Re: [PATCH] vfs: new O_NODE open flag

Andreas Dilger
2009-09-25T16:53:25Z

On Sep 25, 2009 13:37 +0100, Dr. David Alan Gilbert wrote:
> * Miklos Szeredi (miklos@szeredi.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.