[NETPOLL]: allow multiple netpoll_clients to register against one interface

This patch provides support for registering multiple netpoll clients to the
same network device.  Only one of these clients may register an rx_hook,
however.  In practice, this restriction has not been problematic.  It is
worth mentioning, though, that the current design can be easily extended to
allow for the registration of multiple rx_hooks.

The basic idea of the patch is that the rx_np pointer in the netpoll_info
structure points to the struct netpoll that has rx_hook filled in.  Aside
from this one case, there is no need for a pointer from the struct
net_device to an individual struct netpoll.

A lock is introduced to protect the setting and clearing of the np_rx
pointer.  The pointer will only be cleared upon netpoll client module
removal, and the lock should be uncontested.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 3 deletions

diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index 388cd91bc7a6..bcd0ac33f592 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -27,7 +27,8 @@ struct netpoll_info {
         spinlock_t poll_lock;
         int poll_owner;
         int rx_flags;
-        struct netpoll *np;
+        spinlock_t rx_lock;
+        struct netpoll *rx_np; /* netpoll that registered an rx_hook */
 };
 
 void netpoll_poll(struct netpoll *np);
@@ -44,11 +45,19 @@ void netpoll_queue(struct sk_buff *skb);
 static inline int netpoll_rx(struct sk_buff *skb)
 {
         struct netpoll_info *npinfo = skb->dev->npinfo;
+        unsigned long flags;
+        int ret = 0;
 
-        if (!npinfo || !npinfo->rx_flags)
+        if (!npinfo || (!npinfo->rx_np && !npinfo->rx_flags))
                 return 0;
 
-        return npinfo->np && __netpoll_rx(skb);
+        spin_lock_irqsave(&npinfo->rx_lock, flags);
+        /* check rx_flags again with the lock held */
+        if (npinfo->rx_flags && __netpoll_rx(skb))
+                ret = 1;
+        spin_unlock_irqrestore(&npinfo->rx_lock, flags);
+
+        return ret;
 }
 
 static inline void netpoll_poll_lock(struct net_device *dev)