On Fri, Sep 19, 2025 at 02:43:41PM +0200, Markus Armbruster wrote:
> Daniel P. Berrangé <berra...@redhat.com> writes:
>
> > A number of callers use monitor_cur() followed by !monitor_cur_is_qmp().
>
> "A number of"? I can see just one:
>
> int error_vprintf(const char *fmt, va_list ap)
> {
> Monitor *cur_mon = monitor_cur();
>
> if (cur_mon && !monitor_cur_is_qmp()) {
> return monitor_vprintf(cur_mon, fmt, ap);
> }
> return vfprintf(stderr, fmt, ap);
> }
Opps, that'll be referring to the other use of monitor_cur() in my
patches that I then removed when I re-ordered the series.
>
> > This is undesirable because monitor_cur_is_qmp() will itself call
> > monitor_cur() again, and monitor_cur() must acquire locks and do
> > hash table lookups. Introducing a monitor_cur_hmp() helper will
> > combine the two operations into one reducing cost.
>
> This made me expect the patch replaces the undesirable uses. It does
> not; the new function remains unused for now.
>
> > Signed-off-by: Daniel P. Berrangé <berra...@redhat.com>
> > ---
> > include/monitor/monitor.h | 1 +
> > monitor/monitor.c | 14 ++++++++++++++
> > stubs/monitor-core.c | 5 +++++
> > tests/unit/test-util-sockets.c | 1 +
> > 4 files changed, 21 insertions(+)
> >
> > diff --git a/include/monitor/monitor.h b/include/monitor/monitor.h
> > index 296690e1f1..c3b79b960a 100644
> > --- a/include/monitor/monitor.h
> > +++ b/include/monitor/monitor.h
> > @@ -14,6 +14,7 @@ typedef struct MonitorOptions MonitorOptions;
> > extern QemuOptsList qemu_mon_opts;
> >
> > Monitor *monitor_cur(void);
> > +Monitor *monitor_cur_hmp(void);
> > Monitor *monitor_set_cur(Coroutine *co, Monitor *mon);
> > bool monitor_cur_is_qmp(void);
> >
> > diff --git a/monitor/monitor.c b/monitor/monitor.c
> > index e1e5dbfcbe..cff502c53e 100644
> > --- a/monitor/monitor.c
> > +++ b/monitor/monitor.c
> > @@ -84,6 +84,20 @@ Monitor *monitor_cur(void)
> > return mon;
> > }
> >
> > +Monitor *monitor_cur_hmp(void)
> > +{
> > + Monitor *mon;
> > +
> > + qemu_mutex_lock(&monitor_lock);
> > + mon = g_hash_table_lookup(coroutine_mon, qemu_coroutine_self());
> > + if (mon && monitor_is_qmp(mon)) {
> > + mon = NULL;
> > + }
> > + qemu_mutex_unlock(&monitor_lock);
> > +
> > + return mon;
> > +}
> > +
> > /**
> > * Sets a new current monitor and returns the old one.
> > *
> > diff --git a/stubs/monitor-core.c b/stubs/monitor-core.c
> > index b498a0f1af..1e0b11ec29 100644
> > --- a/stubs/monitor-core.c
> > +++ b/stubs/monitor-core.c
> > @@ -7,6 +7,11 @@ Monitor *monitor_cur(void)
> > return NULL;
> > }
> >
> > +Monitor *monitor_cur_hmp(void)
> > +{
> > + return NULL;
> > +}
> > +
> > bool monitor_cur_is_qmp(void)
> > {
> > return false;
> > diff --git a/tests/unit/test-util-sockets.c b/tests/unit/test-util-sockets.c
> > index bd48731ea2..d40813c682 100644
> > --- a/tests/unit/test-util-sockets.c
> > +++ b/tests/unit/test-util-sockets.c
> > @@ -72,6 +72,7 @@ int monitor_get_fd(Monitor *mon, const char *fdname,
> > Error **errp)
> > * otherwise we get duplicate syms at link time.
> > */
> > Monitor *monitor_cur(void) { return cur_mon; }
> > +Monitor *monitor_cur_hmp(void) { return cur_mon; }
>
> @cur_mon is a fake here. Why do you make this fake monitor HMP? If we
> somehow call error_vprintf(), it'll call monitor_vprintf(), which will
> dereference the fake monitor. Best possible outcome would be an
> immediate crash.
Current code has 'monitor_cur' return 'cur_mon', and 'monitor_cur_is_qmp'
(below) return 'false'. IOW, the current behaviour of the stubs is that
'cur_mon' is HMP, so I just maintained those semantics.
We've stubbed monitor_vprintf() too so it'll abort() no matter what, as
we don't expect that code path to be triggered from this test suite.
> > bool monitor_cur_is_qmp(void) { return false; }
> > Monitor *monitor_set_cur(Coroutine *co, Monitor *mon) { abort(); }
> > int monitor_vprintf(Monitor *mon, const char *fmt, va_list ap) { abort(); }
With regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
