net: Introduce possible_net_t

Having to say
> #ifdef CONFIG_NET_NS
> 	struct net *net;
> #endif

in structures is a little bit wordy and a little bit error prone.

Instead it is possible to say:
> typedef struct {
> #ifdef CONFIG_NET_NS
>       struct net *net;
> #endif
> } possible_net_t;

And then in a header say:

> 	possible_net_t net;

Which is cleaner and easier to use and easier to test, as the
possible_net_t is always there no matter what the compile options.

Further this allows read_pnet and write_pnet to be functions in all
cases which is better at catching typos.

This change adds possible_net_t, updates the definitions of read_pnet
and write_pnet, updates optional struct net * variables that
write_pnet uses on to have the type possible_net_t, and finally fixes
up the b0rked users of read_pnet and write_pnet.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1721,9 +1721,7 @@ struct net_device {
 	struct netpoll_info __rcu	*npinfo;
 #endif
 
-#ifdef CONFIG_NET_NS
-	struct net		*nd_net;
-#endif
+	possible_net_t			nd_net;
 
 	/* mid-layer private */
 	union {
@@ -1863,9 +1861,7 @@ struct net *dev_net(const struct net_device *dev)
 static inline
 void dev_net_set(struct net_device *dev, struct net *net)
 {
-#ifdef CONFIG_NET_NS
-	dev->nd_net = net;
-#endif
+	write_pnet(&dev->nd_net, net);
 }
 
 static inline bool netdev_uses_dsa(struct net_device *dev)

include/net/cfg80211.h

@@ -3183,10 +3183,8 @@ struct wiphy {
 	const struct ieee80211_ht_cap *ht_capa_mod_mask;
 	const struct ieee80211_vht_cap *vht_capa_mod_mask;
 
-#ifdef CONFIG_NET_NS
 	/* the network namespace this phy lives in currently */
-	struct net *_net;
-#endif
+	possible_net_t _net;
 
 #ifdef CONFIG_CFG80211_WEXT
 	const struct iw_handler_def *wext;

include/net/genetlink.h

@@ -92,9 +92,7 @@ struct genl_info {
 	struct genlmsghdr *	genlhdr;
 	void *			userhdr;
 	struct nlattr **	attrs;
-#ifdef CONFIG_NET_NS
-	struct net *		_net;
-#endif
+	possible_net_t		_net;
 	void *			user_ptr[2];
 	struct sock *		dst_sk;
 };

include/net/inet_hashtables.h

@@ -76,9 +76,7 @@ struct inet_ehash_bucket {
  * ports are created in O(1) time?  I thought so. ;-)	-DaveM
  */
 struct inet_bind_bucket {
-#ifdef CONFIG_NET_NS
-	struct net		*ib_net;
-#endif
+	possible_net_t		ib_net;
 	unsigned short		port;
 	signed char		fastreuse;
 	signed char		fastreuseport;

include/net/ip_vs.h

@@ -47,13 +47,13 @@ static inline struct net *skb_net(const struct sk_buff *skb)
 	 * Start with the most likely hit
 	 * End with BUG
 	 */
-	if (likely(skb->dev && skb->dev->nd_net))
+	if (likely(skb->dev && dev_net(skb->dev)))
 		return dev_net(skb->dev);
 	if (skb_dst(skb) && skb_dst(skb)->dev)
 		return dev_net(skb_dst(skb)->dev);
 	WARN(skb->sk, "Maybe skb_sknet should be used in %s() at line:%d\n",
 		      __func__, __LINE__);
-	if (likely(skb->sk && skb->sk->sk_net))
+	if (likely(skb->sk && sock_net(skb->sk)))
 		return sock_net(skb->sk);
 	pr_err("There is no net ptr to find in the skb in %s() line:%d\n",
 		__func__, __LINE__);
@@ -71,11 +71,11 @@ static inline struct net *skb_sknet(const struct sk_buff *skb)
 #ifdef CONFIG_NET_NS
 #ifdef CONFIG_IP_VS_DEBUG
 	/* Start with the most likely hit */
-	if (likely(skb->sk && skb->sk->sk_net))
+	if (likely(skb->sk && sock_net(skb->sk)))
 		return sock_net(skb->sk);
 	WARN(skb->dev, "Maybe skb_net should be used instead in %s() line:%d\n",
 		       __func__, __LINE__);
-	if (likely(skb->dev && skb->dev->nd_net))
+	if (likely(skb->dev && dev_net(skb->dev)))
 		return dev_net(skb->dev);
 	pr_err("There is no net ptr to find in the skb in %s() line:%d\n",
 		__func__, __LINE__);

include/net/neighbour.h

@@ -65,9 +65,7 @@ enum {
 };
 
 struct neigh_parms {
-#ifdef CONFIG_NET_NS
-	struct net *net;
-#endif
+	possible_net_t net;
 	struct net_device *dev;
 	struct list_head list;
 	int	(*neigh_setup)(struct neighbour *);
@@ -167,9 +165,7 @@ struct neigh_ops {
 
 struct pneigh_entry {
 	struct pneigh_entry	*next;
-#ifdef CONFIG_NET_NS
-	struct net		*net;
-#endif
+	possible_net_t		net;
 	struct net_device	*dev;
 	u8			flags;
 	u8			key[0];

include/net/net_namespace.h

@@ -231,24 +231,27 @@ int net_eq(const struct net *net1, const struct net *net2)
 #endif
 
 
+typedef struct {
 #ifdef CONFIG_NET_NS
-
-static inline void write_pnet(struct net **pnet, struct net *net)
-{
-	*pnet = net;
-}
-
-static inline struct net *read_pnet(struct net * const *pnet)
-{
-	return *pnet;
-}
-
-#else
-
-#define write_pnet(pnet, net)	do { (void)(net);} while (0)
-#define read_pnet(pnet)		(&init_net)
-
+	struct net *net;
 #endif
+} possible_net_t;
+
+static inline void write_pnet(possible_net_t *pnet, struct net *net)
+{
+#ifdef CONFIG_NET_NS
+	pnet->net = net;
+#endif
+}
+
+static inline struct net *read_pnet(const possible_net_t *pnet)
+{
+#ifdef CONFIG_NET_NS
+	return pnet->net;
+#else
+	return &init_net;
+#endif
+}
 
 #define for_each_net(VAR)				\
 	list_for_each_entry(VAR, &net_namespace_list, list)

include/net/netfilter/nf_conntrack.h

@@ -95,9 +95,8 @@ struct nf_conn {
 	/* Timer function; drops refcnt when it goes off. */
 	struct timer_list timeout;
 
-#ifdef CONFIG_NET_NS
-	struct net *ct_net;
-#endif
+	possible_net_t ct_net;
+
 	/* all members below initialized via memset */
 	u8 __nfct_init_offset[0];
 

include/net/sock.h

@@ -190,9 +190,7 @@ struct sock_common {
 		struct hlist_nulls_node skc_portaddr_node;
 	};
 	struct proto		*skc_prot;
-#ifdef CONFIG_NET_NS
-	struct net	 	*skc_net;
-#endif
+	possible_net_t		skc_net;
 
 #if IS_ENABLED(CONFIG_IPV6)
 	struct in6_addr		skc_v6_daddr;

include/net/xfrm.h

@@ -126,9 +126,7 @@ struct xfrm_state_walk {
 
 /* Full description of state of transformer. */
 struct xfrm_state {
-#ifdef CONFIG_NET_NS
-	struct net		*xs_net;
-#endif
+	possible_net_t		xs_net;
 	union {
 		struct hlist_node	gclist;
 		struct hlist_node	bydst;
@@ -522,9 +520,7 @@ struct xfrm_policy_queue {
 };
 
 struct xfrm_policy {
-#ifdef CONFIG_NET_NS
-	struct net		*xp_net;
-#endif
+	possible_net_t		xp_net;
 	struct hlist_node	bydst;
 	struct hlist_node	byidx;
 

net/9p/trans_fd.c

@@ -940,7 +940,7 @@ p9_fd_create_tcp(struct p9_client *client, const char *addr, char *args)
 	sin_server.sin_family = AF_INET;
 	sin_server.sin_addr.s_addr = in_aton(addr);
 	sin_server.sin_port = htons(opts.port);
-	err = __sock_create(read_pnet(&current->nsproxy->net_ns), PF_INET,
+	err = __sock_create(current->nsproxy->net_ns, PF_INET,
 			    SOCK_STREAM, IPPROTO_TCP, &csocket, 1);
 	if (err) {
 		pr_err("%s (%d): problem creating socket\n",
@@ -988,7 +988,7 @@ p9_fd_create_unix(struct p9_client *client, const char *addr, char *args)
 
 	sun_server.sun_family = PF_UNIX;
 	strcpy(sun_server.sun_path, addr);
-	err = __sock_create(read_pnet(&current->nsproxy->net_ns), PF_UNIX,
+	err = __sock_create(current->nsproxy->net_ns, PF_UNIX,
 			    SOCK_STREAM, 0, &csocket, 1);
 	if (err < 0) {
 		pr_err("%s (%d): problem creating socket\n",

net/ipv4/ipmr.c

@@ -73,9 +73,7 @@
 
 struct mr_table {
 	struct list_head	list;
-#ifdef CONFIG_NET_NS
-	struct net		*net;
-#endif
+	possible_net_t		net;
 	u32			id;
 	struct sock __rcu	*mroute_sk;
 	struct timer_list	ipmr_expire_timer;

net/ipv6/addrlabel.c

@@ -29,9 +29,7 @@
  * Policy Table
  */
 struct ip6addrlbl_entry {
-#ifdef CONFIG_NET_NS
-	struct net *lbl_net;
-#endif
+	possible_net_t lbl_net;
 	struct in6_addr prefix;
 	int prefixlen;
 	int ifindex;
@@ -237,9 +235,7 @@ static struct ip6addrlbl_entry *ip6addrlbl_alloc(struct net *net,
 	newp->addrtype = addrtype;
 	newp->label = label;
 	INIT_HLIST_NODE(&newp->list);
-#ifdef CONFIG_NET_NS
-	newp->lbl_net = net;
-#endif
+	write_pnet(&newp->lbl_net, net);
 	atomic_set(&newp->refcnt, 1);
 	return newp;
 }

net/ipv6/ip6mr.c

@@ -56,9 +56,7 @@
 
 struct mr6_table {
 	struct list_head	list;
-#ifdef CONFIG_NET_NS
-	struct net		*net;
-#endif
+	possible_net_t		net;
 	u32			id;
 	struct sock		*mroute6_sk;
 	struct timer_list	ipmr_expire_timer;

net/openvswitch/datapath.h

@@ -84,10 +84,8 @@ struct datapath {
 	/* Stats. */
 	struct dp_stats_percpu __percpu *stats_percpu;
 
-#ifdef CONFIG_NET_NS
 	/* Network namespace ref. */
-	struct net *net;
-#endif
+	possible_net_t net;
 
 	u32 user_features;
 };

net/packet/internal.h

@@ -74,9 +74,7 @@ extern struct mutex fanout_mutex;
 #define PACKET_FANOUT_MAX	256
 
 struct packet_fanout {
-#ifdef CONFIG_NET_NS
-	struct net		*net;
-#endif
+	possible_net_t		net;
 	unsigned int		num_members;
 	u16			id;
 	u8			type;