Re: [PATCH 2/3] Start the mountee in a lazy fashion.

[Carl Fredrik Hammar]

Hi,

On Mon, Aug 17, 2009 at 07:15:09PM +0300, Sergiu Ivanov wrote:
> > > +  mountee_node = netfs_make_node (netfs_root_node->nn);
> > > +  if (!mountee_node)
> > > +    return ENOMEM;
> > > +
> > > +  /* Set the mountee on the new node.
> > > +     Note that the O_READ flag does not actually limit access to the
> > > +     mountee's filesystem considerably.  Whenever a client looks up a
> > > +     node which is not a directory, unionfs will give off a port to
> > > +     the node itself, withouth proxying it.  Proxying happens only for
> > > +     directory nodes.  */
> > 
> > Why are you passing O_READ, anyways?...
> 
> The flags which I pass to start_mountee are used in opening the port
> to the root node of the mountee.  (I'm sure you've noticed this; I'm
> just re-stating it to avoid ambiguities).  Inside unionfs, this port
> is used for lookups *only*, so O_READ should be sufficient for any
> internal unionfs needs.  Ports to files themselves are not proxied by
> unionfs (as the comment reads), so the flags passed here don't
> influence that case.
> 
> Also, unionfs itself uses O_READ when opening directory nodes, too
> (well, it actually uses O_READ | O_NOTRANS, but that's unapplicable in
> our case).

You don't need O_READ to do lookup, only to read the entries of a
directory.  If you don't read the entries you should drop the O_READ,
and in unionfs itself if applicable.

(Note that permission to do lookups is determined entirely by the
*current* permission bits and the UIDs and GIDs the file handle has
been authenticated with, unlike read and write for which permissions
are checked only checked once at open.)

Regards,
  Fredrik