Re: [PATCH 2/5] nfsd: Fix independence of a few nfsd related headers

[Trond Myklebust <Trond.Myklebust@netapp.com>]

On Thu, 2009-10-22 at 10:18 +0200, Boaz Harrosh wrote:
> On 10/22/2009 02:28 AM, Trond Myklebust wrote:
> > On Wed, 2009-10-21 at 10:14 +0200, Boaz Harrosh wrote:
> >> An header should be compilation independent, .i.e pull in
> >> any header who's declarations are directly used by this header.
> >> And not let users re-include all it's dependencies all over
> >> again.
> >>
> >> [At the end of the day what's the use of a header if it does
> >>  not have more then one user?]
> > 
> > 
> > The problem with this is that you quickly end up including the same
> > header files over and over and over again as they get pulled in several
> > times over by different headers.
> > 
> > 
> > 
> 
> What is the problem with that?
> 
> two things:
> 1. it is unavoidable.
> 2. That's why we invented the #ifndef FOO_H #define FOO_H for.
> 3. Look at the current mess, to the point that you don't understand why
>    the code does not compile, you end up just copy-past the include list
>    of that other file, and now actually do end with extra un-needed includes.
>    (Don't believe me look at the last patch as proof).
> 4. So I add to an header a use of a type that now needs a new include.
>    All my users do not compile any more. What to do? OK I'll include it so
>    not to change all existing users all over again. Now we get a double
>    standard. All headers used before any users, must be carried around.
>    The late comers are escaped.
> 5. The opposite of 4. An header is no longer needed. Extra header left at all
>    users.
> 
> It used to be a problem before me and you have begun programing.
> Since then the cpp looks at it's internal structures and will not re-open.
> Note that the compiler never sees the second instance, ever.
> 
> That said we have no choice of the matter. It is a Kernel style guide. I
> should know because I was banged on the head with it a couple of times.
> And rightly so.
> 
> Come on that was a joke right
> Boaz

No. What I'm saying is that this doesn't have to be an absolute rule.
The Kernel style guide assumes that everything in 'include/*' is going
to be exported all around the kernel.
The problem is that we put a lot of stuff which is private to fs/nfs and
fs/nfsd in there. Those header files do not have to absolutely follow
the style guide rule, 'cos we know what is being included before and
after them...

Cheers
  Trond

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com