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Re: [Xen-devel] [PATCH] xen-blkfront: emit KOBJ_OFFLINE uevent when detaching device

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  Re: [Xen-devel] [PATCH] xen-blkfront: emit KOBJ_OFFLINE uevent when  detaching device Vincent Legout <vincent.legout@gandi.net> - 2017-09-05 09:40 +0200
    Re: [Xen-devel] [PATCH] xen-blkfront: emit KOBJ_OFFLINE uevent when  detaching device Juergen Gross <jgross@suse.com> - 2017-09-06 12:20 +0200
      Re: [Xen-devel] [PATCH] xen-blkfront: emit KOBJ_OFFLINE uevent when  detaching device Roger Pau Monné <roger.pau@citrix.com> - 2017-09-06 17:00 +0200

#1726485 — Re: [Xen-devel] [PATCH] xen-blkfront: emit KOBJ_OFFLINE uevent when detaching device

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Hello,

Sorry for such a long delay. I'm still interested in having this patch
merged.

I've tried to make the patch more generic and move it to xenbus as
discussed during the Xen summit, but I'm not sure how or if it's
possible. Would doing something in xenbus_otherend_changed() make sense?
But do we have enough information there? I'd be happy to get any advice,
I've re-attached the original patch.

On Fri, Jul 07, 2017 at 09:10:53AM +0100, Roger Pau Monné wrote :
> On Wed, Jul 05, 2017 at 03:30:00PM +0200, Vincent Legout wrote:
> > On Wed, Jul 05, 2017 at 06:53:25AM -0600, Jan Beulich wrote :
> > > >>> On 05.07.17 at 14:37, <vincent.legout@gandi.net> wrote:
> > > > On Wed, Jul 05, 2017 at 02:17:24AM -0600, Jan Beulich wrote :
> > > >> >>> On 05.07.17 at 10:08, <vincent.legout@gandi.net> wrote:
> > > >> > Without the patch, blkif_release and xlvbd_release_gendisk are never
> > > >> > called, and no call to blk_unregister_queue is made.
> > > >> 
> > > >> But isn't that what needs to be fixed then? The device should be
> > > >> removed once its last user goes away (which would be at the time
> > > >> the umount is eventually done aiui).
> > > > 
> > > > You mean that block-detach should fail if the device is still mounted?
> > > > or find a way to wait until all the users are gone?
> > > > 
> > > > I don't say that's not what should be done, but that's not what I get.
> > > > The device is removed after a block-detach, even if still mounted. So
> > > > the system is left in an unstable state without the patch.
> > > 
> > > Unstable? I'd expect subsequent I/O to fail for that device, yes, but
> > > that's still a stable system. Are you observing anything else?
> > 
> > Yes, that's what I meant by unstable, nothing else. Sorry for the
> > confusion.
> 
> IMHO, this should behave in the same exact way as hot-unplugging a USB
> drive that's mounted, can you confirm that's correct?

I agree. And if I'm not wrong, it currently doesn't behave the same as
USB device unplugging. The patch tries to fix that.

Thanks,
Vincent

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#1727316

On 05/09/17 09:28, Vincent Legout wrote:
> Hello,
> 
> Sorry for such a long delay. I'm still interested in having this patch
> merged.
> 
> I've tried to make the patch more generic and move it to xenbus as
> discussed during the Xen summit, but I'm not sure how or if it's
> possible. Would doing something in xenbus_otherend_changed() make sense?
> But do we have enough information there? I'd be happy to get any advice,
> I've re-attached the original patch.

Maybe you could add a callback to struct xenbus_driver which is called
by xenbus_otherend_changed() if available and which will return the
missing information (e.g. the kobj).


Juergen

> 
> On Fri, Jul 07, 2017 at 09:10:53AM +0100, Roger Pau Monné wrote :
>> On Wed, Jul 05, 2017 at 03:30:00PM +0200, Vincent Legout wrote:
>>> On Wed, Jul 05, 2017 at 06:53:25AM -0600, Jan Beulich wrote :
>>>>>>> On 05.07.17 at 14:37, <vincent.legout@gandi.net> wrote:
>>>>> On Wed, Jul 05, 2017 at 02:17:24AM -0600, Jan Beulich wrote :
>>>>>>>>> On 05.07.17 at 10:08, <vincent.legout@gandi.net> wrote:
>>>>>>> Without the patch, blkif_release and xlvbd_release_gendisk are never
>>>>>>> called, and no call to blk_unregister_queue is made.
>>>>>>
>>>>>> But isn't that what needs to be fixed then? The device should be
>>>>>> removed once its last user goes away (which would be at the time
>>>>>> the umount is eventually done aiui).
>>>>>
>>>>> You mean that block-detach should fail if the device is still mounted?
>>>>> or find a way to wait until all the users are gone?
>>>>>
>>>>> I don't say that's not what should be done, but that's not what I get.
>>>>> The device is removed after a block-detach, even if still mounted. So
>>>>> the system is left in an unstable state without the patch.
>>>>
>>>> Unstable? I'd expect subsequent I/O to fail for that device, yes, but
>>>> that's still a stable system. Are you observing anything else?
>>>
>>> Yes, that's what I meant by unstable, nothing else. Sorry for the
>>> confusion.
>>
>> IMHO, this should behave in the same exact way as hot-unplugging a USB
>> drive that's mounted, can you confirm that's correct?
> 
> I agree. And if I'm not wrong, it currently doesn't behave the same as
> USB device unplugging. The patch tries to fix that.
> 
> Thanks,
> Vincent
> 

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#1727569

On Wed, Sep 06, 2017 at 12:18:03PM +0200, Juergen Gross wrote:
> On 05/09/17 09:28, Vincent Legout wrote:
> > Hello,
> > 
> > Sorry for such a long delay. I'm still interested in having this patch
> > merged.
> > 
> > I've tried to make the patch more generic and move it to xenbus as
> > discussed during the Xen summit, but I'm not sure how or if it's
> > possible. Would doing something in xenbus_otherend_changed() make sense?
> > But do we have enough information there? I'd be happy to get any advice,
> > I've re-attached the original patch.
> 
> Maybe you could add a callback to struct xenbus_driver which is called
> by xenbus_otherend_changed() if available and which will return the
> missing information (e.g. the kobj).

Hello,

I'm still unsure we should call KOBJ_OFFLINE, mostly because I don't
see any other block devices doing so. AFAICT it seems to be used only
by cpu and memory hotplug. Maybe xenbus should use the device_offline
function instead on each device it wants to remove?

From my limited Linux bus handling understanding, this seems to be
more in line with what ACPI does for example.

Thanks, Roger.

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