From 2d56d1b0560698827d40e8eb16cc20a3571081e4 Mon Sep 17 00:00:00 2001
From: Pavel Emelyanov <xemul@parallels.com>
Date: Thu, 2 Aug 2012 07:55:05 +0400
Subject: [PATCH] ns: Add ability to save original ns and restoring it back
 while switcing

This will be required for parasite transport socket creation -- it will
have to be created in a net ns we're putting parasite in and then we'll
have to restore it back to original to go on dumping.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
---
 include/namespaces.h |  3 ++-
 ipc_ns.c             |  2 +-
 namespaces.c         | 37 +++++++++++++++++++++++++++++++++----
 uts_ns.c             |  2 +-
 4 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/include/namespaces.h b/include/namespaces.h
index eed805c7a..244107ca6 100644
--- a/include/namespaces.h
+++ b/include/namespaces.h
@@ -7,5 +7,6 @@ int dump_namespaces(struct pid *pid, unsigned int ns_flags);
 int prepare_namespace(int pid, unsigned long clone_flags);
 struct cr_options;
 int try_show_namespaces(int pid, struct cr_options *);
-int switch_ns(int pid, int type, char *ns);
+int switch_ns(int pid, int type, char *ns, int *rst);
+int restore_ns(int rst, int type);
 #endif
diff --git a/ipc_ns.c b/ipc_ns.c
index f35852c99..390ac8048 100644
--- a/ipc_ns.c
+++ b/ipc_ns.c
@@ -456,7 +456,7 @@ int dump_ipc_ns(int ns_pid, const struct cr_fdset *fdset)
 {
 	int ret;
 
-	ret = switch_ns(ns_pid, CLONE_NEWIPC, "ipc");
+	ret = switch_ns(ns_pid, CLONE_NEWIPC, "ipc", NULL);
 	if (ret < 0)
 		return ret;
 
diff --git a/namespaces.c b/namespaces.c
index 9e3644193..ee6c59a10 100644
--- a/namespaces.c
+++ b/namespaces.c
@@ -9,7 +9,7 @@
 #include "mount.h"
 #include "namespaces.h"
 
-int switch_ns(int pid, int type, char *ns)
+int switch_ns(int pid, int type, char *ns, int *rst)
 {
 	char buf[32];
 	int nsfd;
@@ -19,15 +19,44 @@ int switch_ns(int pid, int type, char *ns)
 	nsfd = open(buf, O_RDONLY);
 	if (nsfd < 0) {
 		pr_perror("Can't open ipcns file");
-		goto out;
+		goto err_ns;
+	}
+
+	if (rst) {
+		snprintf(buf, sizeof(buf), "/proc/self/ns/%s", ns);
+		*rst = open(buf, O_RDONLY);
+		if (*rst < 0) {
+			pr_perror("Can't open ns file");
+			goto err_rst;
+		}
 	}
 
 	ret = setns(nsfd, type);
-	if (ret < 0)
+	if (ret < 0) {
 		pr_perror("Can't setns %d/%s", pid, ns);
+		goto err_set;
+	}
 
 	close(nsfd);
-out:
+	return 0;
+
+err_set:
+	if (rst)
+		close(*rst);
+err_rst:
+	close(nsfd);
+err_ns:
+	return -1;
+}
+
+int restore_ns(int rst, int type)
+{
+	int ret;
+
+	ret = setns(rst, type);
+	if (ret < 0)
+		pr_perror("Can't restore ns back");
+
 	return ret;
 }
 
diff --git a/uts_ns.c b/uts_ns.c
index b6541bc37..c4ddf4072 100644
--- a/uts_ns.c
+++ b/uts_ns.c
@@ -18,7 +18,7 @@ int dump_uts_ns(int ns_pid, struct cr_fdset *fdset)
 	struct utsname ubuf;
 	UtsnsEntry ue = UTSNS_ENTRY__INIT;
 
-	ret = switch_ns(ns_pid, CLONE_NEWUTS, "uts");
+	ret = switch_ns(ns_pid, CLONE_NEWUTS, "uts", NULL);
 	if (ret < 0)
 		return ret;