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

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Message-id: <20090925190222.GX10562@webber.adilger.int>
Date:	Fri, 25 Sep 2009 13:02:22 -0600
From:	Andreas Dilger <adilger@....com>
To:	Valdis.Kletnieks@...edu
Cc:	"Dr. David Alan Gilbert" <linux@...blig.org>,
	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  13:20 -0400, Valdis.Kletnieks@...edu wrote:
> On Fri, 25 Sep 2009 13:37:47 BST, "Dr. David Alan Gilbert" said:
> 
> > Given an fd opened in this way is it possible to reopen it normally and
> > be guarenteed to get the same object?
> 
> It's not possible even without this flag. Consider:
> 
>         fd1 = open("/tmp/foo",flags);
>         rc = rename("/tmp/foo","/tmp/bar");
>         fd2 = open("/tmp/foo",flags);
> 
> Or were you asking if *absent that sort of tomfoolery* if it would work?

No, the point is that we HAVE an fd that points to the original "/tmp/foo"
opened with O_NODE, and now (after an ioctl, stat, etc) we decide it is
safe to open the file read and/or write without releasing the existing
fd.  The whole point is to AVOID this kind of tomfoolery.

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

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