linux-kernel - Re: [PATCH v2 1/5] media: visl: Fix params permissions/defaults mismatch

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Date:   Thu, 23 Nov 2023 09:41:09 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Detlev Casanova <detlev.casanova@...labora.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-media@...r.kernel.org,
        Daniel Almeida <daniel.almeida@...labora.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Subject: Re: [PATCH v2 1/5] media: visl: Fix params permissions/defaults
 mismatch

On 22/11/2023 17:38, Detlev Casanova wrote:
> On Wednesday, November 22, 2023 10:56:20 A.M. EST Hans Verkuil wrote:
>> On 24/10/2023 21:09, Detlev Casanova wrote:
>>> `false` was used as the keep_bitstream_buffers parameter permissions.
>>> This looks more like a default value for the parameter, so change it to
>>> 0 to avoid confusion.
>>>
>>> Reviewed-by: Daniel Almeida <daniel.almeida@...labora.com>
>>> Signed-off-by: Detlev Casanova <detlev.casanova@...labora.com>
>>> ---
>>>
>>>  drivers/media/test-drivers/visl/visl-core.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/media/test-drivers/visl/visl-core.c
>>> b/drivers/media/test-drivers/visl/visl-core.c index
>>> 9970dc739ca5..df6515530fbf 100644
>>> --- a/drivers/media/test-drivers/visl/visl-core.c
>>> +++ b/drivers/media/test-drivers/visl/visl-core.c
>>> @@ -74,7 +74,7 @@ MODULE_PARM_DESC(visl_dprintk_nframes,
>>>
>>>  		 " the number of frames to trace with dprintk");
>>>  
>>>  bool keep_bitstream_buffers;
>>>
>>> -module_param(keep_bitstream_buffers, bool, false);
>>> +module_param(keep_bitstream_buffers, bool, 0);
>>
>> ???
>>
>> This last parameter is the permission, it makes no sense that this
>> is either 0 or false: then nobody can see it in /sys/modules/.
> 
> It makes sense if we want it set when the module is loaded only. This way, we 
> don't have to manage the parameters values changing while work is being done 
> and keep it simple.
> It could be made readable if that looks better, but there is no real need for 
> it to be read either.

Why not? It makes it easy to read what this module option's value is.

I now see that both visl and vidtv uses 0 a lot, so I'm OK with this
patch for consistency.

But I think especially these test-drivers should use 0444 instead of 0
so you can see how the test driver is configured. That might actually
be relevant when writing tests using these drivers.

Perhaps separate patches for visl and vidtv that change 0 to 0444 for all
the module parameters?

Regards,

	Hans

> 
>> Typically this is 0444 if it is readable only, or 0644 if it can be
>> written by root.
>>
>> Regards,
>>
>> 	Hans
>>
>>>  MODULE_PARM_DESC(keep_bitstream_buffers,
>>>  
>>>  		 " keep bitstream buffers in debugfs after streaming is 
> stopped");
>