[PATCH] media: uvcvideo: drop useless assignment in uvc_parse_format()

[PATCH] media: uvcvideo: drop useless assignment in uvc_parse_format()

[Sergey Shtylyov]

Close to the end of uvc_parse_format(), the parameter buflen is decremented
(again) but that statement seems pointless as buflen isn't used afterwards.
Drop the useless assignment (gcc doesn't generate any code for it anyways).

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

Signed-off-by: Sergey Shtylyov <s.shtylyov@auroraos.dev>
---
 drivers/media/usb/uvc/uvc_driver.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index e289cc71ba98..0e78e8bcd320 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -520,7 +520,6 @@ static int uvc_parse_format(struct uvc_device *dev,
 		format->xfer_func = uvc_xfer_func(buffer[4]);
 		format->ycbcr_enc = uvc_ycbcr_enc(buffer[5]);
 
-		buflen -= buffer[0];
 		buffer += buffer[0];
 	} else {
 		format->colorspace = V4L2_COLORSPACE_SRGB;
-- 
2.55.0

Re: [PATCH] media: uvcvideo: drop useless assignment in uvc_parse_format()

[Sergey Shtylyov]

On 8/20/26 11:11 PM, Sergey Shtylyov wrote:

> Close to the end of uvc_parse_format(), the parameter buflen is decremented
> (again) but that statement seems pointless as buflen isn't used afterwards.
> Drop the useless assignment (gcc doesn't generate any code for it anyways).
> 
> Found by Linux Verification Center (linuxtesting.org) with the Svace static
> analysis tool.
> 
> Signed-off-by: Sergey Shtylyov <s.shtylyov@auroraos.dev>
    Duh, forgot to add that the patch is against the next branch of the
linuxtv.org/media.git repo!

[...]

MBR, Sergey

Re: [PATCH] media: uvcvideo: drop useless assignment in uvc_parse_format()

[Ricardo Ribalda]

Hi Sergey

On Thu, 20 Aug 2026 at 22:12, Sergey Shtylyov <s.shtylyov@auroraos.dev> wrote:
>
> Close to the end of uvc_parse_format(), the parameter buflen is decremented
> (again) but that statement seems pointless as buflen isn't used afterwards.
> Drop the useless assignment (gcc doesn't generate any code for it anyways).

The patch is correct, although I do not see a great benefit in
removing it. As you say, the compiler will remove it anyway. If we
modify the function to add logging or continue parsing the left over
buffer, it is going to come back to haunt us....

I leave it to Laurent or HansG to decide if they want to merge it.

Thanks!


>
> Found by Linux Verification Center (linuxtesting.org) with the Svace static
> analysis tool.
>
> Signed-off-by: Sergey Shtylyov <s.shtylyov@auroraos.dev>
> ---
>  drivers/media/usb/uvc/uvc_driver.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index e289cc71ba98..0e78e8bcd320 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -520,7 +520,6 @@ static int uvc_parse_format(struct uvc_device *dev,
>                 format->xfer_func = uvc_xfer_func(buffer[4]);
>                 format->ycbcr_enc = uvc_ycbcr_enc(buffer[5]);
>
> -               buflen -= buffer[0];
>                 buffer += buffer[0];
>         } else {
>                 format->colorspace = V4L2_COLORSPACE_SRGB;
> --
> 2.55.0
>


--
Ricardo Ribalda

Re: [PATCH] media: uvcvideo: drop useless assignment in uvc_parse_format()

[Laurent Pinchart]

On Thu, Aug 27, 2026 at 11:24:33AM +0200, Ricardo Ribalda wrote:
> Hi Sergey
> 
> On Thu, 20 Aug 2026 at 22:12, Sergey Shtylyov <s.shtylyov@auroraos.dev> wrote:
> >
> > Close to the end of uvc_parse_format(), the parameter buflen is decremented
> > (again) but that statement seems pointless as buflen isn't used afterwards.
> > Drop the useless assignment (gcc doesn't generate any code for it anyways).
> 
> The patch is correct, although I do not see a great benefit in
> removing it. As you say, the compiler will remove it anyway. If we
> modify the function to add logging or continue parsing the left over
> buffer, it is going to come back to haunt us....
> 
> I leave it to Laurent or HansG to decide if they want to merge it.

I'd rather keep the buflen update in place for the reasons explained by
Ricardo.

/me wishes for std::span<> in C

> > Found by Linux Verification Center (linuxtesting.org) with the Svace static
> > analysis tool.
> >
> > Signed-off-by: Sergey Shtylyov <s.shtylyov@auroraos.dev>
> > ---
> >  drivers/media/usb/uvc/uvc_driver.c | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > index e289cc71ba98..0e78e8bcd320 100644
> > --- a/drivers/media/usb/uvc/uvc_driver.c
> > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > @@ -520,7 +520,6 @@ static int uvc_parse_format(struct uvc_device *dev,
> >                 format->xfer_func = uvc_xfer_func(buffer[4]);
> >                 format->ycbcr_enc = uvc_ycbcr_enc(buffer[5]);
> >
> > -               buflen -= buffer[0];
> >                 buffer += buffer[0];
> >         } else {
> >                 format->colorspace = V4L2_COLORSPACE_SRGB;

-- 
Regards,

Laurent Pinchart

Re: [PATCH] media: uvcvideo: drop useless assignment in uvc_parse_format()

[Hans de Goede]

Hi,

On 28-Sep-26 22:29, Laurent Pinchart wrote:
> On Thu, Aug 27, 2026 at 11:24:33AM +0200, Ricardo Ribalda wrote:
>> Hi Sergey
>>
>> On Thu, 20 Aug 2026 at 22:12, Sergey Shtylyov <s.shtylyov@auroraos.dev> wrote:
>>>
>>> Close to the end of uvc_parse_format(), the parameter buflen is decremented
>>> (again) but that statement seems pointless as buflen isn't used afterwards.
>>> Drop the useless assignment (gcc doesn't generate any code for it anyways).
>>
>> The patch is correct, although I do not see a great benefit in
>> removing it. As you say, the compiler will remove it anyway. If we
>> modify the function to add logging or continue parsing the left over
>> buffer, it is going to come back to haunt us....
>>
>> I leave it to Laurent or HansG to decide if they want to merge it.
> 
> I'd rather keep the buflen update in place for the reasons explained by
> Ricardo.
> 
> /me wishes for std::span<> in C

Ack, I've dropped this patch from patchwork.

Regards,

Hans


> 
>>> Found by Linux Verification Center (linuxtesting.org) with the Svace static
>>> analysis tool.
>>>
>>> Signed-off-by: Sergey Shtylyov <s.shtylyov@auroraos.dev>
>>> ---
>>>  drivers/media/usb/uvc/uvc_driver.c | 1 -
>>>  1 file changed, 1 deletion(-)
>>>
>>> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
>>> index e289cc71ba98..0e78e8bcd320 100644
>>> --- a/drivers/media/usb/uvc/uvc_driver.c
>>> +++ b/drivers/media/usb/uvc/uvc_driver.c
>>> @@ -520,7 +520,6 @@ static int uvc_parse_format(struct uvc_device *dev,
>>>                 format->xfer_func = uvc_xfer_func(buffer[4]);
>>>                 format->ycbcr_enc = uvc_ycbcr_enc(buffer[5]);
>>>
>>> -               buflen -= buffer[0];
>>>                 buffer += buffer[0];
>>>         } else {
>>>                 format->colorspace = V4L2_COLORSPACE_SRGB;
> 

Re: [PATCH] media: uvcvideo: drop useless assignment in uvc_parse_format()

[Sergey Shtylyov]

On 9/29/26 12:16 PM, Hans de Goede wrote:

[...]

>>>> Close to the end of uvc_parse_format(), the parameter buflen is decremented
>>>> (again) but that statement seems pointless as buflen isn't used afterwards.
>>>> Drop the useless assignment (gcc doesn't generate any code for it anyways).
>>>
>>> The patch is correct, although I do not see a great benefit in
>>> removing it. As you say, the compiler will remove it anyway. If we
>>> modify the function to add logging or continue parsing the left over
>>> buffer, it is going to come back to haunt us....
>>>
>>> I leave it to Laurent or HansG to decide if they want to merge it.
>>
>> I'd rather keep the buflen update in place for the reasons explained by
>> Ricardo.
>>
>> /me wishes for std::span<> in C
> 
> Ack, I've dropped this patch from patchwork.

   OK, but why "Not Applicable" and not "Rejected"? :-)

> Regards,
> 
> Hans
[...]

MBR, Sergey