[Devel] Re: kernel based checkpoint/restart: about X windows application checkpoint and restart support.

[Oren Laadan]

Matt Helsley wrote:
> On Wed, Oct 28, 2009 at 11:02:43AM -0400, Oren Laadan wrote:
>>
>> Matt Helsley wrote:
>>> On Wed, Oct 28, 2009 at 10:51:32AM +0800, Will Huang wrote:
>>>> Dear All,
>>>>
>>>>          Did the Kernel based checkpoint/restart patch support X windows
>>>> application such as firefox?
>>> No, and I think it may be a long time before that happens.
>> In short: not yet, but we're getting closer.
>>
> 
> <snip> (lots of good background)
>  
>> Now back to your question: X applications cannot be checkpointed
>> standalone (unless, of course, X windows is modified for that).
>> Instead, one must checkpoint the entire user session, including
>> the X server itself.
>>
>> The main problem is that the X server is "talking" to the bare
>> hardware, and the task of recording the specific hardware state
>> and restoring it later is daunting, and becomes impossible if the
>> session is to be restarted on different hardware.
>>
>> The solution is to not run the regular X server. Instead, start
>> a virtual X server, such as VNC, and run the user session in it.
>> The main difference is that VNC server does not directly use any
>> hardware resources, so it is not tied to specific hardware state.
>> From the user's point of view - this setup is transparent with
>> suitable use of a VNC client.
> 
> VNC is all well and good but it's hardly the norm for local
> desktops to run under an X server with a VNC display. That said,
> VNC support is much closer than any of my hare-brained ideas so..

There is a lot of work on server/client split of the X server
(of which VNC is one), and also work on embedding one display
manager within another (e.g. nested X, and also similar ideas
done with embedding a VM window in the desktop as a regular
window etc).

So eventually, I believe, embedding a (virtualized) X server in
an outside X server and running the entire desktop in a container
will eventually be possible in a manner transparent to the user.

And this is much more likely than checkpoint the standard X
server including all it's hardware related state...

Changing the norm starts now :)

Oren.

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