Hi,
On 03/15/2012 04:23 PM, Hans de Goede wrote:
Hi,
On 03/15/2012 03:07 PM, Yonit Halperin wrote:
Hi,
On 03/15/2012 02:36 PM, Hans de Goede wrote:
Hi,
On 03/15/2012 01:11 PM, Yonit Halperin wrote:
On 03/13/2012 09:40 AM, Gerd Hoffmann wrote:
Hi,
It is not easy when you have 2 components, and it is much less easy
when
you have 3 or 4 components. So why make it more complicated if you
can
avoid it. Especially since there is no functional reason for
making the
qemu/client capabilities/versions dependent on the server internal
data.
qemu has ways to handle compatibility in the vmstate format. We can
use
those capabilities. That of course requires exposing the structs to be
saved to qemu and adds some complexity to the qemu<-> spice interface.
What session state is needed by the target?
What of this can be negotiated between client and target host without
bothering the source?
What needs be transfered from source to target, either directly or via
client?
If this is a hard requirement then using the vmstate channel isn't
going
to work. The vmstate is a one-way channel, no way to negotiate
anything
between source and target.
We can do this via the client.
Then you can send the actual state via client too.
Out-of-band negotiation for the blob send via vmstate scares me.
Can we please start with a look at which state we actually have to
send
over?
Ok, I can take the display and sound channels.
Alon, can you take the smartcard?
Hans, spicevmc?
Easy, the spicevmc channel has no state which needs to be migrated,
except
for things in the red_channel_client base class:
1) Partially received spice messages
2) Possible pending pipe items when writes from qemu -> client have
blocked.
I assume that the red_channel_client base class will handle migrating
them,
if we migrate them at all.
Instead of migrating we could:
For 1. expect the client to stop sending new messages at a certain point
during the migration, and ensure we've processed any pending messages
after this point.
For 2. we could flush pending items and set a flag to stop channel
implementations from queuing new ones, at which point for spicevmc the
data will get queued inside qemu and migrating it no longer is
a spice-server problem to migrate it (and we need migration support for
the data possibly queued inside qemu anyways).
We have an implementation for this: After migration had completed,
each spice-server channel sent MSG_MIGRATE to the corresponding client
channel. The msg was sent after all the pending msgs to the client had
already been sent.
In response, the client sent SPICE_MSGC_MIGRATE_FLUSH_MARK to the
server, after it completed sending all its pending messages.
Yes, that is exactly what I thought we did but I was too lazy to check the
source :) So that would mean that other then assuring no data gets
queued up in spicevmc after sending the MSG_MIGRATE to the client (see
below),
no changes are needed to spicevmc, as it is essentially stateless.
Indeed, however, in order for this to work, we still need to make sure
the source qemu is not killed before we complete this.
Cheers,
Yonit.
Then the "blob" data transfer and completion of socket switching has
occurred.
Regarding the usb data in the server that should be flushed to qemu:
we need to save it after the source vm is stopped. So I think it is
too late for flushing it to qemu, unless you refereed to the special
vmstate we will have for spice, if we go in that solution direction.
I was talking about the other direction, so data queued in qemu which
should be flushed
to the server (and then forwarded to the client). IOW what I mean is that
after the spice-server channel sent MSG_MIGRATE, it should no longer
read data
from the qemu-chardev, even if it receives a chardev wakeup from qemu,
leaving the
data inside qemu to be migrated using qemu's standard migration mechanism.
Regards,
Hans
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