On Mon, 2018-04-09 at 13:45 +0100, Daniel P. Berrangé wrote: > On Mon, Apr 09, 2018 at 02:25:04PM +0200, Pavel Hrdina wrote: > > On Mon, Apr 09, 2018 at 01:47:32PM +0200, Katerina Koukiou wrote: > > > Signed-off-by: Katerina Koukiou <kkoukiou@xxxxxxxxxx> > > > --- > > > data/org.libvirt.Connect.xml | 4 ++++ > > > src/connect.c | 20 ++++++++++++++++++++ > > > test/test_connect.py | 1 + > > > 3 files changed, 25 insertions(+) > > > > Adding Dan to CC because I'm not that familiar with D-Bus > > conventions. > > This API can be exported as property, however it returns rather > > large > > string and not a simple value so I'm not sure whether method would > > be > > better in this case. > > The concept of properties is essentially a convenience to make live > easier > for mapping into language bindings / higher level object systems. > > At the protocol level, the properties are handling via a standard > interface > with a handful of methods > > https://dbus.freedesktop.org/doc/dbus-specification.html#standard-int > erfaces-properties > > So whether you have a "Capabilities" property, or a "GetCapabilities" > method, you'll still have a method call on the wire protocol, with > the > full string transmitted. There is also a signal that servers should > emit when a property value changes so that clients know that if they > have cached the property value, they should refetch it. > > So potential issues are > > - If we don't emit PropertyChange signals, clients may cache out > of date capabilities > - If clients pre-fetch properties there'll be a small perf hit > - If we have lots of properties, then the overall size of all > properties combined might cause problems for GetAll > > The first item is the one that would concern me in this instance. > The libvirt capabilities data can change between calls, and libvirt > has no way to notify you of such changes. Thus IMHO it is better > exposed as a dynamic method call than a property. Leave properties > for libvirt things that are esentially static data, unless we're > able to provide PropertyChange signals. > Thanks for the detailed explanation. I will adjust it and repost. > > > Regards, > Daniel Regards, Katerina -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
