On Tue, Nov 22, 2011 at 04:53:33PM -0500, Andrew Cathrow wrote:
> 
> 
> ----- Original Message -----
> > From: "Adam Litke" <a...@us.ibm.com>
> > To: vdsm-devel@lists.fedorahosted.org
> > Sent: Tuesday, November 22, 2011 4:29:41 PM
> > Subject: MOM integration questions
> > 
> > Hi guys,
> > 
> > I've got MOM up and running as a vdsm thread but I've hit two small
> > problems.
> > I'll bounce them around on the list to see if people have some ideas.
> > 
> > 1.) Libvirt SASL authentication
> > 
> > I was able to easily modify MOM to connect to libvirt by hardcoding
> > the vdsm
> > credentials.  Obviously this is not an acceptable long-term solution.
> >  What is
> > the best way to share the vdsm libvirt password with MOM in a way
> > that does not
> > compromise security?  Whatever method we choose should not involve
> > vdsm-specific
> > changes to MOM.  For starters I think I will just place the username
> > and
> > password in the mom.conf file.  We could make this file readable only
> > by the
> > vdsm user.  Thoughts?
> 
> Is it safe just to read it from /etc/pki/vdsm/keys/libvirt_password 
> 
> What's the reason for not wanting VDSM specific changes in MOM, is this 
> project is part of oVirt then we can always assume VDSM is present.

My initial integration strategy for MOM is to alter it such that vdsm can
load the MOM logic as a python module and execute it in a new vdsmd thread.  I
believe the cleanest interface is possible when the interaction between MOM and
vdsm is one way (ie. vdsm controls MOM).  In this scenario, MOM would provide
all of the APIs that vdsm needs to have the required level of control but MOM
would not call back into VDSM.  By doing this, MOM can remain focused on its
specific role in the stack without being aware of idiosyncrasies in vdsm.  There
are two exceptions to this rule: Collectors and Controllers.  VDSM can be a data
source.  In this case, we can write a vdsm Collector that knows how to query
VDSM for host and guest statistics.  VDSM can also be a 'tuning mechanism'
against which we can write a Controller to execute certain privileged
operations.  What I am concerned about is the need to update supervdsm with a
new command each time we want to tweak a new sysfs file.

> > 
> > 2.) Permissions
> > 
> > The first error I noticed was MOM failing to adjust KSM via sysfs:
> > 
> > 2011-11-22 10:13:48,313 - mom.Controllers.KSM - WARNING - KSM: Failed
> > to write
> > /sys/kernel/mm/ksm/run: Permission denied
> > 
> > MOM is used to running as root so that it can adjust these settings.
> >  I would
> > prefer not to complicate the MOM architecture by having a separate
> > process that
> > receives instructions from the main MOM thread and then applies the
> > requested
> > changes as root.
> > 
> > Another solution would be to allow MOM to run as a completely
> > separate daemon
> > (as it has been originally doing).  In this scenario, vdsm would
> > reconfigure MOM
> > by replacing the default configuration file and policy.  vdsm could
> > then
> > interact with the running momd via the existing xmlrpc interface.
> > 
> > Thoughts on these issues?

-- 
Adam Litke <a...@us.ibm.com>
IBM Linux Technology Center

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