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Date: Tue, 1 Apr 2014 21:27:47 +0400
Message-ID: <CALYGNiONACddsH_6uaG5QyaWRaZ_5ZH0atZJyZVD=DowiKLJcw@mail.gmail.com>
Subject: Re: [PATCH RFC] drivers/char/mem: byte generating devices and
 poisoned mappings
From: Konstantin Khlebnikov <koct9i@gmail.com>
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To: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Hugh Dickins <hughd@google.com>, Yury Gribov <y.gribov@samsung.com>, Alexandr Andreev <aandreev@parallels.com>, Vassili Karpov <av1474@comtv.ru>, Andrew Morton <akpm@linux-foundation.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

On Tue, Apr 1, 2014 at 8:59 PM, One Thousand Gnomes
<gnomes@lxorguk.ukuu.org.uk> wrote:
> On Tue, 01 Apr 2014 01:16:07 +0400
> Konstantin Khlebnikov <koct9i@gmail.com> wrote:
>
>> This patch adds 256 virtual character devices: /dev/byte0, ..., /dev/byte255.
>> Each works like /dev/zero but generates memory filled with particular byte.
>
> More kernel code for an ultra-obscure corner case that can be done in
> user space
>
> I don't see the point

True. That was a long-planned joke.
But at the final moment I've found practical usage for it and overall
design became not such funny.

Currently I'm thinking about single-device model proposed by Kirill.

Let's call it /dev/poison. Application can open it, write a poison (up
to a page size) and after that this instance will generate pages
filled with this pattern. I don't see how this can be done in
userspace without major memory/cpu overhead caused by initial memset.

Default poison might be for example 0xff, so it still will be useful for 'dd'.

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