[ovs-dev] [PATCH] ovn-ctl: Initialize the databases.

[Ben Pfaff]

On Mon, Sep 19, 2016 at 11:18:20AM -0700, Guru Shetty wrote:
> On 19 September 2016 at 11:08, Ben Pfaff <blp at ovn.org> wrote:
> 
> > On Sun, Sep 18, 2016 at 11:26:52PM -0700, Gurucharan Shetty wrote:
> > > Without initializing the databases, commands of the form
> > > 'ovn-nbctl --wait=sb ls-add ls0' will simply hang.
> > >
> > > Signed-off-by: Gurucharan Shetty <guru at ovn.org>
> >
> > It's better if the separate initialization step is optional.
> 
> We do this everytime for OVS in do_start_ovsdb of utilities/ovs-ctl.in with:
> ovs_vsctl -- init -- set Open_vSwitch . db-version="$schemaver"
> 
> Is there a subtlety here?

Setting the db-version isn't something that happens automatically, but
the ovs-vsctl "init" command is a no-op, literally an empty function,
because do_vsctl() always does what it would do:

    ovs = ovsrec_open_vswitch_first(idl);
    if (!ovs) {
        /* XXX add verification that table is empty */
        ovs = ovsrec_open_vswitch_insert(txn);
    }

So the first call to ovs-vsctl, regardless of what command it is, should
initialize the database enough for everything else to work.

It looks to me like ovn-sbctl and ovn-nbctl are the same way.

(Don't get me wrong, I think it's better if the databases are
initialized explicitly.  But I also think it's nice if stuff doesn't
hang if, for example, a database gets blanked out through data loss or
admin mistake.)

> >   I think
> > that ovn-nbctl and ovn-sbctl should be initializing the databases
> > automatically when any command runs, if they are not already
> > initialized; that's what ovs-vsctl does, at least.  Is that missing?
> >
> 
> It does initialize when a command is run. But no-one runs ovn-sbctl
> commands right (unless for debugging)?. So any ovn-nbctl command that is
> run with --wait=sb will hang.

I see.

I think that we can make ovn-northd do the initialization too.  It's
pretty trivial: just create an {NB,SB}_Global record if there's none at
the moment.  Then if the databases get cleared, the system recovers.

So: I think that we should initialize the databases, but I also think
that ovn-northd should be capable of it too.