linux-kernel - Re: [PATCH v3 1/3] selftests/mm/write_to_hugetlbfs: parse -s as size

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Message-ID: <20251223084035.67ba1b76@pumpkin>
Date: Tue, 23 Dec 2025 08:40:35 +0000
From: David Laight <david.laight.linux@...il.com>
To: Li Wang <liwang@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, David Hildenbrand <david@...nel.org>, Mark Brown
 <broonie@...nel.org>, Shuah Khan <shuah@...nel.org>, Waiman Long
 <longman@...hat.com>
Subject: Re: [PATCH v3 1/3] selftests/mm/write_to_hugetlbfs: parse -s as
 size_t

On Tue, 23 Dec 2025 10:41:22 +0800
Li Wang <liwang@...hat.com> wrote:

> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > > > It is best to use strtoul() and check the 'end' character is '\0'.  
> > >
> > > Hmm, that sounds like we need to go back to the patch V1 [1] method.
> > > But I am not sure, @Andrew Morton, do you think so?
> > >
> > > --- a/tools/testing/selftests/mm/write_to_hugetlbfs.c
> > > +++ b/tools/testing/selftests/mm/write_to_hugetlbfs.c
> > > @@ -86,10 +86,17 @@ int main(int argc, char **argv)
> > >         while ((c = getopt(argc, argv, "s:p:m:owlrn")) != -1) {
> > >                 switch (c) {
> > >                 case 's':
> > > -                       if (sscanf(optarg, "%zu", &size) != 1) {
> > > -                               perror("Invalid -s.");
> > > +                       char *end = NULL;

Initialiser not needed.

> > > +                       unsigned long tmp = strtoul(optarg, &end, 10);
> > > +                       if (errno || end == optarg || *end != '\0') {

I doubt that use of errno is correct.
Library functions that set errno on error don't set it to zero.
The only test needed there is *end != '\'.
(end == optarg will be picked up by size == 0 later - if that is actually
needed to stop things breaking.)

> > > +                               perror("Invalid -s size");
> > >                                 exit_usage();
> > >                         }
> > > +                       if (tmp == 0) {

No point checking for zero before the assigning the 'unsigned long' to 'size_t'.
So the result of strtoul() can just be just assigned to 'size'.
(Ignoring the fact that size_t will be unsigned long.)

> > > +                               perror("size not found");
> > > +                               exit_usage();
> > > +                       }
> > > +                       size = (size_t)tmp;
> > >                         break;
> > >                 case 'p':  
> >
> > Geeze guys, it's just a selftest.
> >
> > hp2:/usr/src/linux-6.19-rc1> grep -r scanf tools/testing/selftests | wc -l
> > 177
> >
> > if your command line breaks the selftest, fix your command line?  
> 
> Yes, I am ok with sscanf() :-).

What was wrong with atoi() ?
Or, at most, strtoul() with a check that *end == 0.

	David

> 
> In fact, write_to hugetlbfs currently only accepts arguments from
> charge_reserved_hugetlb.sh, and the way the '-s' is used is not
> very diverse.
> 
> --
> Regards,
> Li Wang
>