Re: [libvirt] [PATCH 0/7] Prepare for daemon split
On Thu, Apr 05, 2018 at 01:06:28PM -0400, Laine Stump wrote:
On 03/28/2018 11:18 AM, Daniel P. Berrangé wrote:
> When we split up the daemons, libvirtd will need to forward different
> sets of APIs to different daemons. This means libvirtd is going to need
> to have multiple virConnectPtr instances open.
Have you done any thinking about what will need to be added to the
network driver API (or how)? I'd like to be involved with that.
I've not thought about it beyond hoping magic ponies will solve the
problems you describe below :) So far I'm just working on the general
refactoring to let us (optionally) create the various daemons so there
is something concrete to explore the problems with.
One part that troubles me is that there will no longer be a
parent-child
relationship between the process keeping track of network allocations
and the qemu process - currently if a qemu process dies, libvirtd knows
about it and can recover the resources that had been allocated, but with
the network driver in a separate process, qemu could die and
libvirtd-qemu might not be around to notify libvirtd-network (or
whatever we end up calling the processes).
BTW, naming will be virt${DRIVER}d (eg virtqemud, virtnetworkd, etc) but
minor detail. Anyway, if QEMU dies, and virtqemud isn't running, then
when virtqemud starts up again it would notice that the QEMU went away
and do recovery, presumably telling other daemons to release resources
if needed.
Likewise, there is the nwfilter driver's complicated callback
setup to
reload the iptables rules of all relevant domains when a filter's
definition is changed. I haven't thought about the details, but I think
that will need some "interesting" handling.
I was thinking the nwfilter automatic rebuild ought to be possible to
have entirely self-contained, because rebuilding shouldn't need help
from the QEMU driver - it just needs the TAP dev to exist.
Also the network driver and nwfilter driver both use virfirewall.c,
which has a mutex to prevent simultaneous updates; either we'll need to
put that functionality into one of the drivers and have the other one
call it via a public API, or we'll need to rely on iptables -w (but even
that could lead to different results, since it's locking just during
application of a single rule rather than a complete transaction (as
defined by virfirewall.c).
Two possible options
- Replace the mutex with a lock file + fcntl() locks, that both
virnetworkd & virnwfilterd will use
- Have virnetworkd actually call virnwfilterd to setup the rules
it needs. I'm not sure if nwfilter can express the rules we
need though.
Regards,
Daniel
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