Re: [PATCH v3] vfs: new O_NODE open flag

From: Miklos Szeredi
Date: Thu Dec 03 2009 - 00:46:45 EST

On Wed, 2 Dec 2009, Alan Cox wrote:
> > You're still missing the point. O_NODE is like a hard link, except
> > the reference doesn't come from the filesystem but from a file
> > descriptor. From udev's perspective there's no difference.
> I don't think I am missing the point here. You have a reference to an
> object in the fs but you don't have a reference to the driver underneath
> s the driver can change on you *while* you have the O_NODE open and fd
> live. That cannot happen with a hard link and open.
> It isn't the same thing as far as I can see. You don't have the barrier
> between the operations that occurs in the real open/close case because
> they lock the driver.

The file descriptor opened with O_NODE allows exaclactly the same
operations that a hard link to the device would, nothing more. It's
just a link to the *node*, except it doesn't increment the link count,
the driver is irrelevant.

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