linux-kernel - Re: [PATCH 1/2] Massive code cleanup of sys

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Date:	Tue, 15 Jan 2008 22:02:54 +0300
From:	"Anton Salikhmetov" <salikhmetov@...il.com>
To:	"Christoph Hellwig" <hch@...radead.org>
Cc:	linux-mm@...ck.org, jakob@...hought.net,
	linux-kernel@...r.kernel.org, valdis.kletnieks@...edu,
	riel@...hat.com, ksm@...dk, staubach@...hat.com,
	jesper.juhl@...il.com, torvalds@...ux-foundation.org,
	a.p.zijlstra@...llo.nl, akpm@...ux-foundation.org,
	protasnb@...il.com, miklos@...redi.hu
Subject: Re: [PATCH 1/2] Massive code cleanup of sys_msync()

2008/1/15, Christoph Hellwig <hch@...radead.org>:
> On Tue, Jan 15, 2008 at 07:02:44PM +0300, Anton Salikhmetov wrote:
> > +++ b/mm/msync.c
> > @@ -1,24 +1,25 @@
> >  /*
> >   *   linux/mm/msync.c
> >   *
> > + * The msync() system call.
> >   * Copyright (C) 1994-1999  Linus Torvalds
> > + *
> > + * Massive code cleanup.
> > + * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@...il.com>
>
> Please don't put the changelog in here, that's what the log in the SCM
> is for.  And while you're at it remove the confusing file name comment.
> This should now look something like:
>
> /*
>  * The msync() system call.
>  *
>  * Copyright (C) 1994-1999  Linus Torvalds
>  * Copyright (C) 2008 Anton Salikhmetov <salikhmetov@...il.com>
>  */

Thanks!

I'll take into account your recommendation.

>
> > @@ -33,71 +34,65 @@ asmlinkage long sys_msync(unsigned long start, size_t len, int flags)
> >       unsigned long end;
> >       struct mm_struct *mm = current->mm;
> >       struct vm_area_struct *vma;
> > -     int unmapped_error = 0;
> > -     int error = -EINVAL;
> > +     int error = 0, unmapped_error = 0;
> >
> >       if (flags & ~(MS_ASYNC | MS_INVALIDATE | MS_SYNC))
> > -             goto out;
> > +             return -EINVAL;
> >       if (start & ~PAGE_MASK)
> > -             goto out;
> > +             return -EINVAL;
>
> The goto out for a simple return style is used quite commonly in kernel
> code to have a single return statement which makes code maintaince, e.g.
> adding locks or allocations simpler.  Not sure that getting rid of it
> makes a lot of sense.

Sorry, I can't agree. That's what is written in the CodingStyle document:

The goto statement comes in handy when a function exits from multiple
locations and some common work such as cleanup has to be done.

The second part of requirement does not hold true for the sys_msync() routine.

>
> > +             file = vma->vm_file;
> > +             if ((flags & MS_SYNC) && file && (vma->vm_flags & VM_SHARED)) {
>
> Given that file is assigned just above it would be more readable to test
> it first.

The second part of my solution changes this code, anyway.

>
> > +                     if (error)
> > +                             return error;
>
> This should be an goto out, returns out of the middle of the function
> make reading and maintaining the code not so nice.

Sorry, I don't think so. No "common cleanup" is needed here.

>
> >       return error ? : unmapped_error;
>
> Care to get rid of this odd GNU extension while you're at it and use
> the proper

I do also think that this GNU extension is not readable,
so I'll take your recommentation into account.

>
>         return error ? error : unmapped_error;
>
> ?
>
>
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