[Devel] Re: [RFC][PATCH 1/5] Virtualization/containers: startup

[Kirill Korotaev]

Linus,

Not a problem and fully agree with you.
Just had to better review patch before sending.

Do you have any other ideas/comments on this?
I will send additional IPC/filesystems virtualization patches a bit later.

Kirill

> On Fri, 3 Feb 2006, Kirill Korotaev wrote:
>> This patch introduces some abstract container/VPS kernel structure and tiny
>> amount of operations on it.
> 
> Please don't use things like "vps_t".
> 
> It's a _mistake_ to use typedef for structures and pointers. When you see 
> a
> 
> 	vps_t a;
> 
> in the source, what does it mean?
> 
> In contrast, if it says
> 
> 	struct virtual_container *a;
> 
> you can actually tell what "a" is. 
> 
> Lots of people think that typedefs "help readability". Not so. They are 
> useful only for 
> 
>  (a) totally opaque objects (where the typedef is actively used to _hide_
>      what the object is). 
> 
>      Example: "pte_t" etc opaque objects that you can only access using 
>      the proper accessor functions.
> 
>      NOTE! Opaqueness and "accessor functions" are not good in themselves. 
>      The reason we have them for things like pte_t etc is that there 
>      really is absolutely _zero_ portably accessible information there.
> 
>  (b) Clear integer types, where the abstraction _helps_ avoid confusion 
>      whether it is "int" or "long".
> 
>      u8/u16/u32 are perfectly fine typedefs. 
> 
>      NOTE! Again - there needs to be a _reason_ for this. If something is 
>      "unsigned long", then there's no reason to do
> 
> 	typedef long myflags_t;
> 
>      but if there is a clear reason for why it under certain circumstances 
>      might be an "unsigned int" and under other configurations might be 
>      "unsigned long", then by all means go ahead and use a typedef.
> 
>  (c) when you use sparse to literally create a _new_ type for 
>      type-checking.
> 
> Maybe there are other cases too, but the rule should basically be to NEVER 
> EVER use a typedef unless you can clearly match one of those rules.
> 
> In general, a pointer, or a struct that has elements that can reasonably 
> be directly accessed should _never_ be a typedef.
> 
> 		Linus
>