From: John Snow <jsnow@redhat.com>
To: Paul Durrant <Paul.Durrant@citrix.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"qemu-block@nongnu.org" <qemu-block@nongnu.org>
Cc: Kevin Wolf <kwolf@redhat.com>,
Anthony Perard <anthony.perard@citrix.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Mark Syms <Mark.Syms@citrix.com>, Max Reitz <mreitz@redhat.com>
Subject: Re: [Qemu-block] [PATCH] xen-block: treat XenbusStateUnknown the same as XenbusStateClosed
Date: Mon, 23 Sep 2019 13:08:43 -0400 [thread overview]
Message-ID: <466c855c-e962-2473-27db-0a019938d1f6@redhat.com> (raw)
In-Reply-To: <46f838982f7d448b86391bc48e9d8179@AMSPEX02CL03.citrite.net>
On 9/23/19 5:38 AM, Paul Durrant wrote:
>> -----Original Message-----
>> From: John Snow <jsnow@redhat.com>
>> Sent: 20 September 2019 22:11
>> To: Paul Durrant <Paul.Durrant@citrix.com>; xen-devel@lists.xenproject.org; qemu-devel@nongnu.org;
>> qemu-block@nongnu.org
>> Cc: Kevin Wolf <kwolf@redhat.com>; Stefano Stabellini <sstabellini@kernel.org>; Max Reitz
>> <mreitz@redhat.com>; Anthony Perard <anthony.perard@citrix.com>; Mark Syms <Mark.Syms@citrix.com>
>> Subject: Re: [Qemu-block] [PATCH] xen-block: treat XenbusStateUnknown the same as XenbusStateClosed
>>
>>
>>
>> On 9/18/19 7:57 AM, Paul Durrant wrote:
>>> When a frontend gracefully disconnects from an offline backend, it will
>>> set its own state to XenbusStateClosed. The code in xen-block.c correctly
>>> deals with this and sets the backend into XenbusStateClosed. Unfortunately
>>> it is possible for toolstack to actually delete the frontend area
>>> before the state key has been read, leading to an apparent frontend state
>>> of XenbusStateUnknown. This prevents the backend state from transitioning
>>> to XenbusStateClosed and hence leaves it limbo.
>>>
>>
>> Does the 0 come from a read into de-allocated memory?
>
> No, it comes from the fact that the xenstore state key is not present. Conventionally a missing state key means the state is reported as XenbusStateUnknown.
>
> Paul
>
Good enough for me, just had to confirm.
Reviewed-by: John Snow <jsnow@redhat.com>
next prev parent reply other threads:[~2019-09-23 17:09 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-18 11:57 [Qemu-devel] [PATCH] xen-block: treat XenbusStateUnknown the same as XenbusStateClosed Paul Durrant
2019-09-20 21:10 ` [Qemu-block] " John Snow
2019-09-23 9:38 ` Paul Durrant
2019-09-23 17:08 ` John Snow [this message]
2019-09-23 11:34 ` Anthony PERARD
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