linux-kernel - Re: [Xen-devel] [PATCH] xen-blkfront: emit KOBJ

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Date:   Wed, 6 Sep 2017 12:18:03 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Vincent Legout <vincent.legout@...di.net>,
        Roger Pau Monné <roger.pau@...rix.com>
Cc:     Jan Beulich <JBeulich@...e.com>, xen-devel@...ts.xenproject.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] [PATCH] xen-blkfront: emit KOBJ_OFFLINE uevent when
 detaching device

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@...di.net> wrote:
>>>>> On Wed, Jul 05, 2017 at 02:17:24AM -0600, Jan Beulich wrote :
>>>>>>>>> On 05.07.17 at 10:08, <vincent.legout@...di.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
>