linux-kernel - RE: [PATCH] intel: i40e: fix confused code

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Message-ID: <FC41C24E35F18A40888AACA1A36F3E418AFA5229@fmsmsx115.amr.corp.intel.com>
Date:	Tue, 20 Oct 2015 15:27:12 +0000
From:	"Nelson, Shannon" <shannon.nelson@...el.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
CC:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	"Wyborny, Carolyn" <carolyn.wyborny@...el.com>,
	"Skidmore, Donald C" <donald.c.skidmore@...el.com>,
	"Vick, Matthew" <matthew.vick@...el.com>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"Williams, Mitch A" <mitch.a.williams@...el.com>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] intel: i40e: fix confused code

> From: Rasmus Villemoes [mailto:linux@...musvillemoes.dk]
> Sent: Tuesday, October 20, 2015 12:22 AM
> 
> On Mon, Oct 19 2015, "Nelson, Shannon" <shannon.nelson@...el.com> wrote:
> 
> >> From: Rasmus Villemoes [mailto:linux@...musvillemoes.dk]
> >> Sent: Saturday, October 17, 2015 1:58 PM
> >> Subject: [PATCH] intel: i40e: fix confused code
> >>
> >> This code is pretty confused. The variable name 'bytes_not_copied'
> >> clearly indicates that the programmer knew the semantics of
> >> copy_{to,from}_user, but then the return value is checked for being
> >> negative and used as a -Exxx return value.
> >>
> >> I'm not sure this is the proper fix, but at least we get rid of the
> >> dead code which pretended to check for access faults.
> >>
> >> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> >
> > I believe this patch is unnecessary: if the value is negative, then it
> > already is an error code giving some potentially useful information.
> > When I dig into the copy_to_user() code, I see in the comments for
> > put_user() that -EFAULT is the error being returned.
> 
> Thanks, this was precisely the kind of confusion I'm talking about:
> copy_{from,to}_user _never_ returns a negative value. It returns
> precisely what the very explicit variable name hints.
> 
> This is in contrast to the single-scalar functions get_user/put_user,
> which do return -EFAULT for error and 0 for success.
> 
> (See also lines 479-519 of Documentation/DocBook/kernel-hacking.tmpl).

I like the comment about the moronic interface for copy_to/from_user...

Yes, I see where I turned left instead of right.  This would be good to fix up.

sln
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