Re: [Xen-devel] suspend operation in XEND

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

> So when does the event channel between the backend & front end drivers
> break during suspend operation in XEND ??

The event channel itself will get destroyed when the domain is destroyed 
(after the domain's contents are saved).  From the guests PoV, no teardown of 
event channels or shared memory occurs before suspend - it all gets sorted 
out on resume.

> Also when is the NETIF_INTERFACE_STATUS_DISCONNECTED status sent to
> the front-end driver? I see code in the front-end driver that
> processes this status type which results in the front-driver going to
> a suspend state (like unregistering IRQs etc)

Interfaces go through various states.  During normal operation, these look 
like the following:
* DISCONNECTED -> CLOSED -> CONNECTED when an interface is attached to the 
domain
* CONNECTED -> CLOSED -> DISCONNECTED when an interface is removed.  In this 
case, the interface is in the CLOSED state when the DISCONNECTED message 
arrives, so this is the final disconnect for the interface

If the interface is in the CONNECTED state and a DISCONNECTED message is 
received, it means that the connection with the backend has been broken for 
some reason (e.g. the domain migrated to a new host, the backend driver 
domain was rebooted, etc).  When this happens, Xend will send this message to 
the domain.

If the guest sees this then it must go through the DISCONNECTED -> CLOSED -> 
CONNECTED transition again, talking on the control interface to set up shared 
memory and bind event channels with the new backend.  At this point, it also 
frees resources associated with the old device channel that are no longer 
needed (e.g. old IRQs).

HTH,
Mark

> On Thu, 20 Jan 2005 22:54:25 +0000, Mark Williamson <maw48@xxxxxxxxxxxx> 
wrote:
> > > During Save & Migration, XFRD sends "xfr.suspend" message to XEND.
> > > This results in XEND suspending the domainU. A part of the suspension
> > > should involve XEND sending DISCONNECT message to the front-end driver
> > > in domainU
> >
> > I don't think you'll find it.  Migrations / suspensions are treated like
> > a backend driver restart - at resume the frontend driver is notified that
> > it needs to reconnect to the backend and is responsible for requeuing any
> > pending requests.
> >
> > Instead of explicitly disconnecting the domain at suspend, the frontend
> > driver just sorts everything out at resume.
> >
> > Cheers,
> > Mark
> >
> > > I am trying to dig through the XEND python code & I am unable to find
> > > this information. Can someone help ??
> > >
> > > Also can someone guide me through the set of functions that are called
> > > by XEND as a part of suspend. What is the use of the the
> > > domain_restart_schedule() ??
> > >
> > > Thanks
> > >
> > > Nauzad
> > >
> > >
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