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

[Akihiko Odaki <akihiko.odaki@daynix.com>]

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.