linux-kernel - Re: [PATCH 3/3] staging/ozwpan: coding style ether_addr

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Message-ID: <1396012107.31134.21.camel@joe-AO722>
Date:	Fri, 28 Mar 2014 06:08:27 -0700
From:	Joe Perches <joe@...ches.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Jérôme Pinot <ngc891@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org, Chris Kelly <ckelly@...odevices.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] staging/ozwpan: coding style ether_addr_copy

(adding Andrew Morton, David Miller and LKML to cc's)

On Fri, 2014-03-28 at 14:18 +0300, Dan Carpenter wrote:
> On Fri, Mar 14, 2014 at 12:39:11AM +0900, Jérôme Pinot wrote:
> > On 03/13/14 02:28, Greg Kroah-Hartman wrote:
> > > On Thu, Mar 13, 2014 at 10:21:44AM +0900, Jérôme Pinot wrote:
> > [...]
> > > > diff --git a/drivers/staging/ozwpan/ozcdev.c b/drivers/staging/ozwpan/ozcdev.c
> > > > index 5de5981..10c0a96 100644
> > > > --- a/drivers/staging/ozwpan/ozcdev.c
> > > > +++ b/drivers/staging/ozwpan/ozcdev.c
> > > > @@ -217,7 +217,7 @@ static int oz_set_active_pd(const u8 *addr)
> > > >  	pd = oz_pd_find(addr);
> > > >  	if (pd) {
> > > >  		spin_lock_bh(&g_cdev.lock);
> > > > -		memcpy(g_cdev.active_addr, addr, ETH_ALEN);
> > > > +		ether_addr_copy(g_cdev.active_addr, addr);
> > > 
> > > Are you sure this will work?
> > 
> > No. But the ozwpan driver uses already ether_addr_equal which is not
> > alignment-safe. As
> > https://www.kernel.org/doc/Documentation/unaligned-memory-access.txt 
> > said:
> > 
> > "This alignment-unsafe function is still useful as it is a decent
> > optimization for the cases when you can ensure alignment, which is
> > true almost all of the time in ethernet networking context."
> > 
> > I expected the maintainer to confirm/infirm this. I'm just seeing that's
> > actually Chris Kelly who did write this part of code, so I'm CC'ing him
> > too.
> > 
> 
> It is aligned ok, but don't rely on the maintainer to fix your bugs.
> Don't send patches which you are not sure about.
> 
> Joe, this seems like a very bad warning message from checkpatch.pl
> because people will constantly send us patches over and over which
> introduce bugs and they rely on the maintainer to catch it every time.
> Can we get rid of the warning or move it under --strict or something?

Hi Dan.

Maybe.

The checkpatch message is:

"Prefer ether_addr_copy() over memcpy() if the Ethernet addresses are __aligned(2)"

My personal preference would be to add YA inline function
for unaligned copies ether_addr_copy_unaligned for symmetry
to ether_addr_equal_unaligned to etherdevice.h though.

Then the message could be changed to something like
"Prefer ether_addr_copy[_unaligned] to memcpy(foo, bar, ETH_ALEN)"

> Do we have a mailing list yet for checkpatch issues?

No and I'm not going to advocate for one. I think the
subscriber count would be about 4 people total.

You could add yourself to the checkpatch MAINTAINERS entry
if you want to see more of the patches and discussions.

They are pretty rare.

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