linux-kernel - Re: [PATCH] namespace: Replace simple_strtoul with kstrtoul to parse boot params

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Message-Id: <E07BDF4C-F76A-4050-A4B9-3D2A362A3ABE@linux.dev>
Date: Mon, 15 Dec 2025 15:17:14 +0100
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Jan Kara <jack@...e.cz>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>,
 linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] namespace: Replace simple_strtoul with kstrtoul to parse
 boot params

On 15. Dec 2025, at 10:15, Jan Kara wrote:
> On Sun 14-12-25 16:31:42, Thorsten Blum wrote:
>> Replace simple_strtoul() with the recommended kstrtoul() for parsing the
>> 'mhash_entries=' and 'mphash_entries=' boot parameters.
>> 
>> Check the return value of kstrtoul() and reject invalid values. This
>> adds error handling while preserving behavior for existing values, and
>> removes use of the deprecated simple_strtoul() helper.
>> 
>> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
> 
> ...
> 
>> @@ -49,20 +49,14 @@ static unsigned int mp_hash_shift __ro_after_init;
>> static __initdata unsigned long mhash_entries;
>> static int __init set_mhash_entries(char *str)
>> {
>> -	if (!str)
>> -		return 0;
>> -	mhash_entries = simple_strtoul(str, &str, 0);
>> -	return 1;
>> +	return kstrtoul(str, 0, &mhash_entries) == 0;
>> }
>> __setup("mhash_entries=", set_mhash_entries);
> 
> I'm not very experienced with the cmdline option parsing but AFAICT the
> 'str' argument can be indeed NULL and kstrtoul() will not be happy with
> that?

I don't think 'str' can be NULL. If you don't pass a value, 'str' will
be the empty string (just tested this).

Thanks,
Thorsten