Re: [RFC] [PATCH] v4l2: use unsigned rather than enums in ioctl() structs

["Rémi Denis-Courmont" <remi@remlab.net>]

On Thu, 12 Apr 2012 11:55:12 -0300, Mauro Carvalho Chehab

<mchehab@redhat.com> wrote:

> I can see only two viable fixes for it:

> 

> 1) add a typedef for the enum, using the sizeof(enum) in order to select

> the

> size of the used integer.

> 

> Pros:

> 	- Patch is easy to write/easy to review;

> 	- Won't change the struct size, so applications compiled without

> 	  strong gcc optimization won't break;

> Cons:

> 	- It will add a typedef, with is ugly;

> 	- struct size on 32 bits will be different thant he size on 64 bits

> 	  (not really an issue, as v4l2-compat32 will handle that;



On which platforms do enums occupy 64-bits? Alpha? More to the point, on

which platform is enum not the same size as unsigned?



At least on x86-64, enum is 32-bits and so is unsigned.



> 	- v4l2-compat32 code may require changes.

> 

> 2) just replace it by a 32 bits integer.

> 

> Pros:

> 	- no typedefs;

> 	- struct size won't change between 32/64 bits (except when they also

> 	  have pointers);

> Cons:

> 	- will break ABI. So, a compat code is required;

> 	- will require a "videodev2.h" fork for the legacy API with the enum's;

> 	- will require a compat code to convert from enum into integer and

> 	  vice-versa.

> 

> Comments/Votes?



-- 

Rémi Denis-Courmont

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