Re: [PATCH v2] ui: Print available display backends with '-display help'

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 1/6/20 10:33 AM, Thomas Huth wrote:
> We already print availabled devices with "-device help", or available
> backends with "-netdev help" or "-chardev help". Let's provide a way
> for the users to query the available display backends, too.
> 
> Signed-off-by: Thomas Huth <huth@tuxfamily.org>
> ---
>   v2: Now it should work with modules, too
> 
>   include/ui/console.h |  1 +
>   ui/console.c         | 15 +++++++++++++++
>   vl.c                 |  5 +++++
>   3 files changed, 21 insertions(+)
> 
> diff --git a/include/ui/console.h b/include/ui/console.h
> index f981696848..b7e1a8e6c0 100644
> --- a/include/ui/console.h
> +++ b/include/ui/console.h
> @@ -440,6 +440,7 @@ void qemu_display_register(QemuDisplay *ui);
>   bool qemu_display_find_default(DisplayOptions *opts);
>   void qemu_display_early_init(DisplayOptions *opts);
>   void qemu_display_init(DisplayState *ds, DisplayOptions *opts);
> +void qemu_display_help(void);
>   
>   /* vnc.c */
>   void vnc_display_init(const char *id, Error **errp);
> diff --git a/ui/console.c b/ui/console.c
> index 82d1ddac9c..9556b5d8dd 100644
> --- a/ui/console.c
> +++ b/ui/console.c
> @@ -2330,6 +2330,21 @@ void qemu_display_init(DisplayState *ds, DisplayOptions *opts)
>       dpys[opts->type]->init(ds, opts);
>   }
>   
> +void qemu_display_help(void)
> +{
> +    int idx;
> +
> +    printf("Available display backend types:\n");
> +    for (idx = DISPLAY_TYPE_NONE; idx < DISPLAY_TYPE__MAX; idx++) {
> +        if (!dpys[idx]) {
> +            ui_module_load_one(DisplayType_str(idx));
> +        }
> +        if (dpys[idx]) {
> +            printf("%s\n",  DisplayType_str(dpys[idx]->type));
> +        }
> +    }
> +}
> +
>   void qemu_chr_parse_vc(QemuOpts *opts, ChardevBackend *backend, Error **errp)
>   {
>       int val;
> diff --git a/vl.c b/vl.c
> index 86474a55c9..ee15055ba2 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1869,6 +1869,11 @@ static void parse_display(const char *p)
>   {
>       const char *opts;
>   
> +    if (is_help_option(p)) {
> +        qemu_display_help();
> +        exit(0);
> +    }
> +
>       if (strstart(p, "sdl", &opts)) {
>           /*
>            * sdl DisplayType needs hand-crafted parser instead of
> 

Consider updating the manpage too:

-- >8 --
diff --git a/qemu-options.hx b/qemu-options.hx
index e9d6231438..d86ec0332a 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1585,8 +1585,9 @@ DEF("display", HAS_ARG, QEMU_OPTION_display,
  STEXI
  @item -display @var{type}
  @findex -display
-Select type of display to use. This option is a replacement for the
-old style -sdl/-curses/... options. Valid values for @var{type} are
+Select type of display to use. Use @code{-display help} to list
+available displays. This option is a replacement for the old style
+-sdl/-curses/... options. Valid values for @var{type} are
  @table @option
  @item sdl
  Display video output via SDL (usually in a separate graphics
---

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>