[libvirt PATCH 2/3] conf: introduce support for Fibre Channel VMID

[Daniel P. Berrangé]

On Wed, Aug 04, 2021 at 11:54:07AM +0200, Pavel Hrdina wrote:
> On Wed, Aug 04, 2021 at 10:32:00AM +0100, Daniel P. Berrangé wrote:
> > On Wed, Aug 04, 2021 at 11:19:35AM +0200, Pavel Hrdina wrote:
> > > On Wed, Aug 04, 2021 at 10:09:30AM +0100, Daniel P. Berrangé wrote:
> > > > On Tue, Aug 03, 2021 at 04:29:32PM +0200, Pavel Hrdina wrote:
> > > > > Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
> > > > > ---
> > > > >  docs/formatdomain.rst               | 13 +++++++++++++
> > > > >  docs/schemas/domaincommon.rng       | 11 +++++++++++
> > > > >  src/conf/domain_conf.c              |  5 +++++
> > > > >  src/conf/domain_conf.h              |  2 ++
> > > > >  src/conf/domain_validate.c          | 19 +++++++++++++++++++
> > > > >  tests/genericxml2xmlindata/vmid.xml | 19 +++++++++++++++++++
> > > > >  tests/genericxml2xmltest.c          |  2 ++
> > > > >  7 files changed, 71 insertions(+)
> > > > >  create mode 100644 tests/genericxml2xmlindata/vmid.xml
> > > > 
> > > > > diff --git a/tests/genericxml2xmlindata/vmid.xml b/tests/genericxml2xmlindata/vmid.xml
> > > > > new file mode 100644
> > > > > index 0000000000..df984df3f5
> > > > > --- /dev/null
> > > > > +++ b/tests/genericxml2xmlindata/vmid.xml
> > > > > @@ -0,0 +1,19 @@
> > > > > +<domain type='qemu'>
> > > > > +  <name>QEMUGuest1</name>
> > > > > +  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
> > > > > +  <memory unit='KiB'>219100</memory>
> > > > > +  <currentMemory unit='KiB'>219100</currentMemory>
> > > > > +  <vcpu placement='static'>4</vcpu>
> > > > > +  <os>
> > > > > +    <type arch='x86_64' machine='q35'>hvm</type>
> > > > > +    <boot dev='hd'/>
> > > > > +  </os>
> > > > > +  <clock offset='utc'/>
> > > > > +  <vmid>someapp:c7a5fdbd-edaf-9455-926a-d65c16db1809</vmid>
> > > > 
> > > > I'm not convinced by adding this element here with this name.
> > > > 
> > > > It is rather too generic and doesn't really give any suggestion
> > > > as to what it is used for.
> > > 
> > > I was struggling with that as well. To be honest I don't know where to
> > > put it. In downstream BZ there was suggestion to place it under
> > > <blkiotune> but this is not tunning any IO so I don't thing it should
> > > belong there. We can move it closer to UUID and GENID and all this ID
> > > elements. Any idea is welcome :).
> > 
> > I'm struggling to find info on what this attribute actally does in
> > practice, and/or what format it is required to be in.
> > 
> > I was wondering what would happen if we simply wrote the VM UUID
> > into this attribute unconditionally, and thus avoid need for an
> > XML element ?
> 
> Right, should have provided some links probably, always forget to do
> that. We need to have it in XML as users will provide their own VMID
> and it can be anything, ti doesn't have to be VM UUID but it can be
> part of it. I was not able to find any specification, only some mentions
> from HW vendors:
> 
> [1] "Virtual-machine awareness: The MDS 9148T provides visibility into
>      all virtual machines that are accessing the storage LUNs in the fabric.
>      This feature is available through HBAs capable of priority tagging the
>      Virtual Machine Identifier (VMID) on every Fibre Channel frame.
>      Virtual-machine awareness can be extended to intelligent fabric services
>      such as analytics1 to visualize performance of every flow originating
>      from each virtual machine in the fabric."
> 
> [2] "Provides visibility into each virtual machine logged into the
>      fabric through HBAs capable of priority tagging the Virtual Machine
>       Identifier (VMID) on every FC frame."

IIUC, the implication is that the VMID associated with QEMU gets
associated with I/O issued from any <disk> devices that happen to
be backed by the fibre channel HBA consuming it.

> Fibre Channel VMID is can be included in every FC frame which allows
> monitoring or QoS and other things based on the VMID provided by users.
> The VMID can contain anything so a group of VMs can share the same VMID,
> for example "database". Or to allow per application and VM tracking
> another example is "database:$UUID".

Ok, so the "group of VMs can share the VMID" eliminates the option
of unconditionally using the VM UUID.


I'm inclined to suggest that we put it inside the <resource> element,
since it is essentially a tunable for FC resource control.

eg something like

  <resource>
    <fibrechannel appid="...."/>
  </resouce>

Regards,
Daniel
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