linux-kernel - Re: [PATCH v7 4/4] lib: test_bitmap: add bitmap_print_to

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Message-ID: <YPgHtJqXi8cKad1Q@kroah.com>
Date:   Wed, 21 Jul 2021 13:40:36 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Stefano Brivio <sbrivio@...hat.com>,
        "Ma, Jianpeng" <jianpeng.ma@...el.com>,
        Valentin Schneider <valentin.schneider@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Guodong Xu <guodong.xu@...aro.org>, tangchengchang@...wei.com,
        "Zengtao (B)" <prime.zeng@...ilicon.com>,
        yangyicong <yangyicong@...wei.com>, tim.c.chen@...ux.intel.com,
        Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH v7 4/4] lib: test_bitmap: add bitmap_print_to_buf test
 cases

On Thu, Jul 15, 2021 at 04:23:32PM -0700, Yury Norov wrote:
> On Fri, Jul 16, 2021 at 12:32:45AM +0300, Andy Shevchenko wrote:
> > On Thu, Jul 15, 2021 at 11:48 PM Yury Norov <yury.norov@...il.com> wrote:
> > > On Thu, Jul 15, 2021 at 03:09:39PM +0300, Andy Shevchenko wrote:
> > > > On Thu, Jul 15, 2021 at 11:58:56PM +1200, Barry Song wrote:
> > > > > The added test items cover both cases where bitmap buf of the printed
> > > > > result is greater than and less than 4KB.
> > > > > And it also covers the case where offset for bitmap_print_to_buf is
> > > > > non-zero which will happen when printed buf is larger than one page
> > > > > in sysfs bin_attribute.
> > > >
> > > > More test cases is always a good thing, thanks!
> > >
> > > Generally yes. But in this case... I believe, Barry didn't write that
> > > huge line below by himself. Most probably he copy-pasted the output of
> > > his bitmap_print_buf() into the test. If so, this code tests nothing,
> > > and just enforces current behavior of snprintf.
> > 
> > I'm not sure I got what you are telling me. The big line is to test
> > strings that are bigger than 4k.
> 
> I'm trying to say that human are not able to verify correctness of
> this line. The test is supposed to check bitmap_print_to_buf(), but
> reference output itself is generated by bitmap_print_to_buf(). This
> test will always pass by design, even if there's an error somewhere
> in the middle, isn't it?

Then please manually check it to verify it is correct or not.  Once we
have it verified, that's fine, it will remain static in this test for
always going forward.

That's what "oracles" are for, there is nothing wrong with this test
case or "proof" that I can see.

> > 
> > ...
> > 
> > > > > +static const char large_list[] __initconst = /* more than 4KB */
> > > > > +   "0,4,8,12,16,20,24,28,32-33,36-37,40-41,44-45,48-49,52-53,56-57,60-61,64,68,72,76,80,84,88,92,96-97,100-101,104-1"
> > > > > +   "05,108-109,112-113,116-117,120-121,124-125,128,132,136,140,144,148,152,156,160-161,164-165,168-169,172-173,176-1"
> > > > > +   "77,180-181,184-185,188-189,192,196,200,204,208,212,216,220,224-225,228-229,232-233,236-237,240-241,244-245,248-2"
> > >
> > > I don't like this behavior of the code: each individual line is not a
> > > valid bitmap_list. I would prefer to split original bitmap and print
> > > list representation of parts in a compatible format; considering a
> > > receiving part of this splitting machinery.
> > 
> > I agree that split is not the best here, but after all it's only 1
> > line and this is on purpose.
> 
> What I see is that bitmap_print_to_buf() is called many times,

That is not what the above list shows at all, it's one long string all
together, only split up to make it easier for us to work with.

> and
> each time it returns something that is not a valid bitmap list string.
> If the caller was be able to concatenate all the lines returned by
> bitmap_print_to_buf(), he'd probably get correct result. But in such
> case, why don't he use scnprintf("pbl") directly?

I do not understand the objection here at all.  This series is fixing a
real problem that people are having and your complaining about test
strings is _VERY_ odd.

If you have an alternate solution, please propose it, otherwise I will
be taking this series in the next few days.

thanks,

greg k-h