linux-kernel - Re: [PATCH v3 2/4] lib/hexdump.c: factor out generic hexdump formatting for reuse.

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Message-ID: <20190328090350.GS9224@smile.fi.intel.com>
Date:   Thu, 28 Mar 2019 11:03:50 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "Life is hard, and then you die" <ronald@...ovation.ch>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Henrik Rydberg <rydberg@...math.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Lukas Wunner <lukas@...ner.de>,
        Federico Lorenzi <federico@...velground.com>,
        linux-input <linux-input@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/4] lib/hexdump.c: factor out generic hexdump
 formatting for reuse.

On Wed, Mar 27, 2019 at 05:34:59PM -0700, Life is hard, and then you die wrote:
> 
> On Wed, Mar 27, 2019 at 09:46:48AM +0200, Andy Shevchenko wrote:
> > On Wed, Mar 27, 2019 at 3:49 AM Ronald Tschalär <ronald@...ovation.ch> wrote:
> > >
> > > This introduces print_hex_dump_to_cb() which contains all the hexdump
> > > formatting minus the actual printk() call, allowing an arbitrary print
> > > function to be supplied instead. And print_hex_dump() is re-implemented
> > > using print_hex_dump_to_cb().
> > >
> > > This allows other hex-dump logging functions to be provided which call
> > > printk() differently or even log the hexdump somewhere entirely
> > > different.

> > In any case, don't do it like this. smaller non-recursive printf() is
> > better than one big receursive call.
> > When it looks like an optimization, it's actually a regression.
> 
> Not sure where you see recursion here - are you referring to the
> callback approach?

%pV is a recursive printf().

> Since dev_printk() ends up calling printk with a
> dictionary as well as additional formatting, vs print_hex_dump()'s
> stright use of printk, this seemed like the best way accommodate
> various possible ways of logging the messages. But as per below I
> guess this is moot.

I recommend to read this: https://lwn.net/Articles/780556/

> > And yes, debugfs idea is not bad.
> 
> So it seems like that is the consensus. As per my other response, I'll
> do this then and leave the print_hex_dump() alone.
> 
> > P.S. Also check %*ph specifier.

-- 
With Best Regards,
Andy Shevchenko