linux-kernel - Re: [systemd-devel] Suspending access to opened/active /dev/nodes during application runtime

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Message-Id: <93871091-7845-4BCC-A841-F724BEDF6E4B@gmail.com>
Date:	Fri, 7 Mar 2014 21:45:28 +0100
From:	Lukasz Pawelczyk <havner@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	libvir-list@...hat.com, lxc-devel@...ts.linuxcontainers.org,
	systemd-devel@...ts.freedesktop.org,
	David Herrmann <dh.herrmann@...il.com>
Subject: Re: [systemd-devel] Suspending access to opened/active /dev/nodes during application runtime


On 7 Mar 2014, at 20:09, Greg KH <gregkh@...uxfoundation.org> wrote:

> On Fri, Mar 07, 2014 at 07:46:44PM +0100, Lukasz Pawelczyk wrote:
>> Problem:
>> Has anyone thought about a mechanism to limit/remove an access to a
>> device during an application runtime? Meaning we have an application
>> that has an open file descriptor to some /dev/node and depending on
>> *something* it gains or looses the access to it gracefully (with or
>> without a notification, but without any fatal consequences).
>> 
>> Example:
>> LXC. Imagine we have 2 separate containers. Both running full operating
>> systems. Specifically with 2 X servers. Both running concurrently of
>> course. Both need the same input devices (e.g. we have just one mouse).
> 
> Stop right there.
> 
> If they "both" need an input device, then they should use the "shared"
> input device stream, i.e. evdev.
> 
> And it goes the same for every type of device the kernel is exposing to
> userspace, if you want to "share" them, then you need to work on
> changing the kernel to be able to handle shared devices.

I think you might have misunderstood me. They are using a shared input stream (evdev in this case). The problem is I don’t want them to eavesdrop on each other. So it’s not about making it to work. It’s about making them to work „in turns”.

> And odds are, you will get back a big "as-if" comment from the kernel
> developers, as for almost all devices, they can't be shared, for very
> good reasons.

Evdev devices can.


-- 
Regards,
Havner



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