Re: [PATCH v4 04/13] xen/pvcalls: implement socket command and handle events

From: Boris Ostrovsky
Date: Thu Sep 21 2017 - 13:44:14 EST




+
+static inline int get_request(struct pvcalls_bedata *bedata, int *req_id)
+{
+ *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)
+ return -EAGAIN;
+ return 0;
+}
+
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;
+
+ pvcalls_enter;
+ bedata = dev_get_drvdata(&dev->dev);
+ if (bedata == NULL) {
+ pvcalls_exit;
+ 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;
+ dst = (uint8_t *)&bedata->rsp[req_id] + sizeof(rsp->req_id);
+ src = (uint8_t *)rsp + 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);
+
+ 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);
+ pvcalls_exit;
return IRQ_HANDLED;
}
+int pvcalls_front_socket(struct socket *sock)
+{
+ struct pvcalls_bedata *bedata;
+ struct sock_mapping *map = NULL;
+ struct xen_pvcalls_request *req;
+ int notify, req_id, ret;
+
+ pvcalls_enter;


Can you define enter/exit macros with parentheses (i.e. "pvcalls_enter/exit()')?


+ if (!pvcalls_front_dev) {
+ pvcalls_exit;
+ 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) {
+ pvcalls_exit;
+ return -ENOTSUPP;
+ }


This can be done without entering pvcalls. I think you can enter pvcalls at least right before grabbing socket lock (you may need to move dev_get_drvdata() lower).

(possibly in later patches too)


+
+ bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
+
+ map = kzalloc(sizeof(*map), GFP_KERNEL);
+ if (map == NULL) {
+ pvcalls_exit;
+ return -ENOMEM;
+ }
+
+ spin_lock(&bedata->socket_lock);
+
+ ret = get_request(bedata, &req_id);
+ if (ret < 0) {
+ kfree(map);
+ spin_unlock(&bedata->socket_lock);
+ pvcalls_exit;
+ return ret;
+ }
+
+ /*
+ * sock->sk->sk_send_head is not used for ip sockets: reuse the
+ * field to store a pointer to the struct sock_mapping
+ * corresponding to the socket. This way, we can easily get the
+ * struct sock_mapping from the struct socket.
+ */
+ sock->sk->sk_send_head = (void *)map;
+ list_add_tail(&map->list, &bedata->socket_mappings);
+
+ req = RING_GET_REQUEST(&bedata->ring, req_id);
+ req->req_id = req_id;
+ req->cmd = PVCALLS_SOCKET;
+ req->u.socket.id = (uint64_t) map;
+ req->u.socket.domain = AF_INET;
+ req->u.socket.type = SOCK_STREAM;
+ req->u.socket.protocol = IPPROTO_IP;
+
+ bedata->ring.req_prod_pvt++;
+ RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&bedata->ring, notify);
+ spin_unlock(&bedata->socket_lock);
+ if (notify)
+ notify_remote_via_irq(bedata->irq);
+
+ wait_event(bedata->inflight_req,
+ READ_ONCE(bedata->rsp[req_id].req_id) == req_id);
+
+ 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);

Now that I looked at what *_ONCE macros do I am not sure this is needed, given the smp_mb() above. In pvcalls_front_event_handler() too. And, in fact, in get_request() as well.

(Again, this will probably be also applicable to subsequent patches)

-boris