linux-kernel - Re: [PATCH v3] vfs: new O

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Message-ID: <20091202204828.4fa0c108@lxorguk.ukuu.org.uk>
Date:	Wed, 2 Dec 2009 20:48:28 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	unlisted-recipients:; (no To-header on input)
Cc:	miklos@...redi.hu, akpm@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] vfs: new O_NODE open flag

[Ridiculous cc list cleaned]

> > udev defends against it with the specific knowledge that any existing
> > open means the device is open and cannot be unloaded. The combination is
> > required (and some other happenstance properties).
> 
> You're still missing the point.  O_NODE is like a hard link, except
> the reference doesn't come from the filesystem but from a file
> descriptor.  From udev's perspective there's no difference.

I don't think I am missing the point here. You have a reference to an
object in the fs but you don't have a reference to the driver underneath
s the driver can change on you *while* you have the O_NODE open and fd
live. That cannot happen with a hard link and open.

It isn't the same thing as far as I can see. You don't have the barrier
between the operations that occurs in the real open/close case because
they lock the driver.
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