Re: Re: Hotplug events during sleep transition

[Dmitry Torokhov <dtor_core@ameritech.net>]

On Tuesday 27 December 2005 23:36, Patrick Mochel wrote:
> 
> On Tue, 27 Dec 2005, Dmitry Torokhov wrote:
> 
> > On 12/27/05, Patrick Mochel <mochel@digitalimplant.org> wrote:
> 
> > > Would it be possible to simply mark the device as 'removed' and ignore it
> > > until we resumed, and then clean it up (hotplug events and everything)?
> > >
> >
> > Unfortunately swsusp resumes devices in the middle of suspend process
> > with everything frozen and drivers don't know if they may clean up or
> > have to postpone doing so. To do it uniformly you'd need to introduce
> > threads and offload cleanups. I doubt it is good idea to require each
> > subsystem to define cleanup thread or [ab]used keventd?
> 
> Blech, I forgot about the caveman-like way of making sure the swap device
> is resumed. :)
> 
> Nevertheless, it shouldn't matter, and you bring up a point that exists,
> and is actually more prevalent - the case of trying to resume a device
> that doesn't exist any more.
> 
> Last week, I suggested that all devices that are thought to be present
> should be resumed. Those that have gone away should be removed once the
> system is resumed, then new devices should be discovered. In this, I am
> implying that devices that are thought to be there, but really aren't
> (have been removed, unplugged, or undocked) should be marked as such
> (somehow) and taken care of later.
> 
> When swsusp resumes every device before writing the image, it should
> ignore devices that aren't present anymore. They can still exist in
> software (in the various object hiearchies), but they should just be
> skipped. Ditto for when we 'suspend' them again, and on the real resume.
> 
> When the system is back up and userspace is started again, something
> should walk the device tree and reap the devices that are no longer
> present. The core could do this, so long as the flag was in struct device,
> though I'm not sure that it would know about the hooks to trigger a
> removal on the device's bus (or would it need to?). Then, we can free all
> the memory, do all the unregistering, and generate all the hotplug events.
> 
> Of course, at that point, we'll need to discover any new devices, which is
> going to be bus-speciifc. But, with a few extra bits of infrastructure
> (per-bus objects, and a ->scan() method in struct bus_type), this will
> relatively simple..
> 
> Thoughts?
> 

I suppose... New devices will indeed have to be bus-specific but reaping
function I think can be same for everyone - just call device_unregister()
for every device that is marked as 'dead'. Unregister usually ignores all
errors anyway.

-- 
Dmitry