linux-kernel - Re: [PATCH v4] remove no longer use of pdflush interface

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Date:	Wed, 6 Jun 2012 15:50:56 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Wanpeng Li <liwp.linux@...il.com>
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	Rob Landley <rob@...dley.net>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Eric W.Biederman" <ebiederm@...ssion.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	"David S. Miller" <davem@...emloft.net>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan.kim@...il.com>,
	James Morris <james.l.morris@...cle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Michel Lespinasse <walken@...gle.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Gavin Shan <shangw@...ux.vnet.ibm.com>,
	Wanpeng Li <liwp@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4] remove no longer use of pdflush interface

On Wed,  6 Jun 2012 21:38:08 +0800
Wanpeng Li <liwp.linux@...il.com> wrote:

> From: Wanpeng Li <liwp@...ux.vnet.ibm.com>
> 
> Since per-BDI flusher introduced to linux 2.6, pdflush mechanism is not
> used any more. But the old interface of pdflush exported in/proc/sys/vm/
> is still there. In order to take attention to back-compatibility issues,
> printk warning information and return -ENOSYS to notice the users the
> interface is removed.
> 
> ...
>
> +/* notice associated proc obsoleted */

This comment is pretty meaningless - I suggest simply removing it.

> +int pdflush_proc_obsolete(struct ctl_table *table, int write,
> +			void __user *buffer, size_t *lenp, loff_t *ppos)
> +{
> +	printk_once(KERN_WARNING "%s exported in /proc is scheduled for removal\n",
> +			table->procname);
> +	return -ENOSYS;
> +}

No, this immediately breaks /proc/sys/vm/nr_pdflush_threads users.  To
preserve back-compatibility we should copy "0\n" out to userspace and
return 2.

> +EXPORT_SYMBOL(pdflush_proc_obsolete);

This export isn't needed?
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