linux-kernel - Re: [RFC][PATCH 1/2] pin kern mounts as writable

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Message-ID: <20090912134211.GC5858@ZenIV.linux.org.uk>
Date:	Sat, 12 Sep 2009 14:42:11 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: [RFC][PATCH 1/2] pin kern mounts as writable

On Mon, Aug 03, 2009 at 02:59:40PM -0700, Dave Hansen wrote:

> If we are going to continue to use mnt_clone_write() inside
> of init_file(), then we're going to need some kind of extra
> handling.
> 
> What I want to do in the next patch is add a debugging check
> in mnt_clone_write() to double-check that there *is* a real
> writer on the mount before mnt_clone_write() succeeds.  To
> do that, we either need to check for MS_KERNMOUNT around
> that debug check, or we need to make sure that these kern
> mounts *have* a write already.
> 
> I'm choosing to make sure they always have a write.

> +	err = mnt_want_write(mnt);
> +	WARN_ON(err);

And what would happen to that when we do it to a filesystem that is
made read-only by its ->get_sb()?
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