[PATCH 1/4] net: skb_orphan on dev_hard_start_xmit

[David Miller]

From: Rusty Russell <rusty at rustcorp.com.au>
Date: Tue, 2 Jun 2009 23:38:29 +0930

> On Tue, 2 Jun 2009 04:55:53 pm David Miller wrote:
>> From: Patrick Ohly <patrick.ohly at intel.com>
>> Date: Mon, 01 Jun 2009 21:47:22 +0200
>>
>> > On Fri, 2009-05-29 at 23:44 +0930, Rusty Russell wrote:
>> >> This patch adds skb_orphan to the start of dev_hard_start_xmit(): it
>> >> can be premature in the NETDEV_TX_BUSY case, but that's uncommon.
>> >
>> > Would it be possible to make the new skb_orphan() at the start of
>> > dev_hard_start_xmit() conditionally so that it is not executed for
>> > packets that are to be time stamped?
>> >
>> > As discussed before
>> > (http://article.gmane.org/gmane.linux.network/121378/), the skb->sk
>> > socket pointer is required for sending back the send time stamp from
>> > inside the device driver. Calling skb_orphan() unconditionally as in
>> > this patch would break the hardware time stamping of outgoing packets.
>>
>> Indeed, we need to check that case, at a minimum.
>>
>> And there are other potentially other problems.  For example, I
>> wonder how this interacts with the new TX MMAP af_packet support
>> in net-next-2.6 :-/
> 
> I think I'll do this in the driver for now, and let's revisit doing it 
> generically later?

That might be the best course of action for the time being.
This whole area is a rat's nest.