netdev - Re: [PATCH 01/10] net: introduce time stamping wrapper for netif

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Message-ID: <20110610111924.54fede19@nehalam.ftrdhcpuser.net>
Date:	Fri, 10 Jun 2011 11:19:24 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Richard Cochran <richardcochran@...il.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: [PATCH 01/10] net: introduce time stamping wrapper for
 netif_rx.

On Fri, 10 Jun 2011 19:27:47 +0200
Richard Cochran <richardcochran@...il.com> wrote:

> On Fri, Jun 10, 2011 at 08:20:56AM -0700, Stephen Hemminger wrote:
> > On Fri, 10 Jun 2011 17:06:59 +0200
> > Richard Cochran <richardcochran@...il.com> wrote:
> > 
> > > +static inline int netif_rx_defer(struct sk_buff *skb)
> > > +{
> > > +	if (skb_defer_rx_timestamp(skb))
> > > +		return NET_RX_SUCCESS;
> > > +	return netif_rx(skb);
> > > +}
> > 
> > Obvious question why not just put this in netif_rx.
> 
> Well, if a packet gets defered, then that means that the PHY driver
> has decided to hold the packet until it obtains the time stamp from
> the PHY hardware. Then, the driver delivers the packet using netif_rx.
> 
> So, we need to have two methods to deliver a frame, one with and one
> without the hook, otherwise you get packets going round in circles.
> 
> Take a look at the one PHY driver using this (so far), on line 1017 of
> drivers/net/phy/dp83640.c, to see how it works.
> 
> Thanks,
> Richard
> 
> PS I did consider at renaming netif_rx to __netif_rx and then
> implementing netif_rx as shown above, but I found many, many callers
> of netif_rx which are not drivers, so I worry that bad side effects
> would appear from such a change.

Why not use a timestamp present flag like the receive hashing code
already does.
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