Re: crash with bridge and inconsistent handling of NETDEV_TX_OK

[David Miller <davem@davemloft.net>]

From: David Miller <davem@davemloft.net>
Date: Tue, 20 Apr 2010 16:45:05 -0700 (PDT)

> From: Mikulas Patocka <mpatocka@redhat.com>
> Date: Tue, 20 Apr 2010 19:40:56 -0400 (EDT)
> 
>> Reviewing the code further, I found one very weird commit
>> 572a9d7b6fc7f20f573664063324c086be310c42 committed to 2.6.33. What
>> it does, it changes the semantics of ndo_hard_start_xmit(). Prior to
>> the patch, the meaning was --- return zero (NETDEV_TX_OK) --- the
>> skb is consumed by the driver. Returns non-zero --- the skb is left
>> owned by the caller.  The patch changes it to return other flags in
>> bits 4-7 and changes the consumed/returned logic.
>> 
>> The problem is that there is still plenty of code that compares it
>> against NETDEV_TX_OK to find out if the skb was consumed.
> 
> Drivers are not supposed to return those new flag bits, the new flag
> bits as return values exist only in the packet scheduler path.

And BTW, NETDEV_TX_OK is only ever returned by itself, the
flag bits only get set when a non-NETDEV_TX_OK value is returned.

So we really haven't changed semantics at all, NETDEV_TX_OK (which is
zero) and non-zero are the two valid return value cases.