[INET]: Introduce tunnel4/tunnel6

Basically this patch moves the generic tunnel protocol stuff out of
xfrm4_tunnel/xfrm6_tunnel and moves it into the new files of tunnel4.c
and tunnel6 respectively.

The reason for this is that the problem that Hugo uncovered is only
the tip of the iceberg.  The real problem is that when we removed the
dependency of ipip on xfrm4_tunnel we didn't really consider the module
case at all.

For instance, as it is it's possible to build both ipip and xfrm4_tunnel
as modules and if the latter is loaded then ipip simply won't load.

After considering the alternatives I've decided that the best way out of
this is to restore the dependency of ipip on the non-xfrm-specific part
of xfrm4_tunnel.  This is acceptable IMHO because the intention of the
removal was really to be able to use ipip without the xfrm subsystem.
This is still preserved by this patch.

So now both ipip/xfrm4_tunnel depend on the new tunnel4.c which handles
the arbitration between the two.  The order of processing is determined
by a simple integer which ensures that ipip gets processed before
xfrm4_tunnel.

The situation for ICMP handling is a little bit more complicated since
we may not have enough information to determine who it's for.  It's not
a big deal at the moment since the xfrm ICMP handlers are basically
no-ops.  In future we can deal with this when we look at ICMP caching
in general.

The user-visible change to this is the removal of the TUNNEL Kconfig
prompts.  This makes sense because it can only be used through IPCOMP
as it stands.

The addition of the new modules shouldn't introduce any problems since
module dependency will cause them to be loaded.

Oh and I also turned some unnecessary pskb's in IPv6 related to this
patch to skb's.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 113 insertions, 0 deletions

diff --git a/net/ipv4/tunnel4.c b/net/ipv4/tunnel4.c
new file mode 100644
index 000000000000..0d7d386dac22
--- /dev/null
+++ b/net/ipv4/tunnel4.c
@@ -0,0 +1,113 @@
+/* tunnel4.c: Generic IP tunnel transformer.
+ *
+ * Copyright (C) 2003 David S. Miller (davem@redhat.com)
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <net/protocol.h>
+#include <net/xfrm.h>
+
+static struct xfrm_tunnel *tunnel4_handlers;
+static DEFINE_MUTEX(tunnel4_mutex);
+
+int xfrm4_tunnel_register(struct xfrm_tunnel *handler)
+{
+        struct xfrm_tunnel **pprev;
+        int ret = -EEXIST;
+        int priority = handler->priority;
+
+        mutex_lock(&tunnel4_mutex);
+
+        for (pprev = &tunnel4_handlers; *pprev; pprev = &(*pprev)->next) {
+                if ((*pprev)->priority > priority)
+                        break;
+                if ((*pprev)->priority == priority)
+                        goto err;
+        }
+
+        handler->next = *pprev;
+        *pprev = handler;
+
+        ret = 0;
+
+err:
+        mutex_unlock(&tunnel4_mutex);
+
+        return ret;
+}
+
+EXPORT_SYMBOL(xfrm4_tunnel_register);
+
+int xfrm4_tunnel_deregister(struct xfrm_tunnel *handler)
+{
+        struct xfrm_tunnel **pprev;
+        int ret = -ENOENT;
+
+        mutex_lock(&tunnel4_mutex);
+
+        for (pprev = &tunnel4_handlers; *pprev; pprev = &(*pprev)->next) {
+                if (*pprev == handler) {
+                        *pprev = handler->next;
+                        ret = 0;
+                        break;
+                }
+        }
+
+        mutex_unlock(&tunnel4_mutex);
+
+        synchronize_net();
+
+        return ret;
+}
+
+EXPORT_SYMBOL(xfrm4_tunnel_deregister);
+
+static int tunnel4_rcv(struct sk_buff *skb)
+{
+        struct xfrm_tunnel *handler;
+
+        for (handler = tunnel4_handlers; handler; handler = handler->next)
+                if (!handler->handler(skb))
+                        return 0;
+
+        kfree_skb(skb);
+        return 0;
+}
+
+static void tunnel4_err(struct sk_buff *skb, u32 info)
+{
+        struct xfrm_tunnel *handler;
+
+        for (handler = tunnel4_handlers; handler; handler = handler->next)
+                if (!handler->err_handler(skb, info))
+                        break;
+}
+
+static struct net_protocol tunnel4_protocol = {
+        .handler        =       tunnel4_rcv,
+        .err_handler    =       tunnel4_err,
+        .no_policy      =       1,
+};
+
+static int __init tunnel4_init(void)
+{
+        if (inet_add_protocol(&tunnel4_protocol, IPPROTO_IPIP)) {
+                printk(KERN_ERR "tunnel4 init: can't add protocol\n");
+                return -EAGAIN;
+        }
+        return 0;
+}
+
+static void __exit tunnel4_fini(void)
+{
+        if (inet_del_protocol(&tunnel4_protocol, IPPROTO_IPIP))
+                printk(KERN_ERR "tunnel4 close: can't remove protocol\n");
+}
+
+module_init(tunnel4_init);
+module_exit(tunnel4_fini);
+MODULE_LICENSE("GPL");