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From:   Pingfan Liu <kernelfans@gmail.com>
Date:   Fri, 24 May 2019 11:11:13 +0800
Message-ID: <CAFgQCTuAEbST8ZdSJmPDTPbqkL3uZ8j6U-vTWT879wARDhUwTw@mail.gmail.com>
Subject: Re: [PATCHv2] kernel/crash: make parse_crashkernel()'s return value
 more indicant
To:     Matthias Brugger <mbrugger@suse.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, Rich Felker <dalias@libc.org>,
        linux-ia64@vger.kernel.org,
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Matthias, ping? Any suggestions?

Thanks,
Pingfan


On Thu, May 2, 2019 at 2:22 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>
> On Thu, Apr 25, 2019 at 4:20 PM Pingfan Liu <kernelfans@gmail.com> wrote:
> >
> > On Wed, Apr 24, 2019 at 4:31 PM Matthias Brugger <mbrugger@suse.com> wrote:
> > >
> > >
> > [...]
> > > > @@ -139,6 +141,8 @@ static int __init parse_crashkernel_simple(char *cmdline,
> > > >               pr_warn("crashkernel: unrecognized char: %c\n", *cur);
> > > >               return -EINVAL;
> > > >       }
> > > > +     if (*crash_size == 0)
> > > > +             return -EINVAL;
> > >
> > > This covers the case where I pass an argument like "crashkernel=0M" ?
> > > Can't we fix that by using kstrtoull() in memparse and check if the return value
> > > is < 0? In that case we could return without updating the retptr and we will be
> > > fine.
> After a series of work, I suddenly realized that it can not be done
> like this way. "0M" causes kstrtoull() to return -EINVAL, but this is
> caused by "M", not "0". If passing "0" to kstrtoull(), it will return
> 0 on success.
>
> > >
> > It seems that kstrtoull() treats 0M as invalid parameter, while
> > simple_strtoull() does not.
> >
> My careless going through the code. And I tested with a valid value
> "256M" using kstrtoull(), it also returned -EINVAL.
>
> So I think there is no way to distinguish 0 from a positive value
> inside this basic math function.
> Do I miss anything?
>
> Thanks and regards,
> Pingfan