Re: [Qemu-devel] [RFC 0/3] virtiofsd: get/set log level via DBus

[Stefan Hajnoczi]

On Thu, Sep 05, 2019 at 04:21:33PM +0100, Stefan Hajnoczi wrote:
> It is likely that virtiofsd will need to support "management commands" for
> reconfiguring it at runtime.  The first use case was proposed by Eryu Guan for
> getting/setting the current log level.
> 
> I promised to try out DBus as the management interface because it has a rich
> feature set and is accessible from most programming languages.  It should be
> able to support all the use cases we come up with.
> 
> This patch series is a prototype that implements the get-log-level and
> set-log-level management commands via DBus.  Use the new virtiofsctl tool to
> talk to a running virtiofsd process:
> 
>   # dbus-run-session ./virtiofsd ...
>   ...
>   Using dbus address 
> unix:abstract=/tmp/dbus-H9WBbpjk3O,guid=0be16acefb868e6025a8737f5d7124d2
>   # export 
> DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-H9WBbpjk3O,guid=0be16acefb868e6025a8737f5d7124d2
>   # ./virtiofsctl set-log-level err
> 
> Most of the work is done by gdbus-codegen(1).  It generates code for the
> org.qemu.Virtiofsd.xml interface definition.  Our code can use the simple
> virtiofsd_get/set_log_level() APIs and it will make corresponding DBus calls.
> 
> I'm pretty happy with this approach because the code is straightforward.  It
> hasn't even triggered seccomp failures yet :).
> 
> Error handling is a little problematic.  I noticed that virtiofsctl silently
> returns success even if it cannot talk to virtiofsd.  This is due to the code
> generated by gdbus-codegen(1) which has no error reporting :(.  This can be
> solved by writing more low-level GDBus code instead of using the high-level
> generated bindings.
> 
> What do you think about this approach?

Hi Eryu Guan,
Have you had a chance to try these patches?  Do they meet your
requirements for being able to get/set the log level at runtime?

Stefan

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