netdev - Re: [PATCHv2 1/2] net: Enable 64-bit net device statistics on 32-bit architectures

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Message-ID: <1275996928.14011.83.camel@localhost>
Date:	Tue, 08 Jun 2010 12:35:28 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Miller <davem@...emloft.net>
Cc:	shemminger@...tta.com, arnd@...db.de, netdev@...r.kernel.org,
	linux-net-drivers@...arflare.com
Subject: Re: [PATCHv2 1/2] net: Enable 64-bit net device statistics on
 32-bit architectures

On Mon, 2010-06-07 at 21:18 -0700, David Miller wrote:
> From: Ben Hutchings <bhutchings@...arflare.com>
> Date: Fri, 04 Jun 2010 23:04:53 +0100
> 
> > +#if BITS_PER_LONG == 64
> > +#define NET_DEVICE_STATS_DEFINE(name)	u64 name
> > +#elif defined(__LITTLE_ENDIAN)
> > +#define NET_DEVICE_STATS_DEFINE(name)	u32 name, pad_ ## name
> > +#else
> > +#define NET_DEVICE_STATS_DEFINE(name)	u32 pad_ ## name, name
> > +#endif
> > +
>  ...
> > +	NET_DEVICE_STATS_DEFINE(rx_packets);
> > +	NET_DEVICE_STATS_DEFINE(tx_packets);
> > +	NET_DEVICE_STATS_DEFINE(rx_bytes);
>  ...
> >  	static const char fmt[] = "%30s %12lu\n";
> > +	static const char fmt64[] = "%30s %12llu\n";
>  ...
> > +	seq_printf(seq, fmt64, "total frames received", stats->rx_packets);
> > +	seq_printf(seq, fmt64, "total bytes received", stats->rx_bytes);
> > +	seq_printf(seq, fmt64, "Broadcast/Multicast Rcvd", stats->multicast);
> 
> I guess you only built this on a 64-bit platform that defines u64 as a
> long long type.

There was some disussion of formatting u64 / unsigned long long in the
past and I thought the outcome of that was that u64 should always be
defined as unsigned long long.  (See commits fe33332 and 9018113.)

[...]
> And the whole tree needs to be inspected to make sure there isn't going
> to be fallout in areas your patch didn't take care of wrt. printf format
> strings and the like.
> 
> What was always "unsigned long" is now a variable type, therefore using
> a fixed printf format string is impossible unless you always cast these
> things when passed in as printf arguments.

Yes, that's true if there are drivers out there printing members of
net_device_stats.  I admit I haven't checked for that.  (Hmm, might be
time to try Coccinelle.)

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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