Re: Unionmount: proxying the control port

[Sergiu Ivanov]

Hello,

On Tue, Jul 07, 2009 at 08:55:37PM +0300, Sergiu Ivanov wrote:
> It was agreed that unionmount should forward some of the RPCs invoked
> on its control port to the mountee.  Most (if not all) of such RPCs
> are the fsys_* ones.  I've made up a list of RPCs which should be
> proxied in my opinion and I've also added a short explanation as to
> how this proxying should work:

After a some discussion I can build the (more or less) final (and,
BTW, complete) version of the list:

* fsys_startup: this RPC is invoked by the translator on its bootstrap
  port, so forwarding does not make sense for it;

* fsys_goaway: both the unionfs (unionmount) and the mountee should go
  away.

* fsys_getroot: this RPC should be handled completely within unionfs
  to preserve consistency; note that trying to forward this RPC will
  result in a complete vanishing of unionfs, since all lookups will
  actually take place in the mountee's filesystem;

* fsys_getfile: the implementation of this RPC should be left in its
  default version (returning EOPNOTSUPP); why this should be so is
  explained in the preceding discussion;

* fsys_syncfs: both the mountee and unionfs should be synced;

* fsys_set_options: in transparent mode this RPC should be completely
  forwarded to the mountee; in non-transparent mode this RPC should be
  handled in unionfs first and the (possibly) new value for the
  ``--mount'' option should be delegated to the mountee;

* fsys_getpriv:
* fsys_init: fsys.defs says that these RPCs should only be implemented
  by bootstrap filesystems; since unionfs will hardly ever be a
  bootstrap filesystem, these RPCs will not be implemented;

* fsys_forward: in the previous discussion there is a short
  explanation why this RPC should be left implemented in the default
  version (returning EOPNOTSUPP);

* fsys_get_options: in transparent mode this RPC should be completely
  forwarded to the mountee; in non-transparent mode the result should
  be constructed by obtaining the options of the mountee and listing
  them as the value of option ``--mountee'', together with other
  unionfs options.

Regards,
scolobb