[Qemu-devel] Re: [PATCH 1/2] Print asynchronous notifications on request

[Anthony Liguori]

Amit Shah wrote:
> This patch adds the ability to selectively enable asynchronous notifications
> from individual qemu subsystems by a new 'notify' monitor command.
>
> This is helpful for programs currently parsing monitor output.
>   

I'd rather see two monitors be supported and the second monitor issue an 
explicit "listen" command to wait for async notifications

This mechanism scares me a fair bit since you're printing over the user 
prompt.

> A sample invocation will look like this:
>
> (qemu)
>     <vnc connection closed>
> (qemu) notify vnc on
>     <vnc connection closed>
> (qemu) # VNC: Closing down connection 127.0.0.1:1
>
> Notice that the output is prefixed by '#'. Also, it will appear on the
> line that has '(qemu) ' already output on it.
>
> Signed-off-by: Amit Shah <address@hidden>
> ---
>  qemu/console.h |    4 ++++
>  qemu/monitor.c |   34 ++++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+), 0 deletions(-)
>
> diff --git a/qemu/console.h b/qemu/console.h
> index 383ea1a..0cf575c 100644
> --- a/qemu/console.h
> +++ b/qemu/console.h
> @@ -292,6 +292,8 @@ void curses_display_init(DisplayState *ds, int full_screen);
>  /* x_keymap.c */
>  extern uint8_t _translate_keycode(const int key);
>
> +#define MAX_ASYNC_EVENTS  0
> +
>  /* FIXME: term_printf et al should probably go elsewhere so everything
>     does not need to include console.h  */
>  /* monitor.c */
> @@ -299,6 +301,8 @@ void monitor_init(CharDriverState *hd, int show_banner);
>  void term_puts(const char *str);
>  void term_vprintf(const char *fmt, va_list ap);
>  void term_printf(const char *fmt, ...) __attribute__ ((__format__ (__printf__, 
> 1, 2)));
> +void term_printf_async(const int event, const char *fmt, ...)
> +  __attribute__ ((__format__ (__printf__, 2, 3)));
>  void term_print_filename(const char *filename);
>  void term_flush(void);
>  void term_print_help(void);
> diff --git a/qemu/monitor.c b/qemu/monitor.c
> index 7ff9890..ef871d0 100644
> --- a/qemu/monitor.c
> +++ b/qemu/monitor.c
> @@ -65,6 +65,8 @@ typedef struct term_cmd_t {
>      const char *help;
>  } term_cmd_t;
>
> +int async_printable_events[MAX_ASYNC_EVENTS];
> +
>  #define MAX_MON 4
>  static CharDriverState *monitor_hd[MAX_MON];
>  static int hide_banner;
> @@ -122,6 +124,24 @@ void term_printf(const char *fmt, ...)
>      va_end(ap);
>  }
>
> +void term_printf_async(const int event, const char *fmt, ...)
> +{
> +    va_list ap;
> +    va_start(ap, fmt);
> +
> +    if (event > MAX_ASYNC_EVENTS)
> +        goto cleanup;
> +    if (!async_printable_events[event])
> +        goto cleanup;
> +
> +    term_printf("# ");
> +    term_vprintf(fmt, ap);
> +
> +cleanup:
> +    va_end(ap);
> +    return;
> +}
> +
>  void term_print_filename(const char *filename)
>  {
>      int i;
> @@ -210,6 +230,18 @@ static void do_help(const char *name)
>      help_cmd(name);
>  }
>
> +static void do_notify_async_events(char *event_str, char *enable)
> +{
> +    int event;
> +
> +    return;
> +
> +    if (!strcmp(enable, "on"))
> +        async_printable_events[event] = 1;
> +    else
> +        async_printable_events[event] = 0;
> +}
> +
>  static void do_commit(const char *device)
>  {
>      int i, all_devices;
> @@ -1517,6 +1549,8 @@ static const term_cmd_t term_cmds[] = {
>      { "balloon", "i", do_balloon,
>        "target", "request VM to change it's memory allocation (in MB)" },
>      { "set_link", "ss", do_set_link, "name [up|down]" },
> +    { "notify", "ss", do_notify_async_events,
> +      "NULL on|off", "enable / disable printing of notifications for the specified 
> event" },
>      { NULL, NULL, },
>  };
>
>