linux-kernel - Re: [PATCH 06/18] xen/pvcalls: handle commands from the frontend

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Message-ID: <c4c52c1f-b183-a86f-8db5-ec9bec9e19e0@oracle.com>
Date:   Mon, 15 May 2017 22:06:07 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org
Cc:     linux-kernel@...r.kernel.org, jgross@...e.com,
        Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH 06/18] xen/pvcalls: handle commands from the frontend



On 05/15/2017 04:35 PM, Stefano Stabellini wrote:
> When the other end notifies us that there are commands to be read
> (pvcalls_back_event), wake up the backend thread to parse the command.
>
> The command ring works like most other Xen rings, so use the usual
> ring macros to read and write to it. The functions implementing the
> commands are empty stubs for now.
>
> Signed-off-by: Stefano Stabellini <stefano@...reto.com>
> CC: boris.ostrovsky@...cle.com
> CC: jgross@...e.com
> ---
>  drivers/xen/pvcalls-back.c | 115 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 115 insertions(+)
>
> diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> index 876e577..2b2a49a 100644
> --- a/drivers/xen/pvcalls-back.c
> +++ b/drivers/xen/pvcalls-back.c
> @@ -62,12 +62,127 @@ static void pvcalls_back_ioworker(struct work_struct *work)
>  {
>  }
>
> +static int pvcalls_back_socket(struct xenbus_device *dev,
> +		struct xen_pvcalls_request *req)
> +{
> +	return 0;
> +}
> +
> +static int pvcalls_back_connect(struct xenbus_device *dev,
> +				struct xen_pvcalls_request *req)
> +{
> +	return 0;
> +}
> +
> +static int pvcalls_back_release(struct xenbus_device *dev,
> +				struct xen_pvcalls_request *req)
> +{
> +	return 0;
> +}
> +
> +static int pvcalls_back_bind(struct xenbus_device *dev,
> +			     struct xen_pvcalls_request *req)
> +{
> +	return 0;
> +}
> +
> +static int pvcalls_back_listen(struct xenbus_device *dev,
> +			       struct xen_pvcalls_request *req)
> +{
> +	return 0;
> +}
> +
> +static int pvcalls_back_accept(struct xenbus_device *dev,
> +			       struct xen_pvcalls_request *req)
> +{
> +	return 0;
> +}
> +
> +static int pvcalls_back_poll(struct xenbus_device *dev,
> +			     struct xen_pvcalls_request *req)
> +{
> +	return 0;
> +}
> +
> +static int pvcalls_back_handle_cmd(struct xenbus_device *dev,
> +				   struct xen_pvcalls_request *req)
> +{
> +	int ret = 0;
> +
> +	switch (req->cmd) {
> +	case PVCALLS_SOCKET:
> +		ret = pvcalls_back_socket(dev, req);
> +		break;
> +	case PVCALLS_CONNECT:
> +		ret = pvcalls_back_connect(dev, req);
> +		break;
> +	case PVCALLS_RELEASE:
> +		ret = pvcalls_back_release(dev, req);
> +		break;
> +	case PVCALLS_BIND:
> +		ret = pvcalls_back_bind(dev, req);
> +		break;
> +	case PVCALLS_LISTEN:
> +		ret = pvcalls_back_listen(dev, req);
> +		break;
> +	case PVCALLS_ACCEPT:
> +		ret = pvcalls_back_accept(dev, req);
> +		break;
> +	case PVCALLS_POLL:
> +		ret = pvcalls_back_poll(dev, req);
> +		break;
> +	default:
> +		ret = -ENOTSUPP;
> +		break;
> +	}
> +	return ret;
> +}
> +
>  static void pvcalls_back_work(struct work_struct *work)
>  {
> +	struct pvcalls_back_priv *priv = container_of(work,
> +		struct pvcalls_back_priv, register_work);
> +	int notify, notify_all = 0, more = 1;
> +	struct xen_pvcalls_request req;
> +	struct xenbus_device *dev = priv->dev;
> +
> +	atomic_set(&priv->work, 1);
> +
> +	while (more || !atomic_dec_and_test(&priv->work)) {
> +		while (RING_HAS_UNCONSUMED_REQUESTS(&priv->ring)) {
> +			RING_COPY_REQUEST(&priv->ring,
> +					  priv->ring.req_cons++,
> +					  &req);
> +
> +			if (pvcalls_back_handle_cmd(dev, &req) > 0) {

Can you make handlers make "traditional" returns, i.e. <0 on error and 0 
on success? Or do you really need to distinguish 0 from >0?

> +				RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(
> +					&priv->ring, notify);
> +				notify_all += notify;
> +			}
> +		}
> +
> +		if (notify_all)
> +			notify_remote_via_irq(priv->irq);
> +
> +		RING_FINAL_CHECK_FOR_REQUESTS(&priv->ring, more);
> +	}
>  }
>
>  static irqreturn_t pvcalls_back_event(int irq, void *dev_id)
>  {
> +	struct xenbus_device *dev = dev_id;
> +	struct pvcalls_back_priv *priv = NULL;
> +
> +	if (dev == NULL)
> +		return IRQ_HANDLED;
> +
> +	priv = dev_get_drvdata(&dev->dev);
> +	if (priv == NULL)
> +		return IRQ_HANDLED;

These two aren't errors?

> +
> +	atomic_inc(&priv->work);

Is this really needed? We have a new entry on the ring, so the outer 
loop in pvcalls_back_work() will pick this up (by setting 'more').


-boris

> +	queue_work(priv->wq, &priv->register_work);
> +
>  	return IRQ_HANDLED;
>  }
>
>