linux-kernel - Re: Q: a_ops->readpage() && struct file

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Message-ID: <20120613191928.GB14246@redhat.com>
Date:	Wed, 13 Jun 2012 21:19:28 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	linuxppc-dev@...ts.ozlabs.org, lkml <linux-kernel@...r.kernel.org>,
	michael@...erman.id.au, antonb@...nktux.localdomain,
	Paul Mackerras <paulus@...ba.org>, benh@...nel.crashing.org,
	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>
Subject: Re: Q: a_ops->readpage() && struct file

On 06/13, Peter Zijlstra wrote:
>
> On Mon, 2012-06-11 at 21:09 +0200, Oleg Nesterov wrote:
> > Stupid question. I'm afraid the answer is "no" but I'll ask anyway.
> > Is it safe to pass filp == NULL to mapping->readpage()? In fact
> > I do not understand why it needs "struct file*" and I do not see
> > any example of actual usage.
>
> Looking at afs_readpage it looks like its OK to pass in NULL. Same for
> nfs_readpage. They use the file, if provided, to avoid some lookups, but
> seem to deal with not having it.

Yes, and reiser4 does the same.

> This answer by example is of course not authorative nor complete.

Yes... perhaps we should simply change this code to use NULL and
collect the bug-reports ;)

Oleg.

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