netdev - Re: 64-bit net_device

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Message-Id: <1275576667.2106.11.camel@achroite.uk.solarflarecom.com>
Date:	Thu, 03 Jun 2010 15:51:07 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	David Miller <davem@...emloft.net>, junchangwang@...il.com,
	romieu@...zoreil.com, netdev@...r.kernel.org
Subject: Re: 64-bit net_device_stats

On Thu, 2010-06-03 at 01:38 +0200, Arnd Bergmann wrote:
> On Wednesday 02 June 2010 23:59:12 Stephen Hemminger wrote:
> > On Wed, 02 Jun 2010 22:34:29 +0100
> > Ben Hutchings <bhutchings@...arflare.com> wrote:
> > 
> > > Changing the counter types to u64 for 32-bit architectures would remove
> > > atomicity and expose half-updated counters to userland.  Changing the
> > > driver interface significantly so that atomicity is not needed would
> > > require changes to hundreds of drivers.
> > 
> > Another big issue is maintaining ABI compatibility for /proc and ioctl
> > interfaces. So bigger values would only be available through netlink,
> > and most applications using counters don't use netlink. 
> 
> Doesn't the /proc interface already allow 64 bit values in case of
> 64 bit hosts running the same 32 bit user space?

Yes.  And the most widely used consumer of /proc/net/dev, ifconfig,
already parses them as 64-bit values.

> For the ioctl interfaces, we can of course introduce additional
> ioctl commands that always deal with 64 bit values, many other
> subsystems have been extended in similar ways.
[...]

Are there any ioctl interfaces to net_device_stats?  I didn't spot any.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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