Re: [PATCH v3 12/20] monitor: introduce monitor_cur_hmp() function

[Markus Armbruster <armbru@redhat.com>]

Daniel P. Berrangé <berrange@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);
    }

> 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 <berrange@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.

>  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(); }