linux-kernel - Re: [PATCH v2 1/7] lib: string: add functions to case-convert strings

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Date:	Fri, 8 Jul 2016 11:04:49 -0700
From:	Markus Mayer <markus.mayer@...adcom.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Kees Cook <keescook@...omium.org>,
	dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
	linux-acpi@...r.kernel.org, speakup@...ux-speakup.org,
	devel@...verdev.osuosl.org, linux-scsi@...r.kernel.org,
	target-devel@...r.kernel.org, linux-pm@...r.kernel.org,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/7] lib: string: add functions to case-convert strings

On 7 July 2016 at 17:19, Rasmus Villemoes <linux@...musvillemoes.dk> wrote:
> On Tue, Jul 05 2016, Markus Mayer <mmayer@...adcom.com> wrote:
>
>> +/**
>> + * strncpytoupper - Copy a length-limited string and convert to uppercase.
>> + * @dst: The buffer to store the result.
>> + * @src: The string to convert to uppercase.
>> + * @len: Maximum string length. May be 0 to set no limit.
>> + *
>> + * Returns pointer to terminating '\0' in @dst.
>> + */
>> +char *strncpytoupper(char *dst, const char *src, size_t len)
>> +{
>> +     size_t i;
>> +
>> +     for (i = 0; src[i] != '\0' && (i < len || !len); i++)
>> +             dst[i] = toupper(src[i]);
>> +     if (i < len || !len)
>> +             dst[i] = '\0';
>> +
>> +     return dst + i;
>> +}
>
> Hm, this seems to copy the insane semantics from strncpy of not
> guaranteeing '\0'-termination.

Yeah. I've been tossing that one around a bit. The reason I did it
this way in the end is due to the use cases I found. strncpy() is
being used there and I was a little wary to make too many changes all
at once.

But I understand your point. I'll look at it again and see what
changes might be required in the code that used strncpy() before.

> Why use 0 as a sentinel, when (size_t)-1 == SIZE_MAX would work just as
> well and require a little less code (no || !len)?

I'll change that.

> I regret suggesting this return semantics and now agree that void would
> be better, especially since there doesn't seem to be anyone who can
> use this (or any other) return value. How about
>
> if (!len)
>    return;
>
> for (i = 0; i < len && src[i]; ++i)
>   dst[i] = toupper(src[i]);
> dst[i < len ? i : i-1] = '\0';

This makes sense.

> (I think you must do i < len before testing src[i], since the len
> parameter should be an upper bound on the number of bytes to access in
> both src and dst).
>
> Rasmus

Thanks,
-Markus