On Thu, Oct 31, 2013 at 12:46:07PM -0600, Eric Blake wrote:
On 10/31/2013 12:34 PM, Daniel P. Berrange wrote:
>
> IIUC, this is still going to be introducing a direct code path dependancy
> between the QEMU and storage driver code though.
No, src/qemu would still get backing chain details via src/util, the way
it has always done. Only src/util has to have the magic to call into
src/storage backends (if the right backend is present, chase the backing
chain of the network disk; if absent, forcefully assume raw as is
already currently done).
>
> Currently src/qemu depends only on code in src/util & src/conf[1]. For
> the storage pool bits, it can call indirectly via src/libvirt.c APIs, but
> it does not call anything in src/storage/ directly. I really want this
> to remain that way, because avoiding direct calls is key to enabling
> us to split libvirtd up into separate daemons per driver in the future.
>
> Daniel
>
> [1] Yes, there's a dep on src/network too, which i was never at all happy
> about, and which needs to be refactored / removed in some manner in
> the future
This is a useful discussion, because I don't want to be developing code
that violates layering constraints. So, am I on the right track by
allowing src/util to call into src/storage backends, or is the only
proper way to do that to have src/util call in to src/libvirt.c APIs
which then call into src/storage indirectly?
src/util shouldn't have any compile time dependancy on src/storage,
or indeed any other directory.
You could conceivably do it indirectly, by having src/storage
register some kind of plugin with src/util at startup. That way
it is only a runtime dep.
How does this compare to src/qemu/qemu_process.c, using
conn->secretDriver->secretGetValue(,
VIR_SECRET_GET_VALUE_INTERNAL_CALL), as a means of calling into
src/secret indirectly but without going through src/libvirt.c API?
Again, that's a runtime only dep. So if the libvirt_driver_secret.la
was not installed, it would not be fatal - the API calls would just
get a runtime error.
Daniel
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