netdev - Re: [PATCH net-next] tcp: tcp_sendmsg() wrong access to sk_route

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Message-ID: <1322500843.26733.2.camel@bwh-desktop>
Date:	Mon, 28 Nov 2011 17:20:42 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Joe Perches <joe@...ches.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Michał Mirosław <mirq-linux@...e.qmqm.pl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH net-next] tcp: tcp_sendmsg() wrong access to
 sk_route_caps

On Mon, 2011-11-28 at 08:54 -0800, Joe Perches wrote:
> On Mon, 2011-11-28 at 17:04 +0100, Eric Dumazet wrote:
> > Le lundi 28 novembre 2011 à 02:46 -0800, Joe Perches a écrit :
> > > On Mon, 2011-11-28 at 11:27 +0100, Eric Dumazet wrote:
> > > > +	sg = !!(sk->sk_route_caps & NETIF_F_SG);
> > > As sg is now bool, using !! is unnecessary.
> > > A commit was done recently to remove one.
> > > 3ad9b358e03fd9dbf6705721490c811b666b0fe2
> > Hmm... I find it dangerous and error prone. Obviously not at the time we
> > commit such changes, but later, because a future reader might be fooled.
> > Using !!(expr) is pretty clear about the potential problem, and
> > generates no extra code if a bool is used for the target.
> 
> Though I don't think
> 	bool = expr;
> is particularly error prone,
> spatch shows 58 uses of
> 	bool = !!expr;
> in net-next drivers/net.
> 
> It might be useful to standardize on either the
> implicit or explicit !! style.
> 
> I think !! is an intentional and sensible style
> and should be the preferred use.

I see it as a workaround for the historical lack of a real bool type in
C.

> Perhaps a checkpatch warning should be issued
> when the implicit cast is used.

checkpatch can't do type-checking; maybe you mean sparse.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
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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