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Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migrati
From: |
Anthony Liguori |
Subject: |
Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration |
Date: |
Wed, 27 Jul 2011 09:16:33 -0500 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110516 Lightning/1.0b2 Thunderbird/3.1.10 |
On 07/27/2011 02:07 AM, Alon Levy wrote:
On Wed, Jul 27, 2011 at 07:45:25AM +0200, Markus Armbruster wrote:
Alon Levy<address@hidden> writes:
Signed-off-by: Alon Levy<address@hidden>
---
hw/virtio-serial-bus.c | 8 +++++++-
1 files changed, 7 insertions(+), 1 deletions(-)
diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index c5eb931..7a652ff 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -618,14 +618,20 @@ static int virtio_serial_load(QEMUFile *f, void *opaque,
int version_id)
for (i = 0; i< nr_active_ports; i++) {
uint32_t id;
bool host_connected;
+ VirtIOSerialPortInfo *info;
id = qemu_get_be32(f);
port = find_port_by_id(s, id);
if (!port) {
return -EINVAL;
}
-
port->guest_connected = qemu_get_byte(f);
+ info = DO_UPCAST(VirtIOSerialPortInfo, qdev, port->dev.info);
+ if (port->guest_connected&& info->guest_open) {
+ /* replay guest open */
+ info->guest_open(port);
+
+ }
host_connected = qemu_get_byte(f);
if (host_connected != port->host_connected) {
/*
The patch makes enough sense to me, but the commit message is
insufficient. Why do you have to replay? And what's being fixed?
When migrating a host with with a spice agent running the mouse becomes
non operational after the migration. This is rhbz #718463, currently on
spice-server but it seems this is a qemu-kvm issue. The problem is that
after migration spice doesn't know the guest agent is open.
The problem is that guest_open is a hack.
You want connection semantics. You need the following information from
the backend and the client:
1) backend is associated with a transport. The transport may disconnect
at any point in time. The backend needs to have explicit state
transitions associated with the transport disconnecting and connecting.
2) the client may disconnect and reconnect at any point in time. A
device model reset is a disconnect followed by a reconnect.
This gives you the following matrix of states:
A: backend-connected, client-connected
B: backend-disconnected, client-disconnected
C: backend-connected, client-disconnected
D: backend-disconnected, client-connected
The state transition diagram looks like this:
B: for some devices, immediately goto C. other devices, on accept()
goto D. if in B and client connects, goto D
C: if transport disconnects, goto B. if client connects, goto A
D: if transport connects, goto A. if client disconects, goto B
A: if transport disconnects, goto B, if client disconnects, goto C
The problem is that guest_open() is a poor approximation of
'client-connected' and it's not used universally. We need to introduce
proper state tracking to the character device layer and we need to have
a proper connection function that is used by all char device clients.
Semantically, write should only be allowed in states A and D. Read
should only be allowed in states A and C.
C and D should have very well defined semantics about what happens to
the data that is written Arguably, read/write should not be allowed in
states C/D.
Device reset should always trigger a client reconnect. Migration resets
devices so migration would Just Work if we modelled the state
transitions appropriately.
Regards,
Anthony Liguori
- [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, 2011/07/27
- Re: [Qemu-devel] [PATCH] virtio-serial-bus: replay guest_open on migration,
Anthony Liguori <=
- 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