Subject: Re: [RFC PATCH v2] Gemini: Gigabit ethernet driver

From: Stephen Hemminger <[email-masked]>
Date: Wed, 29 Dec 2010 11:28:27 -0800

On Wed, 29 Dec 2010 19:30:41 +0100
Eric Dumazet <[email-masked]> wrote:

> Le mercredi 29 décembre 2010 à 17:56 +0100, Hans Ulli Kroll a écrit :
> > 
> > On Mon, 27 Dec 2010, Stephen Hemminger wrote:
> > 
> > > 
> > > 
> > > ----- Original Message -----
> > > > On Mon, 2010-12-27 at 20:21 +0100, Hans Ulli Kroll wrote:
> > > > [...]
> > > > > BTW:
> > > > >
> > > > > Why u64_stats ?
> > > > > I see only a few driver are using u64_stats.
> > > > > vlan, br_device and some intel driver
> > > > > no gigabit driver for marvell devices uses u64_stats
> > > > 
> > > > All new net drivers should implement 64-bit stats. net_device_stats is
> > > > kept for backward compatibility because we couldn't change all the
> > > > existing drivers at once (it's not a simple change for all of them).
> > > > 
> > > > Ben.
> > > 
> > > BS. drivers with old stats are fine. 64 bit only really matters
> > > at higher speed. Anyway, it is the kind of thing that can easily
> > > be fixed later after driver is merged.
> > > 
> > > 
> > 
> > I've readed the Intel driver.
> > 
> > So we must also implement to old net_stats interface, for backward 
> > compatibility ?
> 
> If you implement new (64bit) stats, old one is not used at all.
> 
> Check net/core/dev.c : dev_get_stats()
> 
> If ndo_get_stats64() method is implemented, its called, and legacy
> interfaces are ignored.

It looks like the comment/documentation in netdevice.h is incorrect.

 * struct net_device_stats* (*ndo_get_stats)(struct net_device *dev);
 *	Called when a user wants to get the network device usage
 *	statistics. Drivers must do one of the following:
 *	1. Define @ndo_get_stats64 to fill in a zero-initialised
 *	   rtnl_link_stats64 structure passed by the caller.
 *	2. Define @ndo_get_stats to update a net_device_stats structure
 *	   (which should normally be dev->stats) and return a pointer to
 *	   it. The structure may be changed asynchronously only if each
 *	   field is written atomically.
 *	3. Update dev->stats asynchronously and atomically, and define
 *	   neither operation.

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