Parsing dbus introspect

[Patrick Venture]

On Thu, Oct 17, 2019 at 10:55 PM Lei YU <mine260309 at gmail.com> wrote:
>
> I think object mapper already does this for you.
> Just call GetSubtree and you get a list of objects and the interfaces
> they implement.
>
> E.g.
>  busctl call "xyz.openbmc_project.ObjectMapper"
> "/xyz/openbmc_project/object_mapper"
> "xyz.openbmc_project.ObjectMapper" GetSubTree sias
> /xyz/openbmc_project/inventory/system/board/18_razorback_card/18_rzbk_temp
> 0 0

Thanks!  Although GetSubTree returned nothing, I checked the other methods:

busctl call xyz.openbmc_project.ObjectMapper
/xyz/openbmc_project/object_mapper xyz.openbmc_project.ObjectMapper
GetObject sas /xyz/openbmc_project/inventory/system/board/18_razorback_card/18_rzbk_temp
0

a{sas} 1 "xyz.openbmc_project.EntityManager" 1
"xyz.openbmc_project.Configuration.TMP421"

I didn't know the last parameter was optional -- so I have always used
it for a slightly different purpose.  This is excellent, thanks!

>
> On Fri, Oct 18, 2019 at 11:33 AM Patrick Venture <venture at google.com> wrote:
> >
> > On Thu, Oct 17, 2019 at 8:29 PM Patrick Venture <venture at google.com> wrote:
> > >
> > > On Thu, Oct 17, 2019 at 7:46 PM William Kennington <wak at google.com> wrote:
> > > >
> > > > Looks like systemd doesn't even use an xml parser
> > > > https://github.com/systemd/systemd/blob/cee97d57687e93e07a8ee36edf0e0d0f3317fccc/src/busctl/busctl-introspect.c
> > >
> > > I'm thinking I'll just regex for what I seek in this case.  Since I
> > > know the lead of the string, and how the surrounding bits should
> > > appear.  I just need the interface name, a good regex use-case. :)
> >
> > <interface name=\"xyz.openbmc_project.Configuration.TMP421\">
> >
> > >
> > > >
> > > > On Thu, Oct 17, 2019 at 7:35 PM Patrick Venture <venture at google.com> wrote:
> > > > >
> > > > > 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