linux-kernel - Re: [PATCH 1/2] lib/strtox: introduce kstrtoull

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Date: Tue, 19 Dec 2023 14:17:26 +1100
From: David Disseldorp <ddiss@...e.de>
To: Qu Wenruo <quwenruo.btrfs@....com>
Cc: Qu Wenruo <wqu@...e.com>, linux-btrfs@...r.kernel.org, Andrew Morton
 <akpm@...ux-foundation.org>, Christophe JAILLET
 <christophe.jaillet@...adoo.fr>, Andy Shevchenko
 <andriy.shevchenko@...ux.intel.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] lib/strtox: introduce kstrtoull_suffix() helper

On Tue, 19 Dec 2023 06:22:42 +1030, Qu Wenruo wrote:

> On 2023/12/18 23:29, David Disseldorp wrote:
> > Hi Qu,
> >
> > On Fri, 15 Dec 2023 19:09:23 +1030, Qu Wenruo wrote:
> >  
> [...]
> >> +/**
> >> + * kstrtoull_suffix - convert a string to ull with suffixes support
> >> + * @s: The start of the string. The string must be null-terminated, and may also
> >> + *  include a single newline before its terminating null.
> >> + * @base: The number base to use. The maximum supported base is 16. If base is
> >> + *  given as 0, then the base of the string is automatically detected with the
> >> + *  conventional semantics - If it begins with 0x the number will be parsed as a
> >> + *  hexadecimal (case insensitive), if it otherwise begins with 0, it will be
> >> + *  parsed as an octal number. Otherwise it will be parsed as a decimal.
> >> + * @res: Where to write the result of the conversion on success.
> >> + * @suffixes: A string of acceptable suffixes, must be provided. Or caller
> >> + *  should use kstrtoull() directly.  
> >
> > The suffixes parameter seems a bit cumbersome; callers need to provide
> > both upper and lower cases, and unsupported characters aren't checked
> > for. However, I can't think of any better suggestions at this stage.
> >  
> 
> Initially I went bitmap for the prefixes, but it's not any better.
> 
> Firstly where the bitmap should start. If we go bit 0 for "K", then the
> code would introduce some difference between the bit number and left
> shift (bit 0, left shift 10), which may be a little confusing.
> 
> If we go bit 1 for "K", the bit and left shift it much better, but bit 0
> behavior would be left untouched.
> 
> Finally the bitmap itself is not that straightforward.

One benefit from a bitmap would be that unsupported @suffixes are easier
to detect (instead of ignored), but I think if you rename the function
kstrtoull_unit_suffix() then it should be pretty clear what's supported.

> The limitation of providing both upper and lower case is due to the fact
> that we don't have a case insensitive version of strchr().
> But I think it's not that to fix, just convert them all to lower or
> upper case, then do the strchr().
> 
> Would accepting both cases for the suffixes be good enough?

I think so.

Cheers, David