Subject: Re: [PATCH v3 2/2] staging: ion: create one device entry per heap
To: Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        sumit.semwal@linaro.org, gregkh@linuxfoundation.org, arve@android.com,
        riandrews@android.com, broonie@kernel.org, dan.carpenter@oracle.com
Cc: devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org
References: <1505897105-23721-1-git-send-email-benjamin.gaignard@linaro.org>
 <1505897105-23721-3-git-send-email-benjamin.gaignard@linaro.org>
From: Laura Abbott <labbott@redhat.com>
Message-ID: <3dbd167f-c381-8451-5861-3788634885b7@redhat.com>
Date: Mon, 25 Sep 2017 11:26:27 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.2.0
MIME-Version: 1.0
In-Reply-To: <1505897105-23721-3-git-send-email-benjamin.gaignard@linaro.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1134
Lines: 29

On 09/20/2017 01:45 AM, Benjamin Gaignard wrote:
> Instead a getting one common device "/dev/ion" for
> all the heaps this patch allow to create one device
> entry ("/dev/ionX") per heap.
> Getting an entry per heap could allow to set security rules
> per heap and global ones for all heaps.
> 
> Allocation requests will be only allowed if the mask_id
> match with device minor.
> Query request could be done on any of the devices.
> Deivce node major will also change and that may impact init scripts.
> 

We should start Cc linux-api for future changes since we're going
to have more than just /dev/ion.

Thinking about this some more, I think we need to allow backwards
compatibility. It's just not feasible to keep throwing workarounds
into userspace if we can avoid it. I'd propose keeping the old /dev/ion
misc interface available under a Kconfig and then creating the new
split heaps in parallel.

On a somewhat related note, there was some interest in possibly
having a sysfs interface for Ion long term. I don't think this
needs to happen right now but I'd like whatever we do to not
make adding that harder.

Thanks,
Laura