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

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Message-Id: <20080115111018.1e27a229.randy.dunlap@oracle.com>
Date:	Tue, 15 Jan 2008 11:10:18 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	"Anton Salikhmetov" <salikhmetov@...il.com>
Cc:	"Christoph Hellwig" <hch@...radead.org>, 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()

On Tue, 15 Jan 2008 22:02:54 +0300 Anton Salikhmetov wrote:

> 2008/1/15, Christoph Hellwig <hch@...radead.org>:
> > On Tue, Jan 15, 2008 at 07:02:44PM +0300, Anton Salikhmetov wrote:

> > > @@ -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.

CodingStyle does not try to cover Everything.  Nor do we want it to.

At any rate, there is a desire for functions to have a single point
of return, regardless of the amount of cleanup to be done, so I agree
with Christoph's comments.


> 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.


---
~Randy
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