Date: Thu, 10 Mar 2011 14:38:06 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Phil Carmody <ext-phil.2.carmody@nokia.com>
Cc: gregkh@suse.de, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv3 1/1] sysfs: add more info to the oops dump
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On Fri, 11 Mar 2011 00:27:07 +0200
Phil Carmody <ext-phil.2.carmody@nokia.com> wrote:

> +static int last_sysfs_write_len;
>  void sysfs_printk_last_file(void)
>  {
> -	printk(KERN_EMERG "last sysfs file: %s\n", last_sysfs_file);
> +	printk(KERN_EMERG "last sysfs file (%c): %s%c",
> +	       (last_sysfs_write_len == SYSFS_NOT_A_WRITE) ? 'r' : 'w',
> +	       last_sysfs_file,
> +	       last_sysfs_write_len > 0 ? ' ' : '\n');
> +	if (last_sysfs_write_len >= (int)sizeof(last_sysfs_write))
> +		printk(KERN_CONT " written: %s...(%d chars)\n",
> +		       last_sysfs_write, last_sysfs_write_len);
> +	else if (last_sysfs_write_len > 0)
> +		printk(KERN_CONT " written: %s\n", last_sysfs_write);
>  }

That's going to fail to emit the \n if last_sysfs_write_len<=0. 
However there are tricks inside printk() which will fix that up if the
next printk starts with KERN_foo.


I can recall just one instance in the past 5-6 years in which the
last-sysfs-file output enabled me to locate a bug which would otherwise
have been unlocatable (within a drivers/md handler, iirc).

I don't think it's a terribly useful feature.  Except for when it _is_
useful, when it's very useful ;) The world wouldn't end if we decided
to remove it.
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