[PATCH 1/4] net: skb_orphan on dev_hard_start_xmit

Patrick Ohly patrick.ohly at intel.com
Mon Jun 1 15:47:22 EDT 2009

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.

This should work without much overhead (skb_tx() expands to a lookup of
the skb_shared_info):
if (!skb_tx(skb)->flags)

Instead of looking at the individual skb_shared_tx "hardware" and
"software" bits I'm just checking the whole byte here because it is
shorter and perhaps faster. Semantically the result is the same.

Best Regards, Patrick Ohly

The content of this message is my personal opinion only and although
I am an employee of Intel, the statements I make here in no way
represent Intel's position on the issue, nor am I authorized to speak
on behalf of Intel on this matter.

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