Can HyperV KVP daemon detect if running under Windows Server

Tue Mar 19 08:58:05 UTC 2013

----- Original Message -----
> > -----Original Message-----
> > From: Tomas Hozza [mailto:thozza at redhat.com]
> > Sent: Monday, March 18, 2013 11:39 AM
> > To: KY Srinivasan
> > Cc: Jason Wang
> > Subject: Re: Can HyperV KVP daemon detect if running under Windows
> > Server
> > 
> > ----- Original Message -----
> > > > -----Original Message-----
> > > > From: Tomas Hozza [mailto:thozza at redhat.com]
> > > > Sent: Monday, March 18, 2013 11:15 AM
> > > > To: KY Srinivasan
> > > > Cc: Jason Wang
> > > > Subject: Re: Can HyperV KVP daemon detect if running under
> > > > Windows
> > > > Server
> > > >
> > > > I tested the hyperv KVP daemon on RHEL-6.4 running on libvirt
> > > > KVM virtual machine. None of hv_* kmod-s was loaded. The daemon
> > > > is running just fine and netlink_send() completes successfully
> > > > even if proper drivers are not loaded.
> > > >
> > > > [root at localhost ~]# modprobe hv_vmbus
> > > > FATAL: Error inserting hv_vmbus (/lib/modules/2.6.32-
> > > > 358.el6.x86_64/kernel/drivers/hv/hv_vmbus.ko): No such device
> > > > [root at localhost ~]# modprobe hv_utils
> > > > FATAL: Error inserting hv_utils (/lib/modules/2.6.32-
> > > > 358.el6.x86_64/kernel/drivers/hv/hv_utils.ko): No such device
> > > > [root at localhost ~]# lsmod | grep hv
> > > > [root at localhost ~]# service hypervkvpd start
> > > > Starting Hyper-V KVP daemon                                [
> > > >  OK  ]
> > > > [root at localhost ~]# service hypervkvpd status
> > > > hv_kvp_daemon (pid 1509) is running...
> > > > [root at localhost ~]# grep KVP /var/log/messages
> > > > Mar 18 16:00:50 localhost KVP: KVP starting; pid is:1509
> > > > [root at localhost ~]# uname -a
> > > > Linux localhost.localdomain 2.6.32-358.el6.x86_64 #1 SMP Tue
> > > > Jan 29
> > > > 11:47:41 EST
> > > > 2013 x86_64 x86_64 x86_64 GNU/Linux
> > > >
> > > > Maybe there could be some timeout for driver registration.
> > > > After it the daemon would exit if it got no reply from
> > > > kernel driver.
> > >
> > > In that case, as you suggest maybe we can have a timeout on the
> > > first
> > > receive from the kernel. In the current code, once the daemon
> > > registers, the kernel component sends the LIS version number and
> > > this message is guaranteed to come soon after the daemon
> > > registers.
> > > If this does not happen, we can conclude that we are not on
> > > Hyper-V.
> > >
> > > >
> > > > After having a look on the kernel driver I know this can not
> > > > be done before some issues in the kernel driver are fixed.
> > > >
> > > > The problem is that the kernel driver at the moment handles
> > > > daemon registration only for the first time. On the other
> > > > hand the daemon wants to register with the driver every time
> > > > it is started. This can be real problem for example when
> > > > the daemon is restarted (stopped and started). You can read
> > > > my longer and more explanatory comment in Red Hat Bugzilla [1].
> > >
> > > Why would you want to stop/restart the daemon. Not having the
> > > daemon,
> > > can only create more problems since the kernel component holds
> > > onto
> > > the host transaction until the daemon registers. We should view
> > > the
> > > daemon as simply an extension of the kernel driver.
> > 
> > If you update the hypervkvpd package the daemon is restarted. In
> > the
> > current daemon code the registration part is written as:
> > 
> > ...
> > if ((in_hand_shake) && (op == KVP_OP_REGISTER1)) {
> >     /* handle registration */
> > }
> > ...
> > 
> > so it is possible that you update the daemon, it is restarted and
> > wants
> > to register with the driver. It sends the registration message to
> > driver.
> > The driver ignores this message since it has no transaction active
> > from
> > the Host so it is not expecting any messages from Guest. The daemon
> > ends up in a state when it is "in_hand_shake" and waiting for the
> > registration
> > to complete, BUT (because how the registration part is written) it
> > will
> > handle requests from the driver (Host). I think this is not very
> > fortunate
> > and it is kind of "design issue". User should NOT have to restart
> > (or unload
> > kernel modules and load them again) after he updated the daemon.
> 
> True; but as I said the daemon is to be viewed as simply an extension
> of the kernel component. If this is done, then you would not be
> updating the daemon independently of the kernel component. I guess
> the problem you are running into is because you are  viewing the
> daemon as an independent component that can be updated independently
> of the kernel piece. Perhaps, this is a packaging issue.
> 
> Regards,
> 
> K. Y

I see your point. It is true that we ship hyperv daemon as a separate
package. I understand the daemon is just an extension to kernel driver
and has no purpose without it.

But I don't like the way it is now anyway. Even if you look at the daemon
as just an extension to the kernel part user should not need to restart
whole Guest to get it to an "initial" state of module and the daemon.
There might be some bug in the daemon, but the driver can be just fine.
In that case I would expect that the daemon can be updated without any
problems and without restarting the system (or unloading and loading driver).

I would like to know what other people think about this. CC-ing
Haiyang Zhang and devel at linuxdriverproject.org.

Regards,

Tomas Hozza

> > 
> > Regards,
> > 
> > Tomas Hozza
> > 
> > >
> > > >
> > > > Regards,
> > > >
> > > > Tomas Hozza
> > > >
> > > > ----- Original Message -----
> > > > > Tomas,
> > > > >
> > > > > Sorry for the delayed response. The kernel driver only loads
> > > > > when
> > > > > Linux is running on Hyper-V. We could leverage this to not
> > > > > have
> > > > > the
> > > > > daemon running when not hosted on Hyper-V. The current code
> > > > > as it
> > > > > stands, the daemon  exits if the netlink_send() fails. When
> > > > > not
> > > > > running on Hyper-V, does the initial send that registers the
> > > > > daemon
> > > > > succeed.
> > > > >
> > > > > Regards,
> > > > >
> > > > > K. Y
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Tomas Hozza [mailto:thozza at redhat.com]
> > > > > > Sent: Monday, March 18, 2013 7:13 AM
> > > > > > To: Jason Wang
> > > > > > Cc: KY Srinivasan
> > > > > > Subject: Fwd: Can HyperV KVP daemon detect if running under
> > > > > > Windows
> > > > > > Server
> > > > > > Importance: High
> > > > > >
> > > > > > Hi.
> > > > > >
> > > > > > I got no response to my email I sent some time ago
> > > > > > so I'm sending it again. Maybe you just overlooked
> > > > > > it. Thank you in advance for the response.
> > > > > >
> > > > > > Regards,
> > > > > >
> > > > > > Tomas Hozza
> > > > > >
> > > > > > ----- Forwarded Message -----
> > > > > > > Hi.
> > > > > > >
> > > > > > > I'm wondering if there is any way for the hyperv kvp
> > > > > > > daemon
> > > > > > > detect if it is running as a guest on Windows Server host
> > > > > > > or
> > > > > > > not. And furthermore run only if it is a guest under
> > > > > > > Windows
> > > > > > > Server. Now hyperv kvp daemon is a default package in a
> > > > > > > Virtualization group of packages on RHEL 6.4. Some people
> > > > > > > are
> > > > > > > not happy that it is installed and running by default
> > > > > > > when
> > > > > > > the Virtualization group is selected.
> > > > > > >
> > > > > > > Do you have any suggestions? I don't know how the kernel
> > > > > > > driver
> > > > > > > is working (one that hyperv kvp daemon registers with).
> > > > > > > Would
> > > > > > > it
> > > > > > > be possible to get some useful information from it?
> > > > > > >
> > > > > > > Thank you.
> > > > > > >
> > > > > > > Regards,
> > > > > > >
> > > > > > > Tomas Hozza
> > > > > >
> > > > >
> > > > >
> > > >
> > >
> > >
> > 
> 
> 