Re: [RFC PATCH 5/5] v4l2-ctl: add an option to list controls in a machine-readable format

[Antonio Ospite <ao2@ao2.it>]

On Mon, 7 Jan 2019 11:18:58 +0100
Hans Verkuil <hverkuil@xs4all.nl> wrote:

> On 01/03/2019 07:01 PM, Antonio Ospite wrote:
> > Add a new option --list-ctrls-values to list the values of controls in
> > a format which can be passed again to --set-ctrl.
> > 
> > This can be useful to save and restore device settings:
> > 
> >   $ v4l2-ctl --list-ctrls-values >settings.txt 2>/dev/null
> >   $ v4l2-ctl --set-ctrl "$(cat settings.txt)"
> > 
> > The new option has been tested with the vivid driver and it works well
> > enough to be useful with a real driver as well.
> > 
> > String controls are not supported for now, as they may not be parsed
> > correctly by --set-ctrl if they contain a comma or a single quote.
> > 
> > Signed-off-by: Antonio Ospite <ao2@ao2.it>
> > ---
> >  utils/v4l2-ctl/v4l2-ctl-common.cpp | 72 ++++++++++++++++++++++++++----
> >  utils/v4l2-ctl/v4l2-ctl.1.in       |  4 ++
> >  utils/v4l2-ctl/v4l2-ctl.cpp        |  1 +
> >  utils/v4l2-ctl/v4l2-ctl.h          |  1 +
> >  4 files changed, 69 insertions(+), 9 deletions(-)
> > 
> > diff --git a/utils/v4l2-ctl/v4l2-ctl-common.cpp b/utils/v4l2-ctl/v4l2-ctl-common.cpp
> > index 7777b45c..b4124608 100644
> > --- a/utils/v4l2-ctl/v4l2-ctl-common.cpp
> > +++ b/utils/v4l2-ctl/v4l2-ctl-common.cpp
[...]
> > @@ -1102,13 +1146,23 @@ void common_get(cv4l_fd &_fd)
> >  
> >  void common_list(cv4l_fd &fd)
> >  {
> > -	if (options[OptListCtrls] || options[OptListCtrlsMenus]) {
> > -		struct print_format classic_format = {
> > -			.print_class_name = print_class_name,
> > -			.print_qctrl = print_qctrl,
> > -			.show_menus = options[OptListCtrlsMenus],
> > -		};
> > -
> > -		list_controls(fd.g_fd(), &classic_format);
> > +	if (options[OptListCtrls] || options[OptListCtrlsMenus] || options[OptListCtrlsValues]) {
> > +		if (options[OptListCtrlsValues]) {
> > +			struct print_format machine_format = {
> > +				.print_class_name = NULL,
> > +				.print_qctrl = print_qctrl_values,
> > +				.show_menus = 0,
> > +			};
> > +
> > +			list_controls(fd.g_fd(), &machine_format);
> > +		} else {
> > +			struct print_format classic_format = {
> > +				.print_class_name = print_class_name,
> > +				.print_qctrl = print_qctrl,
> > +				.show_menus = options[OptListCtrlsMenus],
> > +			};
> > +
> > +			list_controls(fd.g_fd(), &classic_format);
> > +		}
> 
> I don't like this struct print_format.
>

Hi Hans,

the idea was based on two considerations:
  1. decide the format once and for all, avoiding to check each time a
     control is printed.
  2. have at least some partial infrastructure in case some
     other export formats were to be added.

But yeah, as 2. seems quite unlikely I can go with a more essential
approach for now, no problem.

> I would prefer something like this:
> 
> Rename print_qctrl to print_qctrl_readable() and create a new print_qctrl:
> 
> static void print_qctrl(int fd, struct v4l2_query_ext_ctrl *queryctrl,
>                 struct v4l2_ext_control *ctrl, int show_menus)
> {
> 	if (options[OptListCtrlsValues])
> 		print_qctrl_values(fd, queryctrl, ctrl, show_menus);
> 	else
> 		print_qctrl_readable(fd, queryctrl, ctrl, show_menus);
> }
>

Since "readable" here means "human readable", while "values" is meant
for a "machine readable" output, I'd "avoid" the word "readable" at
all and go with "details" or "description":

	if (options[OptListCtrlsValues])
		print_qctrl_values(fd, queryctrl, ctrl, show_menus);
	else
		print_qctrl_details(fd, queryctrl, ctrl, show_menus);

> And in print_control you can just skip printing the class name if
> options[OptListCtrlsValues] is set.
>

OK.

> I would like to see string controls being supported. I would recommend
> to just write the string as a hexdump. It avoids having to escape characters.
> 
> The same can be done for compound/array controls. In fact, you could write
> all controls that way. It would simplify things a lot.
>

But then --set-ctrl would need to be extended to parse the hexdump,
wouldn't it? Do you already have a syntax in mind?

TBH, I kept things simple hoping to re-use --set-ctrl without too much
work.

> Also, when options[OptListCtrlsValues] is set you should skip all WRITE_ONLY
> controls, all BUTTON controls, and all volatile controls. They are not
> relevant if you are just interested in controls that can be set.
>

That I will do in any case, thank you.

> Regards,
> 
> 	Hans

Thank you,
   Antonio

-- 
Antonio Ospite
https://ao2.it
https://twitter.com/ao2it

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