Re: [libvirt] [PATCH] storage: add RBD support to disk source pool translation
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.
Cheers,
--
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