[libvirt] [PATCH] storage: add RBD support to disk source pool translation

Thibault VINCENT thibault.vincent at arkena.com
Wed Jul 1 12:30:13 UTC 2015

On 06/25/2015 09:16 PM, John Ferlan wrote:
> My assumption without doing too much thinking is that at some point the
> virStorageBackendRBDRefreshPool will reconnect for you in the
> storageDriverAutostart path...
> While not exactly the same, consider how the iSCSI pool handles uses the
> checkPool callback.
> During storagePoolUpdateState, if the 'checkPool' callback determines
> the pool is active, then storagePoolUpdateState will call refreshPool
> with a NULL conn; otherwise, we wait for Autostart.
> So perhaps if the RBD backend had a checkPool that only did some sort of
> cursory check to ensure there was the infrastructure necessary for the
> ensuing refreshPool to work.
> Of course in the UpdateState path, 'conn == NULL', so the
> virStorageBackendRBDOpenRADOSConn won't be happy if it has authdata, but
> that's a decision you can make in your refreshPool callback... I don't
> have a conn, thus I cannot do "something".

Thanks a lot, that really helped.

Indeed the iSCSI pool do not require a conn because session state is
kept outside of libvirt, so a secret is not required by refreshPool when
called during storageStateInitialize.

While RBD backend requires the Rados connection for pretty much
anything, and has to pull a secret. Hence during storageStateInitialize
we cannot implement a checkPool or refreshPool without a conn handle.

Now I can understand why we can't have secret access until the
*Initialize loop completes, but during *Autostart it's fine. Only that
it's too late to recover domains.

Maybe we would need a new path here. We can't autostart the qemu driver
before attempting to reconnect, right, to prevent VMs running twice. But
then how could we get a callback in RBD backend to be invoked with a
valid conn before? Has this problem been addressed in an other way already?

I cannot see where the current infrastructure may allow that.
It would be nice that some drivers be considered 'essentials' and
initialized before. (Or even going dependency-based.)
How do you think this could evolve?

For now I'll dive in other drivers code to search for similar case, and
hardcode part of the init for in-house use... time constraints.


Thibault VINCENT - Lead System Engineer, Infrastructure -
Arkena | Phone: +33 1 58 68 62 38 | Mobile: +33 6 78 97 01 08
27 Blvd Hippolyte Marquès, 94200 Ivry-sur-Seine, France | www.arkena.com
Arkena - Ready to Play

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