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Re: [RFC][PATCH 1/5] Virtualization/containers: startup [message #1253 is a reply to message #1239]

Fri, 03 February 2006 17:15

Linus Torvalds
Messages: 11
Registered: February 2006

Junior Member

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

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[Message index]

		[RFC][PATCH 1/5] Virtualization/containers: startup By: Kirill Korotaev on Fri, 03 February 2006 16:57
		[RFC][PATCH 2/5] Virtualization/containers: UIDs By: dev on Fri, 03 February 2006 17:01
		[RFC][PATCH 3/5] Virtualization/containers: UTSNAME By: dev on Fri, 03 February 2006 17:04
		Re: [RFC][PATCH 3/5] Virtualization/containers: UTSNAME By: ebiederm on Mon, 06 February 2006 08:21
		Re: [RFC][PATCH 3/5] Virtualization/containers: UTSNAME By: dev on Mon, 06 February 2006 08:51
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Fri, 03 February 2006 17:22
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Linus Torvalds on Fri, 03 February 2006 17:49
		Summary: PID virtualization , Containers, Migration By: Hubertus Franke on Fri, 03 February 2006 18:36
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Rik van Riel on Fri, 03 February 2006 18:36
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Sun, 05 February 2006 14:52
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: ebiederm on Mon, 06 February 2006 08:39
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Mon, 06 February 2006 08:58
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: ebiederm on Mon, 06 February 2006 09:19
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Dave Hansen on Mon, 06 February 2006 16:37
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: ebiederm on Mon, 06 February 2006 18:37
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Mon, 06 February 2006 19:30
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Cedric Le Goater on Mon, 06 February 2006 22:40
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: ebiederm on Tue, 07 February 2006 01:57
		swsusp done by migration (was Re: [RFC][PATCH 1/5] Virtualization/containers: startup) By: Pavel Machek on Wed, 08 February 2006 21:54
		Re: swsusp done by migration (was Re: [RFC][PATCH 1/5] Virtualization/containers: startup) By: ebiederm on Thu, 09 February 2006 18:20
		Re: swsusp done by migration (was Re: [RFC][PATCH 1/5] Virtualization/containers: startup) By: Kyle Moffett on Fri, 10 February 2006 00:21
		Re: swsusp done by migration (was Re: [RFC][PATCH 1/5] Virtualization/containers: startup) By: Sam Vilain on Fri, 10 February 2006 04:31
		Re: Re: swsusp done by migration (was Re: [RFC][PATCH 1/5] Virtualization/containers: startup) By: vaverin on Fri, 10 February 2006 06:23
		Re: Re: swsusp done by migration (was Re: [RFC][PATCH 1/5] Virtualization/containers: startup) By: Sam Vilain on Sat, 11 February 2006 02:38
		Re: Re: swsusp done by migration (was Re: [RFC][PATCH 1/5] Virtualization/containers: startup) By: vaverin on Sat, 11 February 2006 17:29
		Re: swsusp done by migration (was Re: [RFC][PATCH 1/5] Virtualization/containers: startup) By: Kyle Moffett on Fri, 10 February 2006 08:29
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Nigel Cunningham on Fri, 10 February 2006 05:40
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Dave Hansen on Fri, 03 February 2006 18:34
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Jeff Garzik on Fri, 03 February 2006 18:55
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Hubertus Franke on Fri, 03 February 2006 19:18
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Hubertus Franke on Fri, 03 February 2006 19:56
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Greg KH on Fri, 03 February 2006 20:19
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Sun, 05 February 2006 15:10
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Sun, 05 February 2006 15:05
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Dave Hansen on Mon, 06 February 2006 16:35
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Mon, 06 February 2006 16:50
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Linus Torvalds on Mon, 06 February 2006 16:56
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Mon, 06 February 2006 17:19
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Sam Vilain on Tue, 07 February 2006 00:28
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Tue, 07 February 2006 12:19
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Sam Vilain on Tue, 07 February 2006 22:21
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Mon, 20 February 2006 11:54
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Linus Torvalds on Fri, 03 February 2006 17:15
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Hubertus Franke on Fri, 03 February 2006 20:34
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Sun, 05 February 2006 15:11
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Hubertus Franke on Sun, 05 February 2006 15:39
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Mon, 06 February 2006 09:06
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Cedric Le Goater on Mon, 06 February 2006 22:31
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Tue, 07 February 2006 12:25
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: Benjamin Herrenschmid on Mon, 06 February 2006 00:56
		Re: Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: dev on Mon, 06 February 2006 09:01
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: ebiederm on Mon, 06 February 2006 08:31
		Re: [RFC][PATCH 1/5] Virtualization/containers: startup By: ebiederm on Fri, 10 February 2006 06:01

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