[vdsm] Review Request: Add an option to create a watchdog device.

[Doron Fediuck]

----- Original Message -----
> From: "Ryan Harper" <ryanh at us.ibm.com>
> To: "Doron Fediuck" <dfediuck at redhat.com>
> Cc: "Sheldon" <shaohef at linux.vnet.ibm.com>, arch at ovirt.org, "Zheng Sheng ZS Zhou" <zhshzhou at cn.ibm.com>, "Itamar
> Heim" <iheim at redhat.com>, agl at linux.vnet.ibm.com, "Shu Ming" <shuming at linux.vnet.ibm.com>, "Mark Wu"
> <wudxw at linux.vnet.ibm.com>, ryanh at us.ibm.com, snmishra at us.ibm.com, danken at redhat.com
> Sent: Monday, November 26, 2012 4:01:48 PM
> Subject: Re: [vdsm] Review Request: Add an option to create a watchdog device.
> 
> * Doron Fediuck <dfediuck at redhat.com> [2012-11-22 03:56]:
> > 
> > ----- Original Message -----
> > 
> > > From: "Sheldon" <shaohef at linux.vnet.ibm.com>
> > > To: "Doron Fediuck" <dfediuck at redhat.com>
> > > Cc: arch at ovirt.org, "Zheng Sheng ZS Zhou" <zhshzhou at cn.ibm.com>,
> > > "Itamar Heim" <iheim at redhat.com>, agl at linux.vnet.ibm.com, "Shu
> > > Ming"
> > > <shuming at linux.vnet.ibm.com>, "Mark Wu"
> > > <wudxw at linux.vnet.ibm.com>,
> > > ryanh at us.ibm.com, snmishra at us.ibm.com, danken at redhat.com
> > > Sent: Thursday, November 22, 2012 11:00:18 AM
> > > Subject: Re: [vdsm] Review Request: Add an option to create a
> > > watchdog device.
> > 
> > > On 11/21/2012 04:00 PM, Doron Fediuck wrote:
> > 
> > > > > Currently, we do not have any plans to implement the engine
> > > > > side
> > > > > of
> > > > > the feature.
> > > > 
> > > 
> > > > > But I will add a watchdog feature page to describe how engine
> > > > > enable
> > > > > this feature. It's definitely great if any engine guy would
> > > > > like
> > > > > to
> > > > > take the engine part. I will be glad to provide help if
> > > > > needed.
> > > > 
> > > 
> > > > Hi Sheldon,
> > > 
> > > > Any news on the engine side?
> > > 
> > > > Currently the vdsm side is merged, while the engine side still
> > > > missing.
> > > 
> > > > The wiki page also lacks the engine side. Can you please handle
> > > > it?
> > > 
> > 
> > > Hi Doron,
> > 
> > > I have updated the wiki page.
> > > http://wiki.ovirt.org/wiki/Add_an_option_to_create_a_watchdog_device
> > > And for vdsm side, I should also add a new patch to report the
> > > watchdog event.
> > 
> > > I can add a flat to vm's status, so engine can poll vm's status
> > > to
> > > check the event then notify the user, and let the user to take
> > > some
> > > actions, such as restart or dump guest for analysis.
> > > Perhaps event report channel is more better, but I have not find
> > > any
> > > in vdsm. But it is a big work to add an event register mechanism
> > > for
> > > vdsm.
> > 
> > > what's your suggestion?
> > 
> > > --
> > > Sheldon Feng(?????????) <shaohef at linux.vnet.ibm.com> IBM Linux
> > > Technology
> > > Center
> > 
> > Hi Sheldon,
> > AFAIK, watchdog fires automatically, so no real need for user
> > interaction
> > when an event happens. So I'd expect the user to set the relevant
> > action
> > before starting the VM. Once the watchdog is triggered, it will do
> > whatever
> > action he has set, and notify the user.
> > 
> > So I'd expect the user to have a list of actions for the watchdog
> > device
> > in the engine UI, with a default of none. The user should be able
> > to choose
> > which action to set when starting or editing the VM (for next run).
> 
> I'd like to suggest we pick something other than none by default
> since
> we've gone through the trouble of configuring and enabling a
> watchdog.
> I think it's worth the discussion of what a better default behavior
> should be given access to a watchdog.
> 
> I'd suggest that a simple reboot mode would be most useful.
> 

Hi Ryan, good point.
The reason I asked for none is exactly since someone though of it
when writing the device actions. ie- otherwise no-op makes no sense,
but as we all know no-op sometimes proves to be a much needed option
if not the default one.
In this context, a watchdog has quite an explosive potential for a VM.
So for the sake of all users I'd rather ask them to specify exactly
what should be done. Otherwise- Primum non nocere. I'm sure one day
someone will appreciate it.

> > 
> > In the host level, vdsm should get the notification from libvirt,
> > and as
> > you suggested report it in the vm stats when polled by the engine.
> > So
> > the user can see the notification on a watchdog action taken, and
> > he can still
> > stop / restart the VM if he wishes to.
> > 
> > Does that make sense?
> 
> --
> Ryan Harper
> Software Engineer; Linux Technology Center
> IBM Corp., Austin, Tx
> ryanh at us.ibm.com
> 
>