net: move and export get_net_ns_by_pid

The function get_net_ns_by_pid(), to get a network
namespace from a pid_t, will be required in cfg80211
as well. Therefore, let's move it to net_namespace.c
and export it. We can't make it a static inline in
the !NETNS case because it needs to verify that the
given pid even exists (and return -ESRCH).
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/net_namespace.h

@@ -108,6 +108,8 @@ static inline struct net *copy_net_ns(unsigned long flags, struct net *net_ns)
 
 extern struct list_head net_namespace_list;
 
+extern struct net *get_net_ns_by_pid(pid_t pid);
+
 #ifdef CONFIG_NET_NS
 extern void __put_net(struct net *net);
 

net/core/net_namespace.c

@@ -7,6 +7,7 @@
 #include <linux/sched.h>
 #include <linux/idr.h>
 #include <linux/rculist.h>
+#include <linux/nsproxy.h>
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 
@@ -201,6 +202,26 @@ struct net *copy_net_ns(unsigned long flags, struct net *old_net)
 }
 #endif
 
+struct net *get_net_ns_by_pid(pid_t pid)
+{
+	struct task_struct *tsk;
+	struct net *net;
+
+	/* Lookup the network namespace */
+	net = ERR_PTR(-ESRCH);
+	rcu_read_lock();
+	tsk = find_task_by_vpid(pid);
+	if (tsk) {
+		struct nsproxy *nsproxy;
+		nsproxy = task_nsproxy(tsk);
+		if (nsproxy)
+			net = get_net(nsproxy->net_ns);
+	}
+	rcu_read_unlock();
+	return net;
+}
+EXPORT_SYMBOL_GPL(get_net_ns_by_pid);
+
 static int __init net_ns_init(void)
 {
 	struct net_generic *ng;

net/core/rtnetlink.c

@@ -35,7 +35,6 @@
 #include <linux/security.h>
 #include <linux/mutex.h>
 #include <linux/if_addr.h>
-#include <linux/nsproxy.h>
 
 #include <asm/uaccess.h>
 #include <asm/system.h>
@@ -52,6 +51,7 @@
 #include <net/pkt_sched.h>
 #include <net/fib_rules.h>
 #include <net/rtnetlink.h>
+#include <net/net_namespace.h>
 
 struct rtnl_link
 {
@@ -725,25 +725,6 @@ static const struct nla_policy ifla_info_policy[IFLA_INFO_MAX+1] = {
 	[IFLA_INFO_DATA]	= { .type = NLA_NESTED },
 };
 
-static struct net *get_net_ns_by_pid(pid_t pid)
-{
-	struct task_struct *tsk;
-	struct net *net;
-
-	/* Lookup the network namespace */
-	net = ERR_PTR(-ESRCH);
-	rcu_read_lock();
-	tsk = find_task_by_vpid(pid);
-	if (tsk) {
-		struct nsproxy *nsproxy;
-		nsproxy = task_nsproxy(tsk);
-		if (nsproxy)
-			net = get_net(nsproxy->net_ns);
-	}
-	rcu_read_unlock();
-	return net;
-}
-
 static int validate_linkmsg(struct net_device *dev, struct nlattr *tb[])
 {
 	if (dev) {