linux-kernel - RE: [PATCH 2/4] lib/hexdump.c: Optionally suppress lines of filler bytes

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Message-ID: <0db001d4f376$b598af80$20ca0e80$@d-silva.org>
Date:   Mon, 15 Apr 2019 20:33:47 +1000
From:   "Alastair D'Silva" <alastair@...ilva.org>
To:     "'Petr Mladek'" <pmladek@...e.com>
Cc:     "'Alastair D'Silva'" <alastair@....ibm.com>,
        "'Jani Nikula'" <jani.nikula@...ux.intel.com>,
        "'Joonas Lahtinen'" <joonas.lahtinen@...ux.intel.com>,
        "'Rodrigo Vivi'" <rodrigo.vivi@...el.com>,
        "'David Airlie'" <airlied@...ux.ie>,
        "'Daniel Vetter'" <daniel@...ll.ch>,
        "'Karsten Keil'" <isdn@...ux-pingi.de>,
        "'Jassi Brar'" <jassisinghbrar@...il.com>,
        "'Tom Lendacky'" <thomas.lendacky@....com>,
        "'David S. Miller'" <davem@...emloft.net>,
        "'Jose Abreu'" <Jose.Abreu@...opsys.com>,
        "'Kalle Valo'" <kvalo@...eaurora.org>,
        "'Stanislaw Gruszka'" <sgruszka@...hat.com>,
        "'Benson Leung'" <bleung@...omium.org>,
        "'Enric Balletbo i Serra'" <enric.balletbo@...labora.com>,
        "'James E.J. Bottomley'" <jejb@...ux.ibm.com>,
        "'Martin K. Petersen'" <martin.petersen@...cle.com>,
        "'Greg Kroah-Hartman'" <gregkh@...uxfoundation.org>,
        "'Alexander Viro'" <viro@...iv.linux.org.uk>,
        "'Sergey Senozhatsky'" <sergey.senozhatsky@...il.com>,
        "'Steven Rostedt'" <rostedt@...dmis.org>,
        "'Andrew Morton'" <akpm@...ux-foundation.org>,
        <intel-gfx@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>, <ath10k@...ts.infradead.org>,
        <linux-wireless@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
        <linux-fbdev@...r.kernel.org>, <devel@...verdev.osuosl.org>,
        <linux-fsdevel@...r.kernel.org>
Subject: RE: [PATCH 2/4] lib/hexdump.c: Optionally suppress lines of filler bytes

> > > On Wed 2019-04-10 13:17:18, Alastair D'Silva wrote:
> > > > From: Alastair D'Silva <alastair@...ilva.org>
> > > >
> > > > Some buffers may only be partially filled with useful data, while
> > > > the rest is padded (typically with 0x00 or 0xff).
> > > >
> > > > This patch introduces flags which allow lines of padding bytes to
> > > > be suppressed, making the output easier to interpret:
> > > > HEXDUMP_SUPPRESS_0X00, HEXDUMP_SUPPRESS_0XFF
> > > >
> > > > The first and last lines are not suppressed by default, so the
> > > > function always outputs something. This behaviour can be further
> > > > controlled with the HEXDUMP_SUPPRESS_FIRST &
> > > HEXDUMP_SUPPRESS_LAST flags.
> > > >
> > > > An inline wrapper function is provided for backwards compatibility
> > > > with existing code, which maintains the original behaviour.
> > > >
> > >
> > > > diff --git a/lib/hexdump.c b/lib/hexdump.c index
> > > > b8a164814744..2f3bafb55a44 100644
> > > > --- a/lib/hexdump.c
> > > > +++ b/lib/hexdump.c
> > > > +void print_hex_dump_ext(const char *level, const char *prefix_str,
> > > > +			int prefix_type, int rowsize, int groupsize,
> > > > +			const void *buf, size_t len, u64 flags)
> > > >  {
> > > >  	const u8 *ptr = buf;
> > > > -	int i, linelen, remaining = len;
> > > > +	int i, remaining = len;
> > > >  	unsigned char linebuf[64 * 3 + 2 + 64 + 1];
> > > > +	bool first_line = true;
> > > >
> > > >  	if (rowsize != 16 && rowsize != 32 && rowsize != 64)
> > > >  		rowsize = 16;
> > > >
> > > >  	for (i = 0; i < len; i += rowsize) {
> > > > -		linelen = min(remaining, rowsize);
> > > > +		bool skip = false;
> > > > +		int linelen = min(remaining, rowsize);
> > > > +
> > > >  		remaining -= rowsize;
> > > >
> > > > +		if (flags & HEXDUMP_SUPPRESS_0X00)
> > > > +			skip = buf_is_all(ptr + i, linelen, 0x00);
> > > > +
> > > > +		if (!skip && (flags & HEXDUMP_SUPPRESS_0XFF))
> > > > +			skip = buf_is_all(ptr + i, linelen, 0xff);
> > > > +
> > > > +		if (first_line && !(flags & HEXDUMP_SUPPRESS_FIRST))
> > > > +			skip = false;
> > > > +
> > > > +		if (remaining <= 0 && !(flags &
HEXDUMP_SUPPRESS_LAST))
> > > > +			skip = false;
> > > > +
> > > > +		if (skip)
> > > > +			continue;
> > >
> > > IMHO, quietly skipping lines could cause a lot of confusion,
> > > espcially
> > when the address is not printed.
> > >
> > It's up to the caller to decide how they want it displayed.
> 
> I wonder who would want to quietly skip some data values.
> Are you using it yourself? Could you please provide an example?

Yes, but I don't have the content with me at the moment, so I can't share
it. I'm dumping persistent memory labels, which are 64kB long, but only the
first few hundred bytes are populated.
 
> I do not see why we would need to complicate the API and code by this.
> 
> The behavior proposed by Tvrtko Ursulin makes much more sense. I mean
> https://lkml.kernel.org/r/929244ed-cc7f-b0f3-b5ac-
> 50e798e83188@...ux.intel.com

I agree that is better, I'll add that to V2.

-- 
Alastair D'Silva           mob: 0423 762 819
skype: alastair_dsilva     msn: alastair@...ilva.org
blog: http://alastair.d-silva.org    Twitter: @EvilDeece