Re: [systemd-devel] sd-bus dynamic property table
On Mo, 13.05.19 08:25, Stephen Hemminger (step...@networkplumber.org) wrote:
> I have a simple application that does provides property table for network
> devices (maybe it would be useful for a more complete example somewhere).
> The app is more to show how to use sdbus, not to replace network manager.
>
> The next step is to add ethtool statistics. Each type of network device will
> have
> different set of named properties. How could this be implemented?
> So far, the only idea would be to dynamically build a vtable then
> register it?
>
>
> # busctl tree org.networkplumber.net1
> └─/org
> └─/org/networkplumber
> └─/org/networkplumber/net1
> └─/org/networkplumber/net1/interface
> ├─/org/networkplumber/net1/interface/eno1
> ├─/org/networkplumber/net1/interface/eno2
> ├─/org/networkplumber/net1/interface/ens11
> └─/org/networkplumber/net1/interface/lo
>
> # busctl introspect org.networkplumber.net1
> /org/networkplumber/net1/interface/eno1
> NAMETYPE SIGNATURE RESULT/VALUE FLAGS
> org.freedesktop.DBus.Introspectable interface - --
> .Introspect method- s-
> org.freedesktop.DBus.Peer interface - --
> .GetMachineId method- s-
> .Ping method- --
> org.freedesktop.DBus.Properties interface - --
> .Getmethodssv-
> .GetAll methods a{sv}-
> .Setmethodssv --
> .PropertiesChanged signalsa{sv}as --
> org.networkplumber.net1.Interface interface - --
> .carrierproperty q 1-
> .ifindexproperty q 2-
> .iflink property q 2-
> .mtuproperty q 1500 -
Simon already replied to this, but let's add some further points:
dbus' object model is modelled after the object model of common
object-oriented programming languages, i.e. Java, C# and
suchlike. They generally have immutable interface definitions,
i.e. the vtables consisting of methods and properties never change,
but the implementation of them might, and objects might expose
different interfaces at the same time, in different combinations.
It's not unlike C in many ways: a C struct definition doesn't change
either, regardless what you apply it to.
Hence: you have multiple options to model what you are trying to do:
try to split things up into multiple interfaces so that you object can
implement them in varying combinations. Or simply define all
properties at all times, but define a special value (i.e. UINT64_MAX
for a uint64_t property or so) that indicates they don't actually
apply to the current object.
Lennart
--
Lennart Poettering, Berlin
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Re: [systemd-devel] sd-bus dynamic property table
On Mon, 13 May 2019 at 08:25:03 -0700, Stephen Hemminger wrote:
> The next step is to add ethtool statistics. Each type of network device will
> have
> different set of named properties.
This is really a D-Bus API design query, not a systemd query.
The standard D-Bus Properties interface is not designed for use
with arbitrary/dynamic named attributes. It's intended to be a D-Bus
equivalent of GObject properties or Qt properties, which are set up
in the object's source code: their values might vary at runtime, but
the list of properties that exists in a class or interface is part of
the API of that class or interface and does not change[1]. Similarly,
D-Bus properties exist in an interface alongside methods and signals,
and an interface either has a Foo property or it doesn't: if it does,
then every object that implements the interface also has a Foo property.
If you need named attributes that vary between objects, I'd suggest
representing them as either a single large property with an a{sv}
as its value, or a D-Bus interface that structurally resembles
Properties but is not Properties (for instance you could call it
com.example.NetworkStatistics, replacing com.example with your reversed
domain name, and have a GetStatistics() -> a{sv} method and optionally
a StatisticsChanged signal).
The org.freedesktop.DBus.Debug.Stats interface in dbus-daemon (it's
compile-time conditional, so your dbus-daemon might not have it)
provides an example of an interface that puts arbitrary attributes
in the result of a method call.
smcv
[1] except for maybe backward-compatible feature enhancements where
newer versions introduce more properties
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[systemd-devel] sd-bus dynamic property table
I have a simple application that does provides property table for network
devices (maybe it would be useful for a more complete example somewhere).
The app is more to show how to use sdbus, not to replace network manager.
The next step is to add ethtool statistics. Each type of network device will
have
different set of named properties. How could this be implemented?
So far, the only idea would be to dynamically build a vtable then
register it?
# busctl tree org.networkplumber.net1
└─/org
└─/org/networkplumber
└─/org/networkplumber/net1
└─/org/networkplumber/net1/interface
├─/org/networkplumber/net1/interface/eno1
├─/org/networkplumber/net1/interface/eno2
├─/org/networkplumber/net1/interface/ens11
└─/org/networkplumber/net1/interface/lo
# busctl introspect org.networkplumber.net1
/org/networkplumber/net1/interface/eno1
NAMETYPE SIGNATURE RESULT/VALUE FLAGS
org.freedesktop.DBus.Introspectable interface - --
.Introspect method- s-
org.freedesktop.DBus.Peer interface - --
.GetMachineId method- s-
.Ping method- --
org.freedesktop.DBus.Properties interface - --
.Getmethodssv-
.GetAll methods a{sv}-
.Setmethodssv --
.PropertiesChanged signalsa{sv}as --
org.networkplumber.net1.Interface interface - --
.carrierproperty q 1-
.ifindexproperty q 2-
.iflink property q 2-
.mtuproperty q 1500 -
Want to be able to add these:
# ethtool -S eno1 | grep -v ' 0$'
NIC statistics:
rx_packets: 84980
tx_packets: 32068
rx_bytes: 107413644
tx_bytes: 9299204
rx_broadcast: 219
tx_broadcast: 84
rx_multicast: 152
tx_multicast: 157
multicast: 152
tx_tcp_seg_good: 1561
rx_long_byte_count: 107413644
tx_queue_0_packets: 6888
tx_queue_0_bytes: 3127349
tx_queue_1_packets: 6307
tx_queue_1_bytes: 3623152
tx_queue_2_packets: 12569
tx_queue_2_bytes: 1239345
tx_queue_3_packets: 6304
tx_queue_3_bytes: 1163512
rx_queue_0_packets: 17936
rx_queue_0_bytes: 21464312
rx_queue_1_packets: 20651
rx_queue_1_bytes: 27029893
rx_queue_2_packets: 12642
rx_queue_2_bytes: 13132543
rx_queue_3_packets: 33751
rx_queue_3_bytes: 45446976
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