Re: CTLTYPE_UINT?

[Alan Barrett <apb%cequrux.com@localhost>]

On Sat, 04 Oct 2014, Justin Cormack wrote:
> I agree about being explicit with the 32 bitness, but using S64 
> and U64 as the 64 bit names to be consistent with FreeBSD might 
> make sense.

The S64 and U64 names are fine.  I'd also add S32 and U32.

> long types seems best avoided if possible, you can see the 
> temptation to use them for memory amounts, but you could be 
> running on 32 bit userspace on a 64 bit kernel.

One of the reasons that I like user/kernel interfaces to use 
types with explicit bit width is to simplify running 32-bit 
userland on 64-bit kernels.  If you use a type whose actual size 
changes between 32 bits and 64 bits, then the kernel has to have 
a compatibility layer to copy and adjust the data, and tools like 
kdump or ktruss should also translate (it's a bug that they don't 
do so today).  If you use a type that's always 64 bits, then it's 
much easier to deal with.  Occasionally, an argument for run-time 
efficiency in a 32-bit userland will outweigh this argument for 
ease of coding, and then a type whose size changes should be 
used.

--apb (Alan Barrett)