Application that runs EventsDispatcher can safely use also cache , which
greatly improve performance. This is because cache then is properly
updated/invalidated when needed.
Instead of modifying each application to explicitly enable cache based
on this simple rule, make it implicit when EventsDispatcher is created.
Do not enable caching when EventsDispatcher is created only temporarily
in wait_for_domain_shutdown.
QubesOS/qubes-issues#3293
Power state changes are signaled with events too, so it is possible to
cache it and update/invalidate cache with events.
Additionally, admin.vm.List returns a power state, so the cache can be
populated early. This in particular greatly improves qvm-ls performance -
eliminate admin.vm.CurrentState call at all.
QubesOS/qubes-issues#3293
Reduce Admin API calls by caching returned values. The cache is not
enabled by default, because it could result in stale values being
returned. It can be enabled by setting 'cache_enabled' to True on
Qubes() object. This is safe in two cases:
- the application don't care about changed values - like a short-lived
process that retrieve values once (for example qvm-ls)
- the application listen for events and invalidate cache when property
is changed
For the second case, invalidating the cache on appropriate event
(property-set:*, property-reset:*) is done before calling other event
handlers. This is because the event may try to access the property value
(not necessary from the event arguments), so we need to be sure it will
see the new value.
FixesQubesOS/qubes-issues#5415
Retry connection on any OSError, instead of only few selected error
types. For example PermissionError may happen too (when socket is
created, but before it gets appropriate mode), which wasn't listed.
Since now event listener reports proper QubesDaemonCommunicationError
exception instead of some form of IOError. Include it for automatic
reconnect logic.
Fixes a481490 "app: fix error reporting when connection to qubesd fails"
Port 5a39e777089d8bde6d0a620830a898c1cf3dd924 ("events: add support for
wildcard event handlers") from qubes-core-admin:
Support registering handlers for more flexible wildcard events: not only
'*', but also 'something*'. This allows to register handlers for
'property-set:*' and such.
This is especially the case for domain-shutdown event for DispVM - when
handled, DispVM can be already removed. Give the handled VM object even
if actual VM is already removed. For this, avoid VM existence check by
using domains.get_blind() method.
And actually implement domains.get_blind() method - it was present only
in generic collection, but not VMCollection.
It may happen that when client handle the event, domain no longer
exists. This is for example common for DispVMs, which get removed just
after shutdown.
This will cause some events to be dropped, but one can enable blind
mode, to get them anyway (because it will not cause KeyError, even if
domain is already removed).
QubesOS/qubes-issues#3100
qubesd may be restarted during different stages of connection - either
while attempting to connect, or while already listening on events.
Adjust exception list accordingly.
This is especially important for qvm-start-gui - otherwise it crashes on
qubesd restart.
Empty parameter value is encoded as b'parameter\0\0', so we can't simply
read the data until b'\0\0', because it isn't necessary event end.
Instead, read event parts separately, according to specification.
