linux-kernel - Re: [PATCH v4 2/2] lib/test-string_helpers.c: add string_get

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Date:	Wed, 16 Sep 2015 13:21:24 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Vitaly Kuznetsov <vkuznets@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Bottomley <JBottomley@...n.com>,
	linux-kernel@...r.kernel.org,
	"K. Y. Srinivasan" <kys@...rosoft.com>
Subject: Re: [PATCH v4 2/2] lib/test-string_helpers.c: add string_get_size() tests

On Tue, Sep 15 2015, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> On Tue, 2015-09-15 at 15:55 +0200, Vitaly Kuznetsov wrote:
>> +static __init void test_string_get_size_one(u64 size, u64 blk_size,
>> +					    const enum 
>> string_size_units units,
>> +					    const char *exp_result)
>> +{
>> +	char buf[16];
>> +
>> +	string_get_size(size, blk_size, units, buf, sizeof(buf));
>> +	if (!memcmp(buf, exp_result, strnlen(exp_result, sizeof(buf) 
>> - 1) + 1))
>
> Actually you don't need to do this +- 1. Either you will have '\0' or
> not, it will be checked by memcmp() anyway.
>
> Thus,
> memcmp(buf, exp_result, strnlen(exp_result, sizeof(buf))).

Huh? How does that ensure that string_get_size put a '\0' at the right
spot? We do need the comparison to also cover the terminating '\0' in
exp_result.

[It would be nice if we could assert at compile-time that
strlen(exp_result) < sizeof(buf).]

> Perhaps one line comment here
> /* Make sure that buf will be always NULL-terminated */
>
>> +	buf[sizeof(buf) - 1] = '\0';

<bikeshed>Could we pretty-please use different names for 0 the pointer
and 0 the character, say in this case nul or NUL or '\0' or simply
0. Also, I don't see the value of the comment; that line is a totally
standard idiom.</bikeshed>.

>> +	pr_warn("expected: %s, got %s\n", exp_result, buf);
>
> Here I recommend to use single quotes (just to see empty strings)
>
> …expected '%s', got '%s'…

Good idea.
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