netlink: add a start callback for starting a netlink dump

The start callback allows the caller to set up a context for the
dump callbacks. Presumably, the context can then be destroyed in
the done callback.

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 20 insertions, 0 deletions

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 59651af8cc27..81dc1bb6e016 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2915,6 +2915,7 @@ int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
 
         cb = &nlk->cb;
         memset(cb, 0, sizeof(*cb));
+        cb->start = control->start;
         cb->dump = control->dump;
         cb->done = control->done;
         cb->nlh = nlh;
@@ -2927,6 +2928,9 @@ int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
 
         mutex_unlock(nlk->cb_mutex);
 
+        if (cb->start)
+                cb->start(cb);
+
         ret = netlink_dump(sk);
         sock_put(sk);
 
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index bc0e504f33a6..8e63662c6fb0 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -513,6 +513,20 @@ void *genlmsg_put(struct sk_buff *skb, u32 portid, u32 seq,
 }
 EXPORT_SYMBOL(genlmsg_put);
 
+static int genl_lock_start(struct netlink_callback *cb)
+{
+        /* our ops are always const - netlink API doesn't propagate that */
+        const struct genl_ops *ops = cb->data;
+        int rc = 0;
+
+        if (ops->start) {
+                genl_lock();
+                rc = ops->start(cb);
+                genl_unlock();
+        }
+        return rc;
+}
+
 static int genl_lock_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 {
         /* our ops are always const - netlink API doesn't propagate that */
@@ -577,6 +591,7 @@ static int genl_family_rcv_msg(struct genl_family *family,
                                 .module = family->module,
                                 /* we have const, but the netlink API doesn't */
                                 .data = (void *)ops,
+                                .start = genl_lock_start,
                                 .dump = genl_lock_dumpit,
                                 .done = genl_lock_done,
                         };
@@ -588,6 +603,7 @@ static int genl_family_rcv_msg(struct genl_family *family,
                 } else {
                         struct netlink_dump_control c = {
                                 .module = family->module,
+                                .start = ops->start,
                                 .dump = ops->dumpit,
                                 .done = ops->done,
                         };