Re: [PATCH/RFC 26/48] videodev2.h: Add request field to v4l2_pix_format_mplane

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Laurent,

On Fri, Dec 18, 2015 at 6:16 PM, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>> > @@ -1987,7 +1988,8 @@ struct v4l2_pix_format_mplane {
>> >
>> >     __u8                            ycbcr_enc;
>> >     __u8                            quantization;
>> >     __u8                            xfer_func;
>> >
>> > -   __u8                            reserved[7];
>> > +   __u8                            reserved[3];
>> > +   __u32                           request;
>>
>> I think I mentioned this before: I feel uncomfortable using 4 bytes of the
>> reserved fields when the request ID is limited to 16 bits anyway.
>
> I'm still unsure whether request IDs should be 16 or 32 bits long. If we go
> for 16 bits then I'll of course make this field a __u16.
>
>> I would prefer a __u16 here. Also put the request field *before* the
>> reserved array, not after.
>
> The reserved array isn't aligned to a 32 bit (or even 16 bit) boundary. I can
> put the request field before it, with a 8 bit hole before the field.

There's no alignment at all due to:

>> >  } __attribute__ ((packed));

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds