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Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migrati
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration |
Date: |
Wed, 27 Jul 2011 16:02:01 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) |
Alon Levy <address@hidden> writes:
> On Wed, Jul 27, 2011 at 05:35:28PM +0530, Amit Shah wrote:
>> On (Wed) 27 Jul 2011 [14:09:45], Alon Levy wrote:
>>
>> > > Also, we'll be lying that a guest opened, since a guest was opened
>> > > much earlier, before migration. Nothing has changed as far as the
>> > > guest is concerned, this is just some host-side tracking that has to
>> > > be done post-migrate, which belongs in individual devices / ports.
>> >
>> > The callback is there on purpose, some qemu side users exist surely. While
>> > I understand the lying part about the time, it is worst to lie completely
>> > by not mentioning the guest has opened the port.
>>
>> Guest has not re-opened the port. When the guest opened the port,
>> spice did get the callback called. After migration, guest state has
>> not changed. Why should you get the callback again?
> Again, my point is that from the chardev pov this *is* the first callback.
> You say the timing is wrong - correct, but I don't see any part in the api
> that talks about timing, i.e. no gurantee to be broken.
>
> Actually searching for current users it appears it is just spicevmc
> (spice-qemu-char.c).
>
>> If you depend on
>> guest connectedness, after migration, just ensure you do whatever is
>> necessary. I think there's no need to involve any other code in this.
>
> There is no migration mechanism for char devices. There is no migration
> mechanism for the spice server. All data that is passed is done via device
> migration -
> qxl or in this case I suggest virtio-serial.
>
> Do you think chardevices should be migratable? that would also work.
No.
We migrate device models (frontends). The backends get recreated from
scratch.
> Do you think a separate callback would be better worded? or add a "migrated"
> boolean?
> both are ugly, I agree.
I don't see the need for two separate callbacks. From the backend's
point of view, there's no difference between normal startup and
migration startup.
If the name "guest_open" bothers you, find another one. guest_connect?
The guest (or rather the device model), connects to a newly created
backend chrdev. The just guest doesn't know it (the device model does).
> The chardev does receive parameters, it's possible to have the remote vm
> start with
> a spicevmc chardev that has "migrated=1" as part of the command line. That
> looks much
> uglier then this patch to me.
There's no precedence for "migrated=1".
For what it's worth, my recent block layer series also has device models
run backend callbacks after migration. Check out "[PATCH 37/55]
ide/atapi: Preserve tray state on migration" and "[PATCH 38/55]
scsi-disk: Preserve tray state on migration".
- [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Alon Levy, 2011/07/26
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Markus Armbruster, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Alon Levy, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Markus Armbruster, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Amit Shah, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Alon Levy, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Amit Shah, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Alon Levy, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration,
Markus Armbruster <=
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Anthony Liguori, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Alon Levy, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Anthony Liguori, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration, Alon Levy, 2011/07/27