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

["Daniel P. Berrangé" <berrange@redhat.com>]

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.

Regards,
Daniel
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