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

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Message-Id: <E1MsDQ6-0001cY-92@pomaz-ex.szeredi.hu>
Date:	Mon, 28 Sep 2009 12:25:26 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Valdis.Kletnieks@...edu
CC:	linux@...blig.org, miklos@...redi.hu, agruen@...e.de,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: new O_NODE open flag

On Fri, 25 Sep 2009, Valdis.Kletnieks wrote:
> On Fri, 25 Sep 2009 19:35:23 BST, "Dr. David Alan Gilbert" said:
> 
> > I know it's not possible without this flag, my interest is whether
> > it would be possible WITH this flag to promote an fd opened with the
> > O_NODE to a normal fd, guaranteeing that it's still operating on the
> > same object.
> 
> Well, maybe the question is if we should treat "promote" differently than
> "re-open"?
> 
> (And now I'm wondering what happens if you dup() one of these beasts....)

dup() only duplicates _references_ to an open file, it does not create
a new file.  The same applies to fork().

BTW I just checked, and it is possible to re-open or promote an fd
opened with O_NODE like this:

	char tmp[64];

	fd = open(filename, O_NODE | O_NOACCESS);
	/* ... */
	sprintf(tmp, "/proc/self/fd/%i", fd);
	fd_rw = open(tmp, O_RDWR);

Now fd_rw is guaranteed to refer to the same inode as fd.

Thanks,
Miklos
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