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[PATCH v1 03/13] xen/pvcalls: implement socket command and handle events

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  [PATCH v1 03/13] xen/pvcalls: implement socket command and handle events Stefano Stabellini <sstabellini@kernel.org> - 2017-07-22 02:20 +0200
    Re: [PATCH v1 03/13] xen/pvcalls: implement socket command and handle  events Juergen Gross <jgross@suse.com> - 2017-07-24 21:30 +0200
      Re: [PATCH v1 03/13] xen/pvcalls: implement socket command and handle  events Stefano Stabellini <sstabellini@kernel.org> - 2017-07-25 22:50 +0200

#1694064 — [PATCH v1 03/13] xen/pvcalls: implement socket command and handle events

Send a PVCALLS_SOCKET command to the backend, use the masked
req_prod_pvt as req_id. This way, req_id is guaranteed to be between 0
and PVCALLS_NR_REQ_PER_RING. We already have a slot in the rsp array
ready for the response, and there cannot be two outstanding responses
with the same req_id.

Wait for the response by waiting on the inflight_req waitqueue and
check for the req_id field in rsp[req_id]. Use atomic accesses to
read the field. Once a response is received, clear the corresponding rsp
slot by setting req_id to PVCALLS_INVALID_ID. Note that
PVCALLS_INVALID_ID is invalid only from the frontend point of view. It
is not part of the PVCalls protocol.

pvcalls_front_event_handler is in charge of copying responses from the
ring to the appropriate rsp slot. It is done by copying the body of the
response first, then by copying req_id atomically. After the copies,
wake up anybody waiting on waitqueue.

pvcallss_lock protects accesses to the ring.

Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
CC: boris.ostrovsky@oracle.com
CC: jgross@suse.com
---
 drivers/xen/pvcalls-front.c | 91 +++++++++++++++++++++++++++++++++++++++++++++
 drivers/xen/pvcalls-front.h |  8 ++++
 2 files changed, 99 insertions(+)
 create mode 100644 drivers/xen/pvcalls-front.h

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index fb08ebf..7933c73 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -40,9 +40,100 @@ struct pvcalls_bedata {
 
 static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
 {
+	struct xenbus_device *dev = dev_id;
+	struct pvcalls_bedata *bedata;
+	struct xen_pvcalls_response *rsp;
+	uint8_t *src, *dst;
+	int req_id = 0, more = 0;
+
+	if (dev == NULL)
+		return IRQ_HANDLED;
+
+	bedata = dev_get_drvdata(&dev->dev);
+	if (bedata == NULL)
+		return IRQ_HANDLED;
+
+again:
+	while (RING_HAS_UNCONSUMED_RESPONSES(&bedata->ring)) {
+		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);
+
+		bedata->ring.rsp_cons++;
+		wake_up(&bedata->inflight_req);
+	}
+
+	RING_FINAL_CHECK_FOR_RESPONSES(&bedata->ring, more);
+	if (more)
+		goto again;
 	return IRQ_HANDLED;
 }
 
+int pvcalls_front_socket(struct socket *sock)
+{
+	struct pvcalls_bedata *bedata;
+	struct xen_pvcalls_request *req;
+	int notify, req_id, ret;
+
+	if (!pvcalls_front_dev)
+		return -EACCES;
+	/*
+	 * PVCalls only supports domain AF_INET,
+	 * type SOCK_STREAM and protocol 0 sockets for now.
+	 *
+	 * Check socket type here, AF_INET and protocol checks are done
+	 * by the caller.
+	 */
+	if (sock->type != SOCK_STREAM)
+	    return -ENOTSUPP;
+
+	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
+
+	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_SOCKET;
+	req->u.socket.id = (uint64_t) sock;
+	req->u.socket.domain = AF_INET;
+	req->u.socket.type = SOCK_STREAM;
+	req->u.socket.protocol = 0;
+
+	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);
+
+	if (wait_event_interruptible(bedata->inflight_req,
+		READ_ONCE(bedata->rsp[req_id].req_id) == req_id) != 0)
+		return -EINTR;
+
+	ret = bedata->rsp[req_id].ret;
+	/* read ret, then set this rsp slot to be reused */
+	smp_mb();
+	WRITE_ONCE(bedata->rsp[req_id].req_id, PVCALLS_INVALID_ID);
+
+	return ret;
+}
+
 static const struct xenbus_device_id pvcalls_front_ids[] = {
 	{ "pvcalls" },
 	{ "" }
diff --git a/drivers/xen/pvcalls-front.h b/drivers/xen/pvcalls-front.h
new file mode 100644
index 0000000..b7dabed
--- /dev/null
+++ b/drivers/xen/pvcalls-front.h
@@ -0,0 +1,8 @@
+#ifndef __PVCALLS_FRONT_H__
+#define __PVCALLS_FRONT_H__
+
+#include <linux/net.h>
+
+int pvcalls_front_socket(struct socket *sock);
+
+#endif
-- 
1.9.1

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#1695025 — Re: [PATCH v1 03/13] xen/pvcalls: implement socket command and handle events

On 22/07/17 02:11, Stefano Stabellini wrote:
> Send a PVCALLS_SOCKET command to the backend, use the masked
> req_prod_pvt as req_id. This way, req_id is guaranteed to be between 0
> and PVCALLS_NR_REQ_PER_RING. We already have a slot in the rsp array
> ready for the response, and there cannot be two outstanding responses
> with the same req_id.
> 
> Wait for the response by waiting on the inflight_req waitqueue and
> check for the req_id field in rsp[req_id]. Use atomic accesses to
> read the field. Once a response is received, clear the corresponding rsp
> slot by setting req_id to PVCALLS_INVALID_ID. Note that
> PVCALLS_INVALID_ID is invalid only from the frontend point of view. It
> is not part of the PVCalls protocol.
> 
> pvcalls_front_event_handler is in charge of copying responses from the
> ring to the appropriate rsp slot. It is done by copying the body of the
> response first, then by copying req_id atomically. After the copies,
> wake up anybody waiting on waitqueue.
> 
> pvcallss_lock protects accesses to the ring.
> 
> Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> CC: boris.ostrovsky@oracle.com
> CC: jgross@suse.com
> ---
>  drivers/xen/pvcalls-front.c | 91 +++++++++++++++++++++++++++++++++++++++++++++
>  drivers/xen/pvcalls-front.h |  8 ++++
>  2 files changed, 99 insertions(+)
>  create mode 100644 drivers/xen/pvcalls-front.h
> 
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index fb08ebf..7933c73 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c

Shouldn't you include pvcalls-front.h?

> @@ -40,9 +40,100 @@ struct pvcalls_bedata {
>  
>  static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
>  {
> +	struct xenbus_device *dev = dev_id;
> +	struct pvcalls_bedata *bedata;
> +	struct xen_pvcalls_response *rsp;
> +	uint8_t *src, *dst;
> +	int req_id = 0, more = 0;
> +
> +	if (dev == NULL)
> +		return IRQ_HANDLED;
> +
> +	bedata = dev_get_drvdata(&dev->dev);
> +	if (bedata == NULL)
> +		return IRQ_HANDLED;
> +
> +again:
> +	while (RING_HAS_UNCONSUMED_RESPONSES(&bedata->ring)) {
> +		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);
> +
> +		bedata->ring.rsp_cons++;
> +		wake_up(&bedata->inflight_req);
> +	}
> +
> +	RING_FINAL_CHECK_FOR_RESPONSES(&bedata->ring, more);
> +	if (more)
> +		goto again;

Wouldn't it make more sense to use wake_up() just once if there is any
response pending and do the consuming loop outside the irq handler?


Juergen

>  	return IRQ_HANDLED;
>  }
>  
> +int pvcalls_front_socket(struct socket *sock)
> +{
> +	struct pvcalls_bedata *bedata;
> +	struct xen_pvcalls_request *req;
> +	int notify, req_id, ret;
> +
> +	if (!pvcalls_front_dev)
> +		return -EACCES;
> +	/*
> +	 * PVCalls only supports domain AF_INET,
> +	 * type SOCK_STREAM and protocol 0 sockets for now.
> +	 *
> +	 * Check socket type here, AF_INET and protocol checks are done
> +	 * by the caller.
> +	 */
> +	if (sock->type != SOCK_STREAM)
> +	    return -ENOTSUPP;
> +
> +	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> +
> +	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_SOCKET;
> +	req->u.socket.id = (uint64_t) sock;
> +	req->u.socket.domain = AF_INET;
> +	req->u.socket.type = SOCK_STREAM;
> +	req->u.socket.protocol = 0;
> +
> +	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);
> +
> +	if (wait_event_interruptible(bedata->inflight_req,
> +		READ_ONCE(bedata->rsp[req_id].req_id) == req_id) != 0)
> +		return -EINTR;
> +
> +	ret = bedata->rsp[req_id].ret;
> +	/* read ret, then set this rsp slot to be reused */
> +	smp_mb();
> +	WRITE_ONCE(bedata->rsp[req_id].req_id, PVCALLS_INVALID_ID);
> +
> +	return ret;
> +}
> +
>  static const struct xenbus_device_id pvcalls_front_ids[] = {
>  	{ "pvcalls" },
>  	{ "" }
> diff --git a/drivers/xen/pvcalls-front.h b/drivers/xen/pvcalls-front.h
> new file mode 100644
> index 0000000..b7dabed
> --- /dev/null
> +++ b/drivers/xen/pvcalls-front.h
> @@ -0,0 +1,8 @@
> +#ifndef __PVCALLS_FRONT_H__
> +#define __PVCALLS_FRONT_H__
> +
> +#include <linux/net.h>
> +
> +int pvcalls_front_socket(struct socket *sock);
> +
> +#endif
> 

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#1696392 — Re: [PATCH v1 03/13] xen/pvcalls: implement socket command and handle events

On Mon, 24 Jul 2017, Juergen Gross wrote:
> On 22/07/17 02:11, Stefano Stabellini wrote:
> > Send a PVCALLS_SOCKET command to the backend, use the masked
> > req_prod_pvt as req_id. This way, req_id is guaranteed to be between 0
> > and PVCALLS_NR_REQ_PER_RING. We already have a slot in the rsp array
> > ready for the response, and there cannot be two outstanding responses
> > with the same req_id.
> > 
> > Wait for the response by waiting on the inflight_req waitqueue and
> > check for the req_id field in rsp[req_id]. Use atomic accesses to
> > read the field. Once a response is received, clear the corresponding rsp
> > slot by setting req_id to PVCALLS_INVALID_ID. Note that
> > PVCALLS_INVALID_ID is invalid only from the frontend point of view. It
> > is not part of the PVCalls protocol.
> > 
> > pvcalls_front_event_handler is in charge of copying responses from the
> > ring to the appropriate rsp slot. It is done by copying the body of the
> > response first, then by copying req_id atomically. After the copies,
> > wake up anybody waiting on waitqueue.
> > 
> > pvcallss_lock protects accesses to the ring.
> > 
> > Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> > CC: boris.ostrovsky@oracle.com
> > CC: jgross@suse.com
> > ---
> >  drivers/xen/pvcalls-front.c | 91 +++++++++++++++++++++++++++++++++++++++++++++
> >  drivers/xen/pvcalls-front.h |  8 ++++
> >  2 files changed, 99 insertions(+)
> >  create mode 100644 drivers/xen/pvcalls-front.h
> > 
> > diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> > index fb08ebf..7933c73 100644
> > --- a/drivers/xen/pvcalls-front.c
> > +++ b/drivers/xen/pvcalls-front.c
> 
> Shouldn't you include pvcalls-front.h?

Yes


> > @@ -40,9 +40,100 @@ struct pvcalls_bedata {
> >  
> >  static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
> >  {
> > +	struct xenbus_device *dev = dev_id;
> > +	struct pvcalls_bedata *bedata;
> > +	struct xen_pvcalls_response *rsp;
> > +	uint8_t *src, *dst;
> > +	int req_id = 0, more = 0;
> > +
> > +	if (dev == NULL)
> > +		return IRQ_HANDLED;
> > +
> > +	bedata = dev_get_drvdata(&dev->dev);
> > +	if (bedata == NULL)
> > +		return IRQ_HANDLED;
> > +
> > +again:
> > +	while (RING_HAS_UNCONSUMED_RESPONSES(&bedata->ring)) {
> > +		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);
> > +
> > +		bedata->ring.rsp_cons++;
> > +		wake_up(&bedata->inflight_req);
> > +	}
> > +
> > +	RING_FINAL_CHECK_FOR_RESPONSES(&bedata->ring, more);
> > +	if (more)
> > +		goto again;
> 
> Wouldn't it make more sense to use wake_up() just once if there is any
> response pending and do the consuming loop outside the irq handler?

You are definitely right: it's far better to call wake_up() just once
after the consuming loop if there is any response pending. I'll do that.

However, I am not sure there is much to gain in moving the consuming
loop out of the irq handler: it's pretty short and doesn't call any long
running or sleeping functions.



 
> >  	return IRQ_HANDLED;
> >  }
> >  
> > +int pvcalls_front_socket(struct socket *sock)
> > +{
> > +	struct pvcalls_bedata *bedata;
> > +	struct xen_pvcalls_request *req;
> > +	int notify, req_id, ret;
> > +
> > +	if (!pvcalls_front_dev)
> > +		return -EACCES;
> > +	/*
> > +	 * PVCalls only supports domain AF_INET,
> > +	 * type SOCK_STREAM and protocol 0 sockets for now.
> > +	 *
> > +	 * Check socket type here, AF_INET and protocol checks are done
> > +	 * by the caller.
> > +	 */
> > +	if (sock->type != SOCK_STREAM)
> > +	    return -ENOTSUPP;
> > +
> > +	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> > +
> > +	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_SOCKET;
> > +	req->u.socket.id = (uint64_t) sock;
> > +	req->u.socket.domain = AF_INET;
> > +	req->u.socket.type = SOCK_STREAM;
> > +	req->u.socket.protocol = 0;
> > +
> > +	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);
> > +
> > +	if (wait_event_interruptible(bedata->inflight_req,
> > +		READ_ONCE(bedata->rsp[req_id].req_id) == req_id) != 0)
> > +		return -EINTR;
> > +
> > +	ret = bedata->rsp[req_id].ret;
> > +	/* read ret, then set this rsp slot to be reused */
> > +	smp_mb();
> > +	WRITE_ONCE(bedata->rsp[req_id].req_id, PVCALLS_INVALID_ID);
> > +
> > +	return ret;
> > +}
> > +
> >  static const struct xenbus_device_id pvcalls_front_ids[] = {
> >  	{ "pvcalls" },
> >  	{ "" }
> > diff --git a/drivers/xen/pvcalls-front.h b/drivers/xen/pvcalls-front.h
> > new file mode 100644
> > index 0000000..b7dabed
> > --- /dev/null
> > +++ b/drivers/xen/pvcalls-front.h
> > @@ -0,0 +1,8 @@
> > +#ifndef __PVCALLS_FRONT_H__
> > +#define __PVCALLS_FRONT_H__
> > +
> > +#include <linux/net.h>
> > +
> > +int pvcalls_front_socket(struct socket *sock);
> > +
> > +#endif
> > 
> 

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