linux-kernel - Re: [PATCH 2/3] usbip: dump the port status difference

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Date:	Mon, 13 Jun 2011 15:12:26 -0700
From:	Joe Perches <joe@...ches.com>
To:	Németh Márton <nm127@...email.hu>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>,
	Matt Mooney <mfm@...eddisk.com>,
	Max Vozeler <max@...terhof.net>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	usbip-devel@...ts.sourceforge.net, devel@...verdev.osuosl.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] usbip: dump the port status difference

On Mon, 2011-06-13 at 23:30 +0200, Németh Márton wrote:
> From: Márton Németh <nm127@...email.hu>
> 
> Change the dump function to
> really show the differences in the status bit changes
> +static void dump_port_status_diff(u32 prev_status, u32 new_status)
>  {
>  	int i = 0;

> -	pr_debug("status %08x:", status);
> +	pr_debug("status %08x -> %08x:", prev_status, new_status);
>  	for (i = 0; i < 32; i++) {
> -		if (status & (1 << i))
> -			pr_debug(" %s", bit_desc[i]);
> +		if (!(prev_status & (1 << i)) &&
> +		      new_status & (1 << i)) {
> +			pr_debug(" +%s", bit_desc[i]);
> +		} else if (prev_status & (1 << i) &&
> +			   !(new_status & (1 << i))) {
> +			pr_debug(" -%s", bit_desc[i]);
> +		} else if (prev_status & (1 << i) &&
> +			   new_status & (1 << i)) {
> +			pr_debug("  %s", bit_desc[i]);
> +		}
>  	}
>  	pr_debug("\n");

trivia:

I think the output isn't quite what you might expect.
It could be interleaved by pr_cont from a different
thread. 

I think this might be a bit more readable as below and
this doesn't use implicit newlines by successive pr_<level>.

static void dump_port_status_diff(u32 old_status, u32 new_status)
{
	int i = 0;
	u32 bit = 1;

	char change;
	pr_debug("status old->new %08x -> %08x\n", old_status, new_status);
	while (bit) {
		u32 old = old_status & bit;
		u32 new = new_status & bit;
		char change;

		if (!old && new)
			change = '+';
		else if (old && !new)
			change = '-';
		else
			change = ' ';
		if (old || new)
			pr_debug(" %c%s\n", change, bit_desc[i]);
		bit <<= 1;
		i++;
  	}
}

I don't know if this is in any sort of fast-path or if
gcc will completely optimize this completely away if
pr_debug isn't declared, but maybe surround the function
implementation with

static void dump_port_status_diff(u32 prev_status, u32 new_status)
{
#ifdef DEBUG
	...
#endif
}


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