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Date: Tue, 16 May 2017 13:57:23 -0700 (PDT)
From: Stefano Stabellini <sstabellini@...nel.org>
To: Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc: Stefano Stabellini <sstabellini@...nel.org>,
xen-devel@...ts.xen.org, 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 Mon, 15 May 2017, Boris Ostrovsky wrote:
> 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?
Today < 0 means error, 0 means OK but no notifications required, 1 means
OK with notifications. Given that errors are returned to the other end
using the appropriate response field (we don't do anything with an error
in pvcalls_back_work), I could change this to:
-1: no need for notifications (both errors and regular conditions)
0: notifications
> > + 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?
They are meant to handle spurious event notifications. From the Linux
irq handling subsystem point of view, they are not 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').
This is to avoid race conditions. A notification could be delivered
after RING_FINAL_CHECK_FOR_REQUESTS is called, returning more == 0, but
before pvcalls_back_work completes. In that case, without priv->work,
pvcalls_back_work wouldn't be rescheduled because it is still running
and the work would be left undone.
> > + queue_work(priv->wq, &priv->register_work);
> > +
> > return IRQ_HANDLED;
> > }
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