Re: [Qemu-devel] [PATCH v4] log: Make glib logging go through QEMU

[Stefan Hajnoczi]

On Thu, Jan 03, 2019 at 03:14:55PM +0100, Christophe Fergeau wrote:
> Hey,
> 
> On Thu, Jan 03, 2019 at 10:54:25AM +0000, Stefan Hajnoczi wrote:
> > On Fri, Dec 14, 2018 at 11:56:42AM +0100, Christophe Fergeau wrote:
> > > +static void qemu_log_func(const gchar *log_domain,
> > > +                          GLogLevelFlags log_level,
> > > +                          const gchar *message,
> > > +                          gpointer user_data)
> > > +{
> > > +    switch (log_level & G_LOG_LEVEL_MASK) {
> > > +    case G_LOG_LEVEL_DEBUG:
> > > +        /* Use same G_MESSAGES_DEBUG logic as glib to enable/disable 
> > > debug
> > > +         * messages
> > > +         */
> > > +        if (qemu_glog_domains == NULL) {
> > > +            break;
> > > +        }
> > > +        if (strcmp(qemu_glog_domains, "all") != 0 &&
> > > +          (log_domain == NULL || !strstr(qemu_glog_domains, 
> > > log_domain))) {
> > > +            break;
> > > +        }
> > > +        /* Fall through */
> > > +    case G_LOG_LEVEL_INFO:
> > > +        /* Fall through */
> > > +    case G_LOG_LEVEL_MESSAGE:
> > > +        info_report("%s: %s", log_domain, message);
> > 
> > QEMU itself uses glib, so what happens if *_report() emit more log
> > messages?  Can this result in an infinite loop?
> 
> If *_report try to output messages through the g_log API, glib will
> catch it and will abort, so not an infinite loop, but not a
> desirable outcome either.
> 
> Some low-level logging functions which are going to dump the message
> without glib (or using g_log_default_handler()) are needed.
> The timestamping/prepending of 'error:', 'warning:' to the error message
> is done right below *_report (in vreport) so this looked like a good
> place for that.

If you're confident that QEMU will never (indirectly) emit a glib log
message from the *_report() code path, then I'm happy.

Stefan

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