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

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Message-id: <20090925165316.GT10562@webber.adilger.int>
Date:	Fri, 25 Sep 2009 10:53:16 -0600
From:	Andreas Dilger <adilger@....com>
To:	"Dr. David Alan Gilbert" <linux@...blig.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Andreas Gruenbacher <agruen@...e.de>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: new O_NODE open flag

On Sep 25, 2009  13:37 +0100, Dr. David Alan Gilbert wrote:
> * Miklos Szeredi (miklos@...redi.hu) wrote:
> > On Fri, 25 Sep 2009, Andreas Gruenbacher wrote:
> > > On Thursday, 24 September 2009 16:51:58 Miklos Szeredi wrote:
> > > > This patch adds a new open flag, O_NODE.  This flag means: open just
> > > > the filesystem node instead of the object referenced by the node.
> > > 
> > > What is the intended use for O_NODE?
> > 
> > It lets userspace file descriptors reference a inode without actually
> > "dereferencing" it to get the underlying object.  This allows for a
> > couple of new things:
> > 
> >  - opening a special file (device/socket/fifo) without side effects
> > 
> >  - opening a symlink
> > 
> >  - opening any type of file without any permission is also possible
> >    (of course the resuling file descriptor may not be read or written)
> > 
> > The above allows fstat(), fchmod(), ioctl(), etc to be used for files
> > previously not possible.
> 
> Given an fd opened in this way is it possible to reopen it normally and
> be guarenteed to get the same object?

That was something I'd be interested in as well.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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