linux-kernel - Re: [RFC] O_NOACC: open without any access

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Message-ID: <20090623143408.GA2147@infradead.org>
Date:	Tue, 23 Jun 2009 10:34:08 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	hch@...radead.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	viro@...IV.linux.org.uk, adilger@....com, dhowells@...hat.com,
	alan@...rguk.ukuu.org.uk, akpm@...ux-foundation.org
Subject: Re: [RFC] O_NOACC: open without any access

On Tue, Jun 23, 2009 at 04:12:22PM +0200, Miklos Szeredi wrote:
> > an issue ioctls + stat / etc on it ut not actually read/write it.
> 
> Two differences between open("foo", 3) and open("foo", O_NOACC):
> 
>   1) open with "3" requires _read_and_write_ permissions on foo, but
>      does not allow either read or write.  Not sure what the logic in
>      that, but that's the way it has always been.

Which is a quite sensible requirement if we want to do ioctls.

> 
>   2) open with "3" calls driver's ->open() with any side effect that
>      may have.  Open with O_NOACC doesn't do that, and hence if we
>      want to allow ioctls they need a new interface which gets a
>      "struct path" instead of a "struct file".

Well, we'll need ->open to support ioctls, and I think it's good to go
down that road.

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