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Date: Tue, 25 Jul 2017 13:59:26 -0700 (PDT)
From: Stefano Stabellini <sstabellini@...nel.org>
To: Juergen Gross <jgross@...e.com>
cc: Stefano Stabellini <sstabellini@...nel.org>,
xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org,
boris.ostrovsky@...cle.com,
Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v1 10/13] xen/pvcalls: implement poll command
On Mon, 24 Jul 2017, Juergen Gross wrote:
> On 22/07/17 02:12, Stefano Stabellini wrote:
> > For active sockets, check the indexes and use the inflight_conn_req
> > waitqueue to wait.
> >
> > For passive sockets, send PVCALLS_POLL to the backend. Use the
> > inflight_accept_req waitqueue if an accept is outstanding. Otherwise use
> > the inflight_req waitqueue: inflight_req is awaken when a new response
> > is received; on wakeup we check whether the POLL response is arrived by
> > looking at the PVCALLS_FLAG_POLL_RET flag. We set the flag from
> > pvcalls_front_event_handler, if the response was for a POLL command.
> >
> > In pvcalls_front_event_handler, get the struct socket pointer from the
> > poll id (we previously converted struct socket* to uint64_t and used it
> > as id).
> >
> > Signed-off-by: Stefano Stabellini <stefano@...reto.com>
> > CC: boris.ostrovsky@...cle.com
> > CC: jgross@...e.com
> > ---
> > drivers/xen/pvcalls-front.c | 123 ++++++++++++++++++++++++++++++++++++++++----
> > drivers/xen/pvcalls-front.h | 3 ++
> > 2 files changed, 115 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index 3d1041a..b6cfb7d 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> > @@ -128,17 +128,29 @@ static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
> > rsp = RING_GET_RESPONSE(&bedata->ring, bedata->ring.rsp_cons);
> >
> > req_id = rsp->req_id;
> > - src = (uint8_t *)&bedata->rsp[req_id];
> > - src += sizeof(rsp->req_id);
> > - dst = (uint8_t *)rsp;
> > - dst += sizeof(rsp->req_id);
> > - memcpy(dst, src, sizeof(*rsp) - sizeof(rsp->req_id));
> > - /*
> > - * First copy the rest of the data, then req_id. It is
> > - * paired with the barrier when accessing bedata->rsp.
> > - */
> > - smp_wmb();
> > - WRITE_ONCE(bedata->rsp[req_id].req_id, rsp->req_id);
> > + if (rsp->cmd == PVCALLS_POLL) {
> > + struct socket *sock = (struct socket *) rsp->u.poll.id;
> > + struct sock_mapping *map =
> > + (struct sock_mapping *)
> > + READ_ONCE(sock->sk->sk_send_head);
> > +
> > + set_bit(PVCALLS_FLAG_POLL_RET,
> > + (void *)&map->passive.flags);
>
> Add a barrier here to make sure PVCALLS_FLAG_POLL_INFLIGHT is cleared
> _after_ setting PVCALLS_FLAG_POLL_RET?
Yes, good point, I'll add an smp_wmb() here. A barrier is unnecessary at
the other end (the beginning of pvcalls_front_poll_passive) because of
the conditional instructions creating control dependencies. I'll add a
comment.
> > + clear_bit(PVCALLS_FLAG_POLL_INFLIGHT,
> > + (void *)&map->passive.flags);
> > + } else {
> > + src = (uint8_t *)&bedata->rsp[req_id];
> > + src += sizeof(rsp->req_id);
> > + dst = (uint8_t *)rsp;
> > + dst += sizeof(rsp->req_id);
> > + memcpy(dst, src, sizeof(*rsp) - sizeof(rsp->req_id));
> > + /*
> > + * First copy the rest of the data, then req_id. It is
> > + * paired with the barrier when accessing bedata->rsp.
> > + */
> > + smp_wmb();
> > + WRITE_ONCE(bedata->rsp[req_id].req_id, rsp->req_id);
> > + }
> >
> > bedata->ring.rsp_cons++;
> > wake_up(&bedata->inflight_req);
> > @@ -704,6 +716,95 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> > return ret;
> > }
> >
> > +static unsigned int pvcalls_front_poll_passive(struct file *file,
> > + struct pvcalls_bedata *bedata,
> > + struct sock_mapping *map,
> > + poll_table *wait)
> > +{
> > + int notify, req_id;
> > + struct xen_pvcalls_request *req;
> > +
> > + if (test_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> > + (void *)&map->passive.flags)) {
> > + poll_wait(file, &map->passive.inflight_accept_req, wait);
> > + return 0;
> > + }
> > +
> > + if (test_and_clear_bit(PVCALLS_FLAG_POLL_RET,
> > + (void *)&map->passive.flags))
> > + return POLLIN;
> > +
> > + if (test_and_set_bit(PVCALLS_FLAG_POLL_INFLIGHT,
> > + (void *)&map->passive.flags)) {
> > + poll_wait(file, &bedata->inflight_req, wait);
> > + return 0;
> > + }
> > +
> > + spin_lock(&bedata->pvcallss_lock);
> > + req_id = bedata->ring.req_prod_pvt & (RING_SIZE(&bedata->ring) - 1);
> > + BUG_ON(req_id >= PVCALLS_NR_REQ_PER_RING);
> > + if (RING_FULL(&bedata->ring) ||
> > + READ_ONCE(bedata->rsp[req_id].req_id) != PVCALLS_INVALID_ID) {
> > + spin_unlock(&bedata->pvcallss_lock);
> > + return -EAGAIN;
> > + }
> > + req = RING_GET_REQUEST(&bedata->ring, req_id);
> > + req->req_id = req_id;
> > + req->cmd = PVCALLS_POLL;
> > + req->u.poll.id = (uint64_t) map->sock;
> > +
> > + bedata->ring.req_prod_pvt++;
> > + RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&bedata->ring, notify);
> > + spin_unlock(&bedata->pvcallss_lock);
> > + if (notify)
> > + notify_remote_via_irq(bedata->irq);
> > +
> > + poll_wait(file, &bedata->inflight_req, wait);
> > + return 0;
> > +}
> > +
> > +static unsigned int pvcalls_front_poll_active(struct file *file,
> > + struct pvcalls_bedata *bedata,
> > + struct sock_mapping *map,
> > + poll_table *wait)
> > +{
> > + unsigned int mask = 0;
> > + int32_t in_error, out_error;
> > + struct pvcalls_data_intf *intf = map->active.ring;
> > +
> > + out_error = intf->out_error;
> > + in_error = intf->in_error;
> > +
> > + poll_wait(file, &map->active.inflight_conn_req, wait);
> > + if (pvcalls_front_write_todo(map))
> > + mask |= POLLOUT | POLLWRNORM;
> > + if (pvcalls_front_read_todo(map))
> > + mask |= POLLIN | POLLRDNORM;
> > + if (in_error != 0 || out_error != 0)
> > + mask |= POLLERR;
> > +
> > + return mask;
> > +}
> > +
> > +unsigned int pvcalls_front_poll(struct file *file, struct socket *sock,
> > + poll_table *wait)
> > +{
> > + struct pvcalls_bedata *bedata;
> > + struct sock_mapping *map;
> > +
> > + if (!pvcalls_front_dev)
> > + return POLLNVAL;
> > + bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> > +
> > + map = (struct sock_mapping *) READ_ONCE(sock->sk->sk_send_head);
> > + if (!map)
> > + return POLLNVAL;
> > + if (map->active_socket)
> > + return pvcalls_front_poll_active(file, bedata, map, wait);
> > + else
> > + return pvcalls_front_poll_passive(file, bedata, map, wait);
> > +}
> > +
> > static const struct xenbus_device_id pvcalls_front_ids[] = {
> > { "pvcalls" },
> > { "" }
> > diff --git a/drivers/xen/pvcalls-front.h b/drivers/xen/pvcalls-front.h
> > index de24041..25e05b8 100644
> > --- a/drivers/xen/pvcalls-front.h
> > +++ b/drivers/xen/pvcalls-front.h
> > @@ -20,5 +20,8 @@ int pvcalls_front_recvmsg(struct socket *sock,
> > struct msghdr *msg,
> > size_t len,
> > int flags);
> > +unsigned int pvcalls_front_poll(struct file *file,
> > + struct socket *sock,
> > + poll_table *wait);
> >
> > #endif
> >
>
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