linux-kernel - Re: [PATCH v2] kunit: fix failure to build without printk

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Message-ID: <20190902125249.qs7ql54vnsgf2665@pathway.suse.cz>
Date:   Mon, 2 Sep 2019 14:52:49 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Brendan Higgins <brendanhiggins@...gle.com>
Cc:     Tim.Bird@...y.com, sfr@...b.auug.org.au, frowand.list@...il.com,
        sergey.senozhatsky@...il.com, sergey.senozhatsky.work@...il.com,
        rostedt@...dmis.org, kunit-dev@...glegroups.com,
        rdunlap@...radead.org, sboyd@...nel.org, shuah@...nel.org,
        joe@...ches.com, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2] kunit: fix failure to build without printk

On Fri 2019-08-30 16:37:10, Brendan Higgins wrote:
> On Fri, Aug 30, 2019 at 11:22:43PM +0000, Tim.Bird@...y.com wrote:
> > > -----Original Message-----
> > > From: Brendan Higgins 
> > > 
> > > On Fri, Aug 30, 2019 at 3:46 PM Joe Perches <joe@...ches.com> wrote:
> > > >
> > > > On Fri, 2019-08-30 at 21:58 +0000, Tim.Bird@...y.com wrote:
> > > > > > From: Joe Perches
> > > > []
> > > > > IMHO %pV should be avoided if possible.  Just because people are
> > > > > doing it doesn't mean it should be used when it is not necessary.
> > > >
> > > > Well, as the guy that created %pV, I of course
> > > > have a different opinion.
> > > >
> > > > > >  then wouldn't it be easier to pass in the
> > > > > > > kernel level as a separate parameter and then strip off all printk
> > > > > > > headers like this:
> > > > > >
> > > > > > Depends on whether or not you care for overall
> > > > > > object size.  Consolidated formats with the
> > > > > > embedded KERN_<LEVEL> like suggested are smaller
> > > > > > overall object size.
> > > > >
> > > > > This is an argument I can agree with.  I'm generally in favor of
> > > > > things that lessen kernel size creep. :-)
> > > >
> > > > As am I.
> > > 
> > > Sorry, to be clear, we are talking about the object size penalty due
> > > to adding a single parameter to a function. Is that right?
> > 
> > Not exactly.  The argument is that pre-pending the different KERN_LEVEL
> > strings onto format strings can result in several versions of nearly identical strings
> > being compiled into the object file.  By parameterizing this (that is, adding
> > '%s' into the format string, and putting the level into the string as an argument),
> > it prevents this duplication of format strings.
> > 
> > I haven't seen the data on duplication of format strings, and how much this
> > affects it, but little things can add up.  Whether it matters in this case depends
> > on whether the format strings that kunit uses are also used elsewhere in the kernel,
> > and whether these same format strings are used with multiple kernel message levels.
> >  -- Tim
> 
> I thought this portion of the discussion was about whether Joe's version
> of kunit_printk was better or my critique of his version of kunit_printk:
> 
> Joe's:
> > > > > -void kunit_printk(const char *level,
> > > > > -		  const struct kunit *test,
> > > > > -		  const char *fmt, ...)
> > > > > +void kunit_printk(const struct kunit *test, const char *fmt, ...)
> > > > >  {
> > > > > +	char lvl[PRINTK_MAX_SINGLE_HEADER_LEN + 1] = "\0";
> > > > >  	struct va_format vaf;
> > > > >  	va_list args;
> > > > > +	int kern_level;
> > > > >
> > > > >  	va_start(args, fmt);
> > > > >
> > > > > +	while ((kern_level = printk_get_level(fmt)) != 0) {
> > > > > +		size_t size = printk_skip_level(fmt) - fmt;
> > > > > +
> > > > > +		if (kern_level >= '0' && kern_level <= '7') {
> > > > > +			memcpy(lvl, fmt,  size);
> > > > > +			lvl[size] = '\0';
> > > > > +		}
> > > > > +		fmt += size;
> > > > > +	}
> > > > > +
> > > > >  	vaf.fmt = fmt;
> > > > >  	vaf.va = &args;
> > > > >
> > > > > -	kunit_vprintk(test, level, &vaf);
> > > > > +	printk("%s\t# %s %pV\n", lvl, test->name, &vaf);
> > > > >
> > > > >  	va_end(args);
> > > > >  }
> 
> Mine:
> >  void kunit_printk(const char *level,
> >  		  const struct kunit *test,
> >  		  const char *fmt, ...)
> >  {
> >  	struct va_format vaf;
> >  	va_list args;
> > 
> >  	va_start(args, fmt);
> > 
> > +	fmt = printk_skip_headers(fmt);
> > +
> >  	vaf.fmt = fmt;
> >  	vaf.va = &args;
> > 
> > -	kunit_vprintk(test, level, &vaf);
> > +	printk("%s\t# %s %pV\n", level, test->name, &vaf);
> > 
> >  	va_end(args);
> >  }
> 
> I thought you and Joe were arguing that "Joe's" resulted in a smaller
> object size than "Mine" (not to be confused with the actual patch I
> presented here, which is what Sergey suggested I do on a different
> thread).
> 
> I really don't feel strongly about what Sergey suggested I do (which is
> what this patch originally introduced), versus, what Joe suggested,
> versus what I suggested in response to Joe (or any of the things
> suggested on other threads). I just want to pick one, fix the breakage
> in linux-next, and move on with my life.

I am a bit lost in all the versions ;-) Though, I like most this
patch. I think that it is based on Sergey's suggestion.

I think that object size is not a huge concern for unit testing.
Also if I get it correctly, the object is bigger only when
the same string is used with different log levels. I am not
sure how often this happen.

Feel free to use for this patch:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr

> Cheers