEWNS;
 	if (!lxc_list_empty(&handler->conf->network)) {
@@ -491,8 +476,7 @@ int lxc_spawn(struct lxc_handler *handler)
 		 */
 		if (lxc_create_network(&handler->conf->network)) {
 			ERROR("failed to create the network");
-			close(handler->sv[0]);
-			close(handler->sv[1]);
+			lxc_sync_fini(handler);
 			return -1;
 		}
 	}
@@ -505,13 +489,10 @@ int lxc_spawn(struct lxc_handler *handler)
 		goto out_delete_net;
 	}
 
-	close(handler->sv[0]);
-	
-	/* Wait for the child to be ready */
-	if (read(handler->sv[1], &sync, sizeof(sync)) <= 0) {
-		ERROR("sync read failure : %m");
+	lxc_sync_fini_child(handler);
+
+	if (lxc_sync_wait_child(handler, LXC_SYNC_CONFIGURE))
 		failed_before_rename = 1;
-	}
 
 	if (lxc_rename_nsgroup(name, handler))
 		goto out_delete_net;
@@ -527,17 +508,11 @@ int lxc_spawn(struct lxc_handler *handler)
 		}
 	}
 
-	/* Tell the child to continue its initialization */
-	if (write(handler->sv[1], &sync, sizeof(sync)) < 0) {
-		SYSERROR("failed to write the socket");
-		goto out_abort;
-	}
-
-	/* Wait for the child to exec or returning an error */
-	if (read(handler->sv[1], &sync, sizeof(sync)) < 0) {
-		ERROR("failed to read the socket");
-		goto out_abort;
-	}
+	/* Tell the child to continue its initialization and wait for
+	 * it to exec or return an error
+	 */
+	if (lxc_sync_barrier_child(handler, LXC_SYNC_POST_CONFIGURE))
+		return -1;
 
 	if (handler->ops->post_start(handler, handler->data))
 		goto out_abort;
@@ -548,7 +523,7 @@ int lxc_spawn(struct lxc_handler *handler)
 		goto out_abort;
 	}
 
-	close(handler->sv[1]);
+	lxc_sync_fini(handler);
 	return 0;
 
 out_delete_net:
@@ -556,7 +531,7 @@ out_delete_net:
 		lxc_delete_network(&handler->conf->network);
 out_abort:
 	lxc_abort(name, handler);
-	close(handler->sv[1]);
+	lxc_sync_fini(handler);
 	return -1;
 }
 

src/lxc/sync.c

+/*
+ * lxc: linux Container library
+ *
+ * (C) Copyright IBM Corp. 2007, 2008
+ *
+ * Authors:
+ * Daniel Lezcano <dlezcano at fr.ibm.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+
+#include "log.h"
+#include "start.h"
+
+lxc_log_define(lxc_sync, lxc);
+
+static int __sync_wait(int fd, int sequence)
+{
+	int sync = -1;
+	int ret;
+
+	ret = read(fd, &sync, sizeof(sync));
+	if (ret < 0) {
+		ERROR("sync wait failure : %m");
+		return -1;
+	}
+
+	if (!ret)
+		return 0;
+
+	if (sync != sequence) {
+		ERROR("invalid sequence number %d. expected %d",
+		      sync, sequence);
+		return -1;
+	}
+	return 0;
+}
+
+static int __sync_wake(int fd, int sequence)
+{
+	int sync = sequence;
+
+	if (write(fd, &sync, sizeof(sync)) < 0) {
+		ERROR("sync wake failure : %m");
+		return -1;
+	}
+	return 0;
+}
+
+static int __sync_barrier(int fd, int sequence)
+{
+	if (__sync_wake(fd, sequence))
+		return -1;
+	return __sync_wait(fd, sequence+1);
+}
+
+int lxc_sync_barrier_parent(struct lxc_handler *handler, int sequence)
+{
+	return __sync_barrier(handler->sv[0], sequence);
+}
+
+int lxc_sync_barrier_child(struct lxc_handler *handler, int sequence)
+{
+	return __sync_barrier(handler->sv[1], sequence);
+}
+
+int lxc_sync_wake_parent(struct lxc_handler *handler, int sequence)
+{
+	return __sync_wake(handler->sv[0], sequence);
+}
+
+int lxc_sync_wait_child(struct lxc_handler *handler, int sequence)
+{
+	return __sync_wait(handler->sv[1], sequence);
+}
+
+int lxc_sync_wake_child(struct lxc_handler *handler, int sequence)
+{
+	return __sync_wake(handler->sv[1], sequence);
+}
+
+int lxc_sync_init(struct lxc_handler *handler)
+{
+	if (socketpair(AF_LOCAL, SOCK_STREAM, 0, handler->sv)) {
+		SYSERROR("failed to create synchronization socketpair");
+		return -1;
+	}
+
+	/* Be sure we don't inherit this after the exec */
+	fcntl(handler->sv[0], F_SETFD, FD_CLOEXEC);
+
+	return 0;
+}
+
+void lxc_sync_fini_child(struct lxc_handler *handler)
+{
+	if (handler->sv[0] != -1) {
+		close(handler->sv[0]);
+		handler->sv[0] = -1;
+	}
+}
+
+void lxc_sync_fini_parent(struct lxc_handler *handler)
+{
+	if (handler->sv[1] != -1) {
+		close(handler->sv[1]);
+		handler->sv[1] = -1;
+	}
+}
+
+void lxc_sync_fini(struct lxc_handler *handler)
+{
+	lxc_sync_fini_child(handler);
+	lxc_sync_fini_parent(handler);
+}

src/lxc/sync.h

+/*
+ * lxc: linux Container library
+ *
+ * (C) Copyright IBM Corp. 2007, 2008
+ *
+ * Authors:
+ * Daniel Lezcano <dlezcano at fr.ibm.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+#ifndef __lxc_sync_h
+#define __lxc_sync_h
+
+struct lxc_handler;
+
+enum {
+	LXC_SYNC_CONFIGURE,
+	LXC_SYNC_POST_CONFIGURE,
+	LXC_SYNC_RESTART,
+	LXC_SYNC_POST_RESTART,
+};
+
+int lxc_sync_init(struct lxc_handler *handler);
+void lxc_sync_fini(struct lxc_handler *);
+void lxc_sync_fini_parent(struct lxc_handler *);
+void lxc_sync_fini_child(struct lxc_handler *);
+int lxc_sync_wake_child(struct lxc_handler *, int);
+int lxc_sync_wait_child(struct lxc_handler *, int);
+int lxc_sync_wake_parent(struct lxc_handler *, int);
+int lxc_sync_barrier_parent(struct lxc_handler *, int);
+int lxc_sync_barrier_child(struct lxc_handler *, int);
+
+#endif