linux-kernel - Re: [PATCH v5 1/2] mm: add kstrimdup function

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Message-Id: <20140130135111.cffc7d8852dd38545bddeb75@linux-foundation.org>
Date:	Thu, 30 Jan 2014 13:51:11 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Sebastian Capella <sebastian.capella@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-pm@...r.kernel.org, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, "Joe Perches" <joe@...ches.com>,
	"Mikulas Patocka" <mpatocka@...hat.com>,
	"Michel Lespinasse" <walken@...gle.com>,
	"Shaohua Li" <shli@...nel.org>,
	"Jerome Marchand" <jmarchan@...hat.com>,
	"Joonsoo Kim" <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v5 1/2] mm: add kstrimdup function

On Thu, 30 Jan 2014 13:45:45 -0800 Sebastian Capella <sebastian.capella@...aro.org> wrote:

> Quoting Andrew Morton (2014-01-30 13:22:51)
> > On Thu, 30 Jan 2014 13:11:57 -0800 Sebastian Capella <sebastian.capella@...aro.org> wrote:
> > > +char *kstrimdup(const char *s, gfp_t gfp)
> > > +{
> > > +     char *buf;
> > > +     char *begin = skip_spaces(s);
> > > +     size_t len = strlen(begin);
> > > +
> > > +     while (len > 1 && isspace(begin[len - 1]))
> > > +             len--;
> > 
> > That's off-by-one isn't it?  kstrimdup("   ") should return "", not " ".
> > 
> > > +     buf = kmalloc_track_caller(len + 1, gfp);
> > > +     if (!buf)
> > > +             return NULL;
> > > +
> > > +     memcpy(buf, begin, len);
> > > +     buf[len] = '\0';
> > > +
> > > +     return buf;
> > > +}
> 
> Hi Andrew,
> 
> I think this is a little tricky.
> 
> For an empty string, the function relies on skip_spaces to point begin
> at the \0'.
> 
> Alternately, if we don't have an empty string, we know we have at least 1
> non-space, non-null character at begin[0], and there's no need to check it,
> so the loop stops at [1].  If there's a space at 1, we just put the '\0'
> there.
> 
> We could check at [0], but I think its already been checked by skip_spaces.

heh, OK, tricky.
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