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

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

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@aporeto.com>
> CC: boris.ostrovsky@oracle.com
> CC: jgross@suse.com
> ---
>  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)


> +	}
> +
> +	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?


> +	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().


> +				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.

-boris


> +		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)
>