linux-kernel - Re: [patch 00/13] vfs: add helpers to check r/o bind mounts

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Date:	Thu, 24 Apr 2008 10:55:17 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	viro@...IV.linux.org.uk, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, ezk@...sunysb.edu,
	mhalcrow@...ibm.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 00/13] vfs: add helpers to check r/o bind mounts

On Thu, 2008-04-24 at 17:37 +0200, Miklos Szeredi wrote:
> Why are those so important?  Yes, if we have multiple vfs_() calls,
> surround them with an extra want/drop pair.  We do already do multiple
> overlapping want/drop pairs with O_TRUNC and O_CREAT (AFAIR).

The one that I remember is the pair that we take for O_CREAT and the
nameidata_to_filp() in do_filp_open() that we do on it after the
creation and hold while the file is open.

The only reason for this one is that we want to shut down a potential
race that would allow the file to be created, then still return a -EROFS
because someone did a r/w->r/o transition between the create an the
nameidata_to_filp().

We could pass some information into nameidata_to_filp()->__dentry_open()
telling it that we already have a write and it doesn't need to take one,
but I think having the two nested writes is cleaner.

Is that the case you're thinking of?

-- Dave

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