Re: [PATCH] vl: Print display options for -display help

[Akihiko Odaki]

On 2023/12/15 22:07, BALATON Zoltan wrote:
> On Fri, 15 Dec 2023, Daniel P. Berrangé wrote:
> > On Fri, Dec 15, 2023 at 01:43:37PM +0100, BALATON Zoltan wrote:
> > > On Fri, 15 Dec 2023, Akihiko Odaki wrote:
> > > > On 2023/12/14 22:00, BALATON Zoltan wrote:
> > > > > > So we go from:
> > > > > >
> > > > > > $ ./qemu-system-aarch64 -display help
> > > > > > Available display backend types:
> > > > > > none
> > > > > > gtk
> > > > > > sdl
> > > > > > curses
> > > > > > cocoa
> > > > > > dbus
> > > > > >
> > > > > > to:
> > > > > >
> > > > > > $ ./qemu-system-aarch64 -display help
> > > > > > -display 
> > > > > > sdl[,gl=on|core|es|off][,grab-mod=<mod>][,show-cursor=on|off]
> > > > > >            [,window-close=on|off]
> > > > > > -display gtk[,full-screen=on|off][,gl=on|off][,grab-on-hover=on|off]
> > > > > >            
> > > > > > [,show-tabs=on|off][,show-cursor=on|off][,window-close=on|off]
> > > > > >            [,show-menubar=on|off]
> > > > > > -display vnc=<display>[,<optargs>]
> > > > > > -display curses[,charset=<encoding>]
> > > > > > -display cocoa[,full-grab=on|off][,swap-opt-cmd=on|off]
> > > > > > -display dbus[,addr=<dbusaddr>]
> > > > > >             [,gl=on|core|es|off][,rendernode=<file>]
> > > > > > -display cocoa[,show-cursor=on|off][,left-command-key=on|off]
> > > > > > -display none
> > > > > >                select display backend type
> > > > > >                The default display is equivalent to
> > > > > >                "-display gtk"
> > > > > >
> > > > > > The latter is indeed more helpful.
> > > > >
> > > > > It is more helpful but maybe a bit overwhelming. Would it be
> > > > > possible to only print the options with -display cocoa,help similar
> > > > > to how -device help lists devices and -device sm501,help lists
> > > > > options for one device? Adding info about default to -display help
> > > > > is really helpful though (that could also be marked with (default)
> > > > > like in -machine help.
> > > >
> > > > It's copied from what qemu-system-aarch64 -h outputs. At least it's 
> > > > less
> > > > overwhelming than qemu-system-aarch64 -h.
> > >
> > > This changes what -display help does so if some script depends on 
> > > that it
> > > may not be a good idea. Since the same info is already in -help maybe 
> > > this
> > > change to add that to -display help as well is not the best solution 
> > > so I'd
> > > say drop this patch and leave it as it is for now.
> >
> > We consider help output to be only for humans.
> >
> > No scripts should ever be parsing any QEMU output, as we provide
> > QMP for automated detection/querying of features.
> >
> > IOW, if some script is parsing help output we are fine to break
> > them if it improves QEMU's output for humans in a justiable way.
>
> OK fair enough. I'd still like some more consitency with -cpu help and 
> -machine help and -device help which all list avalable options and then 
> can take help for further help for individual items where applicable. So 
> it would be better if -display and -audio could behave the same. (Are 
> there any other options that might be missing this?)
>
> Out of curiousicy what's the way to query available display backends for 
> programs by QMP then?

There is no method available as far as I know. All of these quirks are 
caused by the design of the display infrastructure not integrated well 
with QOM.