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

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Message-Id: <200906022338.30618.rusty@rustcorp.com.au>
Date:	Tue, 2 Jun 2009 23:38:29 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	David Miller <davem@...emloft.net>
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

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?

Thanks,
Rusty.
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