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

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Message-Id: <20090602.002553.143476036.davem@davemloft.net>
Date:	Tue, 02 Jun 2009 00:25:53 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	patrick.ohly@...el.com
Cc:	rusty@...tcorp.com.au, 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: 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 :-/

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