netdev - Re: [PATCH 1/4] net: skb_orphan on dev_hard_start

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Date:	Tue, 02 Jun 2009 17:14:18 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	rusty@...tcorp.com.au
Cc:	patrick.ohly@...el.com, netdev@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, divy@...lsio.com,
	rolandd@...co.com, xemul@...nvz.org, dcbw@...hat.com,
	libertas-dev@...ts.infradead.org
Subject: Re: [PATCH 1/4] net: skb_orphan on dev_hard_start_xmit

From: Rusty Russell <rusty@...tcorp.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@...el.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.
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