[RTNL]: Message handler registration interface

This patch adds a new interface to register rtnetlink message
handlers replacing the exported rtnl_links[] array which
required many message handlers to be exported unnecessarly.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 166 insertions, 22 deletions

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 33ea8eac7fe..fb1630d82dd 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -50,12 +50,18 @@
 #include <net/sock.h>
 #include <net/pkt_sched.h>
 #include <net/fib_rules.h>
-#include <net/netlink.h>
+#include <net/rtnetlink.h>
 #ifdef CONFIG_NET_WIRELESS_RTNETLINK
 #include <linux/wireless.h>
 #include <net/iw_handler.h>
 #endif  /* CONFIG_NET_WIRELESS_RTNETLINK */
 
+struct rtnl_link
+{
+        rtnl_doit_func          doit;
+        rtnl_dumpit_func        dumpit;
+};
+
 static DEFINE_MUTEX(rtnl_mutex);
 static struct sock *rtnl;
 
@@ -95,7 +101,151 @@ int rtattr_parse(struct rtattr *tb[], int maxattr, struct rtattr *rta, int len)
         return 0;
 }
 
-struct rtnetlink_link * rtnetlink_links[NPROTO];
+struct rtnl_link *rtnl_msg_handlers[NPROTO];
+
+static inline int rtm_msgindex(int msgtype)
+{
+        int msgindex = msgtype - RTM_BASE;
+
+        /*
+         * msgindex < 0 implies someone tried to register a netlink
+         * control code. msgindex >= RTM_NR_MSGTYPES may indicate that
+         * the message type has not been added to linux/rtnetlink.h
+         */
+        BUG_ON(msgindex < 0 || msgindex >= RTM_NR_MSGTYPES);
+
+        return msgindex;
+}
+
+static rtnl_doit_func rtnl_get_doit(int protocol, int msgindex)
+{
+        struct rtnl_link *tab;
+
+        tab = rtnl_msg_handlers[protocol];
+        if (tab == NULL || tab->doit == NULL)
+                tab = rtnl_msg_handlers[PF_UNSPEC];
+
+        return tab ? tab->doit : NULL;
+}
+
+static rtnl_dumpit_func rtnl_get_dumpit(int protocol, int msgindex)
+{
+        struct rtnl_link *tab;
+
+        tab = rtnl_msg_handlers[protocol];
+        if (tab == NULL || tab->dumpit == NULL)
+                tab = rtnl_msg_handlers[PF_UNSPEC];
+
+        return tab ? tab->dumpit : NULL;
+}
+
+/**
+ * __rtnl_register - Register a rtnetlink message type
+ * @protocol: Protocol family or PF_UNSPEC
+ * @msgtype: rtnetlink message type
+ * @doit: Function pointer called for each request message
+ * @dumpit: Function pointer called for each dump request (NLM_F_DUMP) message
+ *
+ * Registers the specified function pointers (at least one of them has
+ * to be non-NULL) to be called whenever a request message for the
+ * specified protocol family and message type is received.
+ *
+ * The special protocol family PF_UNSPEC may be used to define fallback
+ * function pointers for the case when no entry for the specific protocol
+ * family exists.
+ *
+ * Returns 0 on success or a negative error code.
+ */
+int __rtnl_register(int protocol, int msgtype,
+                    rtnl_doit_func doit, rtnl_dumpit_func dumpit)
+{
+        struct rtnl_link *tab;
+        int msgindex;
+
+        BUG_ON(protocol < 0 || protocol >= NPROTO);
+        msgindex = rtm_msgindex(msgtype);
+
+        tab = rtnl_msg_handlers[protocol];
+        if (tab == NULL) {
+                tab = kcalloc(RTM_NR_MSGTYPES, sizeof(*tab), GFP_KERNEL);
+                if (tab == NULL)
+                        return -ENOBUFS;
+
+                rtnl_msg_handlers[protocol] = tab;
+        }
+
+        if (doit)
+                tab[msgindex].doit = doit;
+
+        if (dumpit)
+                tab[msgindex].dumpit = dumpit;
+
+        return 0;
+}
+
+EXPORT_SYMBOL_GPL(__rtnl_register);
+
+/**
+ * rtnl_register - Register a rtnetlink message type
+ *
+ * Identical to __rtnl_register() but panics on failure. This is useful
+ * as failure of this function is very unlikely, it can only happen due
+ * to lack of memory when allocating the chain to store all message
+ * handlers for a protocol. Meant for use in init functions where lack
+ * of memory implies no sense in continueing.
+ */
+void rtnl_register(int protocol, int msgtype,
+                   rtnl_doit_func doit, rtnl_dumpit_func dumpit)
+{
+        if (__rtnl_register(protocol, msgtype, doit, dumpit) < 0)
+                panic("Unable to register rtnetlink message handler, "
+                      "protocol = %d, message type = %d\n",
+                      protocol, msgtype);
+}
+
+EXPORT_SYMBOL_GPL(rtnl_register);
+
+/**
+ * rtnl_unregister - Unregister a rtnetlink message type
+ * @protocol: Protocol family or PF_UNSPEC
+ * @msgtype: rtnetlink message type
+ *
+ * Returns 0 on success or a negative error code.
+ */
+int rtnl_unregister(int protocol, int msgtype)
+{
+        int msgindex;
+
+        BUG_ON(protocol < 0 || protocol >= NPROTO);
+        msgindex = rtm_msgindex(msgtype);
+
+        if (rtnl_msg_handlers[protocol] == NULL)
+                return -ENOENT;
+
+        rtnl_msg_handlers[protocol][msgindex].doit = NULL;
+        rtnl_msg_handlers[protocol][msgindex].dumpit = NULL;
+
+        return 0;
+}
+
+EXPORT_SYMBOL_GPL(rtnl_unregister);
+
+/**
+ * rtnl_unregister_all - Unregister all rtnetlink message type of a protocol
+ * @protocol : Protocol family or PF_UNSPEC
+ *
+ * Identical to calling rtnl_unregster() for all registered message types
+ * of a certain protocol family.
+ */
+void rtnl_unregister_all(int protocol)
+{
+        BUG_ON(protocol < 0 || protocol >= NPROTO);
+
+        kfree(rtnl_msg_handlers[protocol]);
+        rtnl_msg_handlers[protocol] = NULL;
+}
+
+EXPORT_SYMBOL_GPL(rtnl_unregister_all);
 
 static const int rtm_min[RTM_NR_FAMILIES] =
 {
@@ -648,7 +798,7 @@ errout:
         return err;
 }
 
-static int rtnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb)
+int rtnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb)
 {
         int idx;
         int s_idx = cb->family;
@@ -659,12 +809,12 @@ static int rtnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb)
                 int type = cb->nlh->nlmsg_type-RTM_BASE;
                 if (idx < s_idx || idx == PF_PACKET)
                         continue;
-                if (rtnetlink_links[idx] == NULL ||
-                    rtnetlink_links[idx][type].dumpit == NULL)
+                if (rtnl_msg_handlers[idx] == NULL ||
+                    rtnl_msg_handlers[idx][type].dumpit == NULL)
                         continue;
                 if (idx > s_idx)
                         memset(&cb->args[0], 0, sizeof(cb->args));
-                if (rtnetlink_links[idx][type].dumpit(skb, cb))
+                if (rtnl_msg_handlers[idx][type].dumpit(skb, cb))
                         break;
         }
         cb->family = idx;
@@ -672,6 +822,8 @@ static int rtnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb)
         return skb->len;
 }
 
+EXPORT_SYMBOL_GPL(rtnl_dump_all);
+
 void rtmsg_ifinfo(int type, struct net_device *dev, unsigned change)
 {
         struct sk_buff *skb;
@@ -703,8 +855,7 @@ static int rtattr_max;
 static __inline__ int
 rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh, int *errp)
 {
-        struct rtnetlink_link *link;
-        struct rtnetlink_link *link_tab;
+        rtnl_doit_func doit;
         int sz_idx, kind;
         int min_len;
         int family;
@@ -737,11 +888,6 @@ rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh, int *errp)
                 return -1;
         }
 
-        link_tab = rtnetlink_links[family];
-        if (link_tab == NULL)
-                link_tab = rtnetlink_links[PF_UNSPEC];
-        link = &link_tab[type];
-
         sz_idx = type>>2;
         kind = type&3;
 
@@ -751,14 +897,14 @@ rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh, int *errp)
         }
 
         if (kind == 2 && nlh->nlmsg_flags&NLM_F_DUMP) {
-                if (link->dumpit == NULL)
-                        link = &(rtnetlink_links[PF_UNSPEC][type]);
+                rtnl_dumpit_func dumpit;
 
-                if (link->dumpit == NULL)
+                dumpit = rtnl_get_dumpit(family, type);
+                if (dumpit == NULL)
                         goto err_inval;
 
                 if ((*errp = netlink_dump_start(rtnl, skb, nlh,
-                                                link->dumpit, NULL)) != 0) {
+                                                dumpit, NULL)) != 0) {
                         return -1;
                 }
 
@@ -787,11 +933,10 @@ rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh, int *errp)
                 }
         }
 
-        if (link->doit == NULL)
-                link = &(rtnetlink_links[PF_UNSPEC][type]);
-        if (link->doit == NULL)
+        doit = rtnl_get_doit(family, type);
+        if (doit == NULL)
                 goto err_inval;
-        err = link->doit(skb, nlh, (void *)&rta_buf[0]);
+        err = doit(skb, nlh, (void *)&rta_buf[0]);
 
         *errp = err;
         return err;
@@ -886,7 +1031,6 @@ void __init rtnetlink_init(void)
 EXPORT_SYMBOL(__rta_fill);
 EXPORT_SYMBOL(rtattr_strlcpy);
 EXPORT_SYMBOL(rtattr_parse);
-EXPORT_SYMBOL(rtnetlink_links);
 EXPORT_SYMBOL(rtnetlink_put_metrics);
 EXPORT_SYMBOL(rtnl_lock);
 EXPORT_SYMBOL(rtnl_trylock);