linux-kernel - Re: [PATCH v3 2/2] lib/test-string_helpers.c: add string_get

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Date:	Tue, 15 Sep 2015 14:10:43 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	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 v3 2/2] lib/test-string_helpers.c: add string_get_size() tests

Andy Shevchenko <andriy.shevchenko@...ux.intel.com> writes:

> On Tue, 2015-09-15 at 00:00 +0200, Rasmus Villemoes wrote:
>> On Mon, Sep 14 2015, Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>> 
>
> Vitaly, thanks for the test cases. My comments below.
>
>> > +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[256];
>> > +
>> > +	string_get_size(size, blk_size, units, buf, sizeof(buf));
>> > +	if (!strncmp(buf, exp_result, min(sizeof(buf), 
>> > strlen(exp_result))))
>> > +		return;
>> 
>> Nits: It probably makes sense to also test that string_get_size
>> '\0'-terminates the buffer, so I'd spell this
>> 
>>   if (!memcmp(buf, exp_result, min(sizeof(buf), 
>> strlen(exp_result)+1)))
>> 
>> With a generous stack buffer, that min() will always evaluate to the
>> strlen(exp_result)+1. On that note: Maybe 256 is a bit excessive. I
>> don't think this will run very deep in the kernel stack, but the code 
>> might
>> get copy-pasted somewhere else. 16 should be plenty.
>
> Agree with Rasmus.
>
> And just to make a side note that useless use of min() since we have
> strnlen() :-)
>
>> 
>> > +	pr_warn("Test 'test_string_get_size_one' failed!\n");
>> > +	pr_warn("string_get_size(size = %llu, blk_size = %llu, 
>> > units = %d\n",
>> > +		size, blk_size, units);
>> 
>> [There's probably no pretty way of getting from units to a text
>> representation, but it's slightly annoying to have to check the 
>> source
>> for the enum definition to figure out what units=0 or units=1 means.]
>> 
>> > +	pr_warn("expected: %s, got %s\n", exp_result, buf);
>> 
>> In case we failed to '\0'-terminate buf, we might want to print it 
>> with
>> "%.*s", (int)sizeof(buf), buf. But maybe I'm just overly paranoid.
>
> I prefer to put '\0' at the position after we expected have an actual
> '\0'. In this case we always be NULL terminated. I did this for hexdump
> test cases.

Just to check I got your suggestions right:

...
+       if (!memcmp(buf, exp_result, strnlen(exp_result, sizeof(buf) - 1) + 1))
+               return;
+
+       /* NULL terminate buf right after the expected '\0' */
+       buf[strnlen(exp_result, sizeof(buf) - 2) + 1] = '\0';
...

Alternatively, we could have avoided strnlen() by asserting
strlen(exp_result) < sizeof(buf) - 1 at the very beginning.

-- 
  Vitaly
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