Re: [Virtio-fs] [Qemu-devel] [RFC 2/3] virtiofsd: add DBus server to handle log level changes

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Daniel P. Berrangé (berrange@redhat.com) wrote:
> On Fri, Sep 06, 2019 at 11:23:28AM +0100, Stefan Hajnoczi wrote:
> > On Thu, Sep 05, 2019 at 06:27:32PM +0100, Dr. David Alan Gilbert wrote:
> > > * Stefan Hajnoczi (stefanha@redhat.com) wrote:
> > > > Introduce a DBus server thread that runs alongside the other virtiofsd
> > > > threads.  It processes changes to the /org/qemu/virtiofsd object which
> > > > can be accessed at the org.qemu.virtiofsd location on the bus.
> > > > 
> > > > This code does not use locking because we are the only writer to the
> > > > int current_log_level variable.  More advanced management commands would
> > > > require locking to prevent race conditions with the other threads.
> > > > 
> > > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > > 
> > > OK, that is less complex than I'd feared.
> > > I guess there's something probably nice to do with name/integer mapping
> > > for warning levels that we could use from one of the libraries.
> > 
> > I used a free-form string because it's what systemd's LogLevel property
> > also does.  But I can investigate the cleanest approach for limiting it
> > to a set of string constants.
> 
> There's no concept of "enums" at the DBus protocol level. Sending enums
> in string form is the normal practice - avoiding integer values means
> you are not vulnerable to enum values changing if someone inserts a new
> constant in the middlle of the enum. This same reason is why QAPI uses
> strings for enums instead of ints.

Oh, I wasn't talking aobut changing protocol; I just meant there was
probably a neater way of doing the string look up than the opencoded way
it was done.

Dave

> Regards,
> Daniel
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Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK