linux-kernel - Re: [PATCH] random: Forbid llseek on random chardev

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Date:	Sat, 10 Apr 2010 18:35:30 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] random: Forbid llseek on random chardev

On Sat, Apr 10, 2010 at 11:25:50AM -0500, Matt Mackall wrote:
> On Sat, 2010-04-10 at 16:17 +0200, Frederic Weisbecker wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> > 
> > Seeking on /dev/random and /dev/urandom is pointless.
> 
> It is indeed pointless, though that doesn't mean no one does it. 
> Forbidding a no-op seems a rather unfriendly way to fix this.

I worried about that too. If you think that could break some user
space apps, we can make it a generic_file_llseek.

> > Using generic_file_llseek means we no longer need to
> > take the BKL if anyone tries to seek on these.
> 
> Comment doesn't match the patch?

Oops. I guess the patch has been updated, but not the changelog.

Some background: we are trying to remove the uses of default_llseek
that use the bkl. We started with turning llseek stubs to
generic_file_llseek (or non seekable open in some cases), but we are
hesitating now and think about actually turn all the stubs that
might need the bkl into default_llseek, and fallback to
generic_file_llseek for all other stubs.

Depending on what we do I'll resend you an updated version
of this patch with generic_file_llseek, or I will let the stub
as is.

Thanks.

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