linux-kernel - Re: [PATCH v2 5/5] Input: evdev

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Date:   Mon, 18 Jun 2018 08:49:37 -0700
From:   Joe Perches <joe@...ches.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Yury Norov <ynorov@...iumnetworks.com>
Cc:     agk@...hat.com, Mike Snitzer <snitzer@...hat.com>,
        dm-devel@...hat.com, shli@...nel.org, linux-raid@...r.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        linux-input <linux-input@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH v2 5/5] Input: evdev - Switch to bitmap_zalloc()

On Mon, 2018-06-18 at 15:02 +0300, Andy Shevchenko wrote:
> On Sat, 2018-06-16 at 12:16 -0700, Joe Perches wrote:
> > On Sat, 2018-06-16 at 21:45 +0300, Andy Shevchenko wrote:
> > > On Sat, Jun 16, 2018 at 12:46 AM Yury Norov <ynorov@...iumnetworks.c
> > > om> wrote:
> > > > On Fri, Jun 15, 2018 at 04:20:17PM +0300, Andy Shevchenko wrote:
> > > > > Switch to bitmap_zalloc() to show clearly what we are
> > > > > allocating.
> > > > > Besides that it returns pointer of bitmap type instead of opaque
> > > > > void *.
> > > 
> > > 
> > > > > +       mem = bitmap_alloc(maxbit, GFP_KERNEL);
> > > > >         if (!mem)
> > > > >                 return -ENOMEM;
> > > > 
> > > > But in commit message you say you switch to bitmap_zalloc(). IIUC
> > > > bitmap_alloc() is OK here. But could you please update comment to
> > > > avoid confusing.
> > > 
> > > There are two places, one with alloc, another with zalloc.
> > > I will clarify this in commit message of next version.
> > > 
> > > > > +       mask = bitmap_zalloc(cnt, GFP_KERNEL);
> > > > >         if (!mask)
> > > > >                 return -ENOMEM;
> > > > > 
> > > > >         error = bits_from_user(mask, cnt - 1, codes_size, codes,
> > > > > compat);
> > > > 
> > > > If my understanding of bits_from_user() correct, here you can also
> > > > use
> > > > bitmap_alloc(), true?
> > 
> > Also it might be useful to have a separate bitmap_from_user
> > to alloc and copy.
> 
> Maybe. I didn't check if there are such users except this driver.
> 
> Anyway, it's out of scope of the series.

That seems incorrect as you are introducing alloc/free helpers.

Perhaps bitmap_dup_user [or some better name] could or should
be one of the helpers.