[PATCH] (1/2) fix sppp device pointer

[Stephen Hemminger <shemminger@xxxxxxxx>]

My bad, a change I put in while debugging the sealevel driver broke
all the other sync drivers.  The SPPP drivers expect that
netdev->priv points to device local structure whose first element
is a pointer to the ppp device. 

The bug was in sppp_of change that got rid of one level of indirection.

To prevent future stupidity, do some reverse lookup check in
sppp_attach and sppp_of.

diff -Nru a/drivers/net/wan/syncppp.c b/drivers/net/wan/syncppp.c
--- a/drivers/net/wan/syncppp.c Fri Oct  3 11:28:23 2003
+++ b/drivers/net/wan/syncppp.c Fri Oct  3 11:28:23 2003
@@ -1069,6 +1069,9 @@
        struct sppp *sp = &pd->sppp;
        unsigned long flags;
 
+       /* Make sure embedding is safe for sppp_of */
+       BUG_ON(sppp_of(dev) != sp);
+
        spin_lock_irqsave(&spppq_lock, flags);
        /* Initialize keepalive handler. */
        if (! spppq)
diff -Nru a/include/net/syncppp.h b/include/net/syncppp.h
--- a/include/net/syncppp.h     Fri Oct  3 11:28:23 2003
+++ b/include/net/syncppp.h     Fri Oct  3 11:28:23 2003
@@ -59,8 +59,9 @@
 
 static inline struct sppp *sppp_of(struct net_device *dev) 
 {
-       struct ppp_device *ppp = dev->priv;
-       return &ppp->sppp;
+       struct ppp_device **ppp = dev->priv;
+       BUG_ON((*ppp)->dev != dev);
+       return &(*ppp)->sppp;
 }
 
 #define PP_KEEPALIVE    0x01    /* use keepalive protocol */