linux-kernel - Re: [PATCH v3 0/4] kstrtox: introduce memparse

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Date: Mon, 15 Jan 2024 06:31:05 +1030
From: Qu Wenruo <wqu@...e.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Qu Wenruo <quwenruo.btrfs@....com>
Cc: linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
 akpm@...ux-foundation.org, christophe.jaillet@...adoo.fr,
 David.Laight@...lab.com, ddiss@...e.de, geert@...ux-m68k.org
Subject: Re: [PATCH v3 0/4] kstrtox: introduce memparse_safe()



On 2024/1/15 00:12, Andy Shevchenko wrote:
> On Sun, Jan 07, 2024 at 07:28:27AM +1030, Qu Wenruo wrote:
>> On 2024/1/7 01:04, Andy Shevchenko wrote:
>>> On Thu, Jan 04, 2024 at 09:57:47AM +1030, Qu Wenruo wrote:
> 
> ...
> 
>>> Having test cases is quite good, thanks!
>>> But as I understood what Alexey wanted, is not using the kstrtox files for this.
>>> You can introduce it in the cmdline.c, correct? Just include local "kstrtox.h".
>>
>> Not really possible, all the needed parsing helpers are internal inside
>> kstrtox.c.
> 
> I'm not sure I follow. The functions are available to other library (built-in)
> modules.

Did I miss something?

Firstly neither _parse_integer_fixup_radix() nor _parse_integer_limit() 
is exported to modules. (No EXPORT_SYMBOL() call on them).

Secondly _parse_integer_fixup_radix() and _parse_integer_limit have "_" 
prefix, and is only declared in "lib/kstrtox.h", which means they are 
designed only for internal usage.
If putting memparse_safe() into cmdline.c, at least we would need to 
include local header "kstrtox.h", and I'm not sure if this is any better 
than putting memparse_safe() into kstrtox.[ch].

Finally, I just tried putting memparse_safe() into cmdline.c, and it 
failed at linkage stage, even if that offending file has no call to 
memparse_safe():

   ld: arch/x86/boot/compressed/kaslr.o: in function `memparse_safe':
kaslr.c:(.text+0xbb1): undefined reference to `_parse_integer_fixup_radix'
   ld: kaslr.c:(.text+0xbc5): undefined reference to `_parse_integer'
   ld: arch/x86/boot/compressed/vmlinux: hidden symbol `_parse_integer' 
isn't defined

I can try again but I'm not sure if it's possible to move 
memparse_safe() to cmdline.[ch].

> 
>> Furthermore, this also means memparse() can not be enhanced due to:
>>
>> - Lack of ways to return errors
> 
> What does this mean?

If you want to keep the prototype of memparse() (aka, a drop-in 
enhancement), then there is no good way to indicate the errors like 
overflow at all.

> 
>> - Unable to call the parsing helpers inside cmdline.c
> 
> ??? (see above)
> 
See above.

Thanks,
Qu

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