linux-kernel - Re: printk meeting at LPC

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Date:   Tue, 17 Sep 2019 15:12:04 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        AndreaParri <parri.andrea@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Paul Turner <pjt@...gle.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Peter Zijlstra <peterz@...radead.org>,
        John Ogness <john.ogness@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        LinusTorvalds <torvalds@...ux-foundation.org>,
        Theodore Ts'o <tytso@....edu>,
        PraritBhargava <prarit@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: printk meeting at LPC

On Tue, Sep 17, 2019 at 09:02:54AM -0400, Steven Rostedt wrote:
> On Tue, 17 Sep 2019 09:52:16 +0200
> Petr Mladek <pmladek@...e.com> wrote:
> 
> > Heh, I did some grepping and the return value is actually used on
> > three locations:
> > 
> > $> git grep "= printk("  
> > drivers/scsi/aic7xxx/aic79xx_core.c:	printed = printk("%s[0x%x]", name, value);
> > drivers/scsi/aic7xxx/aic79xx_core.c:		printed += printk(" ");
> > drivers/scsi/aic7xxx/aic79xx_core.c:			printed += printk("%s%s",
> > drivers/scsi/aic7xxx/aic79xx_core.c:		printed += printk(") ");
> > drivers/scsi/aic7xxx/aic79xx_core.c:		printed += printk(" ");
> > drivers/scsi/aic7xxx/aic79xx_core.c:		cur_col = printk("\n%3d FIFO_USE[0x%x] ", SCB_GET_TAG(scb),
> > drivers/scsi/aic7xxx/aic79xx_core.c:		cur_col += printk("SHADDR = 0x%x%x, SHCNT = 0x%x ",
> > drivers/scsi/aic7xxx/aic79xx_core.c:		cur_col += printk("HADDR = 0x%x%x, HCNT = 0x%x ",
> > drivers/scsi/aic7xxx/aic7xxx_core.c:	printed  = printk("%s[0x%x]", name, value);
> > drivers/scsi/aic7xxx/aic7xxx_core.c:		printed += printk(" ");
> > drivers/scsi/aic7xxx/aic7xxx_core.c:			printed += printk("%s%s",
> > drivers/scsi/aic7xxx/aic7xxx_core.c:		printed += printk(") ");
> > drivers/scsi/aic7xxx/aic7xxx_core.c:		printed += printk(" ");
> > drivers/scsi/aic7xxx/aic7xxx_core.c:		cur_col  = printk("\n%3d ", i);
> > drivers/scsi/aic7xxx/aic7xxx_core.c:		cur_col  = printk("\n%3d ", scb->hscb->tag);

All of those can be removed as none of the returned values are used.
What a mess.

> > drivers/scsi/libsas/sas_ata.c:	r = printk("%s" SAS_FMT "ata%u: %s: %pV",

return value is also ignored, this can be fixed.

> > kernel/locking/lockdep.c:			len += printk("%*s   %s", depth, "", usage_str[bit]);
> > kernel/locking/lockdep.c:			len += printk(KERN_CONT " at:\n");

That seems to be the only semi-legitimate use, but if it _really_ needs
it, it can just create the string ahead of time, and use the length then
after it printks it out.

> > It is probably not a big deal. For example, lockdep uses the value
> > just for formatting (extra spaces) when printing backtrace.
> > 
> > I agree that it does not make sense to return the value if it
> > complicates the code too much. Well, we will need to count
> > the string length also from another reason (reservation).
> 
> Well, it's being used. I was thinking of dropping it if it was not.
> Let's keep it then.

I think it should be dropped, only one user of the kernel is using it in
a legitimate way, which kind of implies it isn't needed.

thanks,

greg k-h