Re: [PATCH 04/18] xen/pvcalls: xenbus state handling

[Stefano Stabellini]

On Mon, 15 May 2017, Boris Ostrovsky wrote:
> On 05/15/2017 04:35 PM, Stefano Stabellini wrote:
> > Introduce the code to handle xenbus state changes.
> > 
> > Implement the probe function for the pvcalls backend. Write the
> > supported versions, max-page-order and function-calls nodes to xenstore,
> > as required by the protocol.
> > 
> > Introduce stub functions for disconnecting/connecting to a frontend.
> > 
> > Signed-off-by: Stefano Stabellini <stefano@xxxxxxxxxxx>
> > CC: boris.ostrovsky@xxxxxxxxxx
> > CC: jgross@xxxxxxxx
> > ---
> >  drivers/xen/pvcalls-back.c | 133
> > +++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 133 insertions(+)
> > 
> > diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> > index 46a889a..86eca19 100644
> > --- a/drivers/xen/pvcalls-back.c
> > +++ b/drivers/xen/pvcalls-back.c
> > @@ -25,6 +25,9 @@
> >  #include <xen/xenbus.h>
> >  #include <xen/interface/io/pvcalls.h>
> > 
> > +#define PVCALLS_VERSIONS "1"
> > +#define MAX_RING_ORDER XENBUS_MAX_RING_GRANT_ORDER
> > +
> >  struct pvcalls_ioworker {
> >  	struct work_struct register_work;
> >  	atomic_t io;
> > @@ -45,15 +48,145 @@ static void pvcalls_back_ioworker(struct work_struct
> > *work)
> >  {
> >  }
> > 
> > +static int backend_connect(struct xenbus_device *dev)
> > +{
> > +	return 0;
> > +}
> > +
> > +static int backend_disconnect(struct xenbus_device *dev)
> > +{
> > +	return 0;
> > +}
> > +
> >  static int pvcalls_back_probe(struct xenbus_device *dev,
> >  			      const struct xenbus_device_id *id)
> >  {
> > +	int err;
> > +
> > +	err = xenbus_printf(XBT_NIL, dev->nodename, "versions", "%s",
> > +			    PVCALLS_VERSIONS);
> > +	if (err) {
> > +		pr_warn("%s write out 'version' failed\n", __func__);
> > +		return -EINVAL;
> 
> Why not return err? (below too)

Yeah, I'll make the change.


> > +	}
> > +
> > +	err = xenbus_printf(XBT_NIL, dev->nodename, "max-page-order", "%u",
> > +			    MAX_RING_ORDER);
> > +	if (err) {
> > +		pr_warn("%s write out 'max-page-order' failed\n", __func__);
> > +		return -EINVAL;
> > +	}
> > +
> > +	/* "1" means socket, connect, release, bind, listen, accept and poll*/
> > +	err = xenbus_printf(XBT_NIL, dev->nodename, "function-calls", "1");
> 
> 
> Should "1" be defined in the (public) header file?

Fair enough, it makes sense.

 
> > +	if (err) {
> > +		pr_warn("%s write out 'function-calls' failed\n", __func__);
> > +		return -EINVAL;
> > +	}
> > +
> > +	err = xenbus_switch_state(dev, XenbusStateInitWait);
> > +	if (err)
> > +		return err;
> > +
> >  	return 0;
> >  }
> > 
> > +static void set_backend_state(struct xenbus_device *dev,
> > +			      enum xenbus_state state)
> > +{
> > +	while (dev->state != state) {
> > +		switch (dev->state) {
> > +		case XenbusStateClosed:
> > +			switch (state) {
> > +			case XenbusStateInitWait:
> > +			case XenbusStateConnected:
> > +				xenbus_switch_state(dev, XenbusStateInitWait);
> > +				break;
> > +			case XenbusStateClosing:
> > +				xenbus_switch_state(dev, XenbusStateClosing);
> > +				break;
> > +			default:
> > +				__WARN();
> > +			}
> > +			break;
> > +		case XenbusStateInitWait:
> > +		case XenbusStateInitialised:
> > +			switch (state) {
> > +			case XenbusStateConnected:
> > +				backend_connect(dev);
> > +				xenbus_switch_state(dev,
> > XenbusStateConnected);
> > +				break;
> > +			case XenbusStateClosing:
> > +			case XenbusStateClosed:
> > +				xenbus_switch_state(dev, XenbusStateClosing);
> > +				break;
> > +			default:
> > +				__WARN();
> > +			}
> > +			break;
> > +		case XenbusStateConnected:
> > +			switch (state) {
> > +			case XenbusStateInitWait:
> > +			case XenbusStateClosing:
> > +			case XenbusStateClosed:
> > +				down_write(&pvcalls_back_global.privs_lock);
> > +				backend_disconnect(dev);
> > +				up_write(&pvcalls_back_global.privs_lock);
> 
> 
> Unless you plan to have more stuff under the semaphore, I'd consider putting
> them in backend_disconnect().

Yes, there will be more things in pvcalls_back_fin (the function that
implements module_exit in patch #14).


> > +				xenbus_switch_state(dev, XenbusStateClosing);
> > +				break;
> > +			default:
> > +				__WARN();
> > +			}
> > +			break;
> > +		case XenbusStateClosing:
> > +			switch (state) {
> > +			case XenbusStateInitWait:
> > +			case XenbusStateConnected:
> > +			case XenbusStateClosed:
> > +				xenbus_switch_state(dev, XenbusStateClosed);
> > +				break;
> > +			default:
> > +				__WARN();
> > +			}
> > +			break;
> > +		default:
> > +			__WARN();
> > +		}
> > +	}
> > +}
> > +
> >  static void pvcalls_back_changed(struct xenbus_device *dev,
> >  				 enum xenbus_state frontend_state)
> >  {
> > +	switch (frontend_state) {
> > +	case XenbusStateInitialising:
> > +		set_backend_state(dev, XenbusStateInitWait);
> > +		break;
> > +
> > +	case XenbusStateInitialised:
> > +	case XenbusStateConnected:
> > +		set_backend_state(dev, XenbusStateConnected);
> > +		break;
> > +
> > +	case XenbusStateClosing:
> > +		set_backend_state(dev, XenbusStateClosing);
> > +		break;
> > +
> > +	case XenbusStateClosed:
> > +		set_backend_state(dev, XenbusStateClosed);
> > +		if (xenbus_dev_is_online(dev))
> > +			break;
> > +		/* fall through if not online */
> > +	case XenbusStateUnknown:
> > +		set_backend_state(dev, XenbusStateClosed);
> 
> 
> You are setting XenbusStateClosed twice in case of fallthrough.

I'll fix it.


> > +		device_unregister(&dev->dev);
> > +		break;
> > +
> > +	default:
> > +		xenbus_dev_fatal(dev, -EINVAL, "saw state %d at frontend",
> > +				 frontend_state);
> > +		break;
> > +	}
> >  }
> > 
> >  static int pvcalls_back_remove(struct xenbus_device *dev)
> > 
>