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From:   Pingfan Liu <kernelfans@gmail.com>
Date:   Thu, 2 May 2019 14:22:06 +0800
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Subject: Re: [PATCHv2] kernel/crash: make parse_crashkernel()'s return value
 more indicant
To:     Matthias Brugger <mbrugger@suse.com>
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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