Re: A udev rule to serve the change event of ACPI container?

[joeyli]

Hi Michal, 

Sorry for my delay.

On Tue, Jul 11, 2017 at 10:25:32AM +0200, Michal Hocko wrote:
> On Mon 26-06-17 10:59:07, Michal Hocko wrote:
> > On Mon 26-06-17 14:26:57, Joey Lee wrote:
> > > Hi all,
> > > 
> > > If ACPI received ejection request for a ACPI container, kernel
> > > emits KOBJ_CHANGE uevent when it found online children devices
> > > below the acpi container.
> > > 
> > > Base on the description of caa73ea15 kernel patch, user space
> > > is expected to offline all devices below the container and the
> > > container itself. Then, user space can finalize the removal of
> > > the container with the help of its ACPI device object's eject
> > > attribute in sysfs.
> > > 
> > > That means that kernel relies on users space to peform the offline
> > > and ejection jobs to acpi container and children devices. The
> > > discussion is here:
> > > 	https://lkml.org/lkml/2013/11/28/520
> > > 
> > > The mail loop didn't explain why the userspace is responsible for
> > > the whole container offlining. Is it possible to do that transparently
> > > from the kernel? What's the difference between offlining memory and
> > > processors which happends without any cleanup and container which
> > > does essentially the same except it happens at once? 
> > >  
> > >  - After a couple of years, can we let the container hot-remove
> > >    process transparently?
> > >  - Except udev rule, does there have any other mechanism to trigger
> > >    auto offline/ejection?
> > 
> > I would be also interested whether the kernel can simply send an udev event
> > to all devices in the container.
> 
> Any opinion on this?

If BIOS emits ejection event for a ACPI0004 container, someone needs
to handle the offline/eject jobs of container. Either kernel or user
space.

Only sending uevent to individual child device can simplify udev rule,
but it also means that the kernel needs to offline/eject container
after all children devices are offlined. Maybe adding a ejection flag
on the ACPI0004 object to indicate the container state. But, if userland
doesn't do his job, then the timing to reset the flag will be the problem. 

Thanks a lot!
Joey Lee