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

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Date:	Tue, 15 Sep 2015 09:43:02 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	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

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.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy
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