Parsing dbus introspect

* Parsing dbus introspect
@ 2019-10-18  2:34 Patrick Venture
  2019-10-18  2:46 ` William Kennington
  0 siblings, 1 reply; 6+ messages in thread
From: Patrick Venture @ 2019-10-18  2:34 UTC (permalink / raw)
  To: James Feist; +Cc: Peter Lundgren, OpenBMC Maillist

With dbus-sensors, if I follow the Association property, i can find
the board that owns the sensor.  However, we have a use-case where we
want sensors to be able to have their own EntityId and EntityInstance
values configured via the json --

This lead to three situations:
1) sensor's board doesn't implement the Ipmi decoration
2) sensor's board implements the Ipmi decoration
3) sensor's board implements the Ipmi decoration, but the sensor has
override values in the sensor dbus object owned by EntityManager.

The way I see to do it is to introspect on the dbus path and service,
and then search the list of interfaces to find one that starts
"xyz.openbmc_project.Configuration" and then search that interface for
an "EntityId" and "EntityInstance" property, and if present, read
them.

So this leads me to this email:
1) Has anyone already got an XML parser they like and has used it in
this way?  Just to save me from figuring out the exact way to wire it
up.

busctl call xyz.openbmc_project.EntityManager
/xyz/openbmc_project/inventory/system/board/18_razorback_card/18_rzbk_temp
org.freedesktop.DBus.Introspectable Introspect

s "<!DOCTYPE node PUBLIC \"-//freedesktop//DTD D-BUS Object
Introspection 1.0//EN\"\n\"http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd\">\n<node>\n
<interface name=\"org.freedesktop.DBus.Peer\">\n  <method
name=\"Ping\"/>\n  <method name=\"GetMachineId\">\n   <arg type=\"s\"
name=\"machine_uuid\" direction=\"out\"/>\n  </method>\n
</interface>\n <interface
name=\"org.freedesktop.DBus.Introspectable\">\n  <method
name=\"Introspect\">\n   <arg name=\"data\" type=\"s\"
direction=\"out\"/>\n  </method>\n </interface>\n <interface
name=\"org.freedesktop.DBus.Properties\">\n  <method name=\"Get\">\n
<arg name=\"interface\" direction=\"in\" type=\"s\"/>\n   <arg
name=\"property\" direction=\"in\" type=\"s\"/>\n   <arg
name=\"value\" direction=\"out\" type=\"v\"/>\n  </method>\n  <method
name=\"GetAll\">\n   <arg name=\"interface\" direction=\"in\"
type=\"s\"/>\n   <arg name=\"properties\" direction=\"out\"
type=\"a{sv}\"/>\n  </method>\n  <method name=\"Set\">\n   <arg
name=\"interface\" direction=\"in\" type=\"s\"/>\n   <arg
name=\"property\" direction=\"in\" type=\"s\"/>\n   <arg
name=\"value\" direction=\"in\" type=\"v\"/>\n  </method>\n  <signal
name=\"PropertiesChanged\">\n   <arg type=\"s\" name=\"interface\"/>\n
  <arg type=\"a{sv}\" name=\"changed_properties\"/>\n   <arg
type=\"as\" name=\"invalidated_properties\"/>\n  </signal>\n
</interface>\n <interface
name=\"xyz.openbmc_project.Configuration.TMP421\">\n  <property
name=\"Address\" type=\"t\" access=\"read\">\n  </property>\n
<property name=\"Bus\" type=\"t\" access=\"read\">\n  </property>\n
<property name=\"Name\" type=\"s\" access=\"read\">\n  </property>\n
<property name=\"Type\" type=\"s\" access=\"read\">\n  </property>\n
</interface>\n</node>\n"

It's pretty easy -- it takes no parameters and returns a string that I
feed into an XML parser, and then walk the nodes --> but has anyone
already done this? Maybe I can use their code as a snippet or if it's
in a common OpenBMC library?

If nobody else has done this yet, I'll reply to this email with the
patch that does it :)  I'm definitely interested in suggestions on a
favored c++ XML parser.

Thanks
Patrick

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