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Re: [Xen-devel] [PATCH v2 03/13] xen/pvcalls: implement socket command and handle events
On 7/25/2017 5:22 PM, 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@xxxxxxxxxxx>
CC: boris.ostrovsky@xxxxxxxxxx
CC: jgross@xxxxxxxx
---
drivers/xen/pvcalls-front.c | 94 +++++++++++++++++++++++++++++++++++++++++++++
drivers/xen/pvcalls-front.h | 8 ++++
2 files changed, 102 insertions(+)
create mode 100644 drivers/xen/pvcalls-front.h
diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 5e0b265..d1dbcf1 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -20,6 +20,8 @@
#include <xen/xenbus.h>
#include <xen/interface/io/pvcalls.h>
+#include "pvcalls-front.h"
+
#define PVCALLS_INVALID_ID (UINT_MAX)
#define RING_ORDER XENBUS_MAX_RING_GRANT_ORDER
#define PVCALLS_NR_REQ_PER_RING __CONST_RING_SIZE(xen_pvcalls, XEN_PAGE_SIZE)
@@ -40,9 +42,101 @@ 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, done = 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);
These two lines can be combined (both src and dst)
+ 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);
+
+ done = 1;
+ bedata->ring.rsp_cons++;
+ }
+
+ RING_FINAL_CHECK_FOR_RESPONSES(&bedata->ring, more);
+ if (more)
+ goto again;
+ if (done)
+ wake_up(&bedata->inflight_req);
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);
+ 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)
"!= 0" can be dropped
-boris
+ 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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