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authorDavid Herrmann <dh.herrmann@gmail.com>2015-07-31 13:25:04 +0200
committerDavid Herrmann <dh.herrmann@gmail.com>2015-07-31 13:56:39 +0200
commit11f254be0c27b1944a1df8e7c14d83e56ebe7d9b (patch)
tree2b455dbdaff4fa2e558e5f0be49d47abf36e4f52 /src/quotacheck
parent3407fcd575b31416ae1658572590d0b4973f5ace (diff)
bus-proxy: make StartServiceByName synchronous
The StartServiceByName() call was provided by dbus-daemon to activate a service without sending a message. On receiption, dbus-daemon schedules an activation request (different modes are supported) and sends back the reply once activation is done. With kdbus, we marked StartServiceByName() as deprecated. There is no real reason to start services explicitly. Instead, applications should just *use* the service and rely on it being activated implicitly. However, we provide compatibility with dbus-daemon and implement StartServiceByName() on the proxy via a call to org.freedesktop.DBus.Peer.Ping() on the destination. This will activate the peer implicitly as part of the no-op Ping() method call (regardless whether the peer actually implements that call). Now, the problem is, StartServiceByName() was synchronous on dbus-daemon but isn't on bus-proxy. Hence, on return, there is no guarantee that ListNames includes the activated name. As this is required by some applications, we need to make this synchronous. This patch makes the proxy track the Ping() method call and send the reply of StartServiceByName() only once Ping() returned. We do not look at possible errors of Ping(), as there is no strict requirement for the peer to implement org.freedesktop.DBus.Peer. Furthermore, any interesting error should have already been caught by sd_bus_send() before. Note: This race was triggered by gdbus. The gdbus-proxy implementation relies on a name to be available after StartServiceByName() returns. This is highly fragile and should be dropped by gdbus. Even if the call is synchronous, there is no reason whatsoever to assume the service did not exit-on-idle before ListNames() returns. However, this race is much less likely than the startup race, so we try to be compatible to dbus-daemon now.
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