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

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Date:   Fri, 12 Apr 2019 16:03:53 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Alastair D'Silva <alastair@....ibm.com>
Cc:     alastair@...ilva.org, 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.

I wonder how it would look like when we print something like:

    --- skipped XX lines full of 0x00 ---

Then we might even remove the SUPPRESS_FIRST, SUPPRESS_LAST
and the ambiguous QUIET flags.

> +
> +		first_line = false;

This should be above the if (skip).

> +
>  		hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize,
> -				   linebuf, sizeof(linebuf), ascii);
> +				   linebuf, sizeof(linebuf),
> +				   flags & HEXDUMP_ASCII);
>  
>  		switch (prefix_type) {
>  		case DUMP_PREFIX_ADDRESS:
> @@ -272,7 +316,7 @@ void print_hex_dump(const char *level, const char *prefix_str, int prefix_type,
>  		}
>  	}
>  }
> -EXPORT_SYMBOL(print_hex_dump);
> +EXPORT_SYMBOL(print_hex_dump_ext);

We should still export even the original function that
is still used everywhere.

Best Regards,
Petr