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SubjectRe: [PATCH v3 08/13] xen/pvcalls: implement accept command
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On 07/31/2017 06:57 PM, Stefano Stabellini wrote:
> Introduce a waitqueue to allow only one outstanding accept command at
> any given time and to implement polling on the passive socket. Introduce
> a flags field to keep track of in-flight accept and poll commands.
>
> Send PVCALLS_ACCEPT to the backend. Allocate a new active socket. Make
> sure that only one accept command is executed at any given time by
> setting PVCALLS_FLAG_ACCEPT_INFLIGHT and waiting on the
> inflight_accept_req waitqueue.
>
> Convert the new struct sock_mapping pointer into an uint64_t and use it
> as id for the new socket to pass to the backend.
>
> Check if the accept call is non-blocking: in that case after sending the
> ACCEPT command to the backend store the sock_mapping pointer of the new
> struct and the inflight req_id then return -EAGAIN (which will respond
> only when there is something to accept). Next time accept is called,
> we'll check if the ACCEPT command has been answered, if so we'll pick up
> where we left off, otherwise we return -EAGAIN again.
>
> Note that, differently from the other commands, we can use
> wait_event_interruptible (instead of wait_event) in the case of accept
> as we are able to track the req_id of the ACCEPT response that we are
> waiting.
>
> Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> CC: boris.ostrovsky@oracle.com
> CC: jgross@suse.com
> ---
> drivers/xen/pvcalls-front.c | 111 ++++++++++++++++++++++++++++++++++++++++++++
> drivers/xen/pvcalls-front.h | 3 ++
> 2 files changed, 114 insertions(+)
>
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index b2757f5..f83b910 100644
> --- a/drivers/xen/pvcalls-front.c
> +++ b/drivers/xen/pvcalls-front.c
> @@ -65,6 +65,16 @@ struct sock_mapping {
> #define PVCALLS_STATUS_BIND 1
> #define PVCALLS_STATUS_LISTEN 2
> uint8_t status;
> + /*
> + * Internal state-machine flags.
> + * Only one accept operation can be inflight for a socket.
> + * Only one poll operation can be inflight for a given socket.
> + */
> +#define PVCALLS_FLAG_ACCEPT_INFLIGHT 0
> + uint8_t flags;
> + uint32_t inflight_req_id;
> + struct sock_mapping *accept_map;
> + wait_queue_head_t inflight_accept_req;
> } passive;
> };
> };
> @@ -414,6 +424,107 @@ int pvcalls_front_listen(struct socket *sock, int backlog)
> return ret;
> }
>
> +int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
> +{
> + struct pvcalls_bedata *bedata;
> + struct sock_mapping *map;
> + struct sock_mapping *map2 = NULL;
> + struct xen_pvcalls_request *req;
> + int notify, req_id, ret, evtchn, nonblock;
> +
> + if (!pvcalls_front_dev)
> + return -ENOTCONN;
> + bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
> +
> + map = (struct sock_mapping *) READ_ONCE(sock->sk->sk_send_head);
> + if (!map)
> + return -ENOTSOCK;
> +
> + if (map->passive.status != PVCALLS_STATUS_LISTEN)
> + return -EINVAL;
> +
> + nonblock = flags & SOCK_NONBLOCK;
> + /*
> + * Backend only supports 1 inflight accept request, will return
> + * errors for the others
> + */
> + if (test_and_set_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> + (void *)&map->passive.flags)) {
> + req_id = READ_ONCE(map->passive.inflight_req_id);
> + if (req_id != PVCALLS_INVALID_ID &&
> + READ_ONCE(bedata->rsp[req_id].req_id) == req_id)
> + goto received;
> + if (nonblock)
> + return -EAGAIN;
> + if (wait_event_interruptible(map->passive.inflight_accept_req,
> + !test_and_set_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
> + (void *)&map->passive.flags)))
> + return -EINTR;
> + }
> +
> + spin_lock(&bedata->pvcallss_lock);
> + ret = get_request(bedata, &req_id);
> + if (ret < 0) {
> + spin_unlock(&bedata->pvcallss_lock);
> + return ret;
> + }
> + map2 = kzalloc(sizeof(*map2), GFP_KERNEL);
> + if (map2 == NULL)
> + return -ENOMEM;
> + ret = create_active(map2, &evtchn);
> + if (ret < 0) {
> + kfree(map2);


In the connect patch create_active() frees maps2 (and I had some
comments about it)


> + return -ENOMEM;

Both error paths need an unlock.

> + }
> + list_add_tail(&map2->list, &bedata->socket_mappings);
> +
> + req = RING_GET_REQUEST(&bedata->ring, req_id);
> + req->req_id = req_id;
> + req->cmd = PVCALLS_ACCEPT;
> + req->u.accept.id = (uint64_t) map;
> + req->u.accept.ref = map2->active.ref;
> + req->u.accept.id_new = (uint64_t) map2;
> + req->u.accept.evtchn = evtchn;
> + map->passive.accept_map = map2;
> +
> + 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 (nonblock) {
> + WRITE_ONCE(map->passive.inflight_req_id, req_id);
> + return -EAGAIN;


Would it be worth checking (maybe a few times) whether the response has
come back?


> + }
> +
> + if (wait_event_interruptible(bedata->inflight_req,
> + READ_ONCE(bedata->rsp[req_id].req_id) == req_id))
> + return -EINTR;
> +
> +received:
> + map2 = map->passive.accept_map;

I think this could go to the inflight check in the beginning of this
routine (before the 'goto'). Otherwise map2 has already been assigned above.

> + map2->sock = newsock;
> + newsock->sk = kzalloc(sizeof(*newsock->sk), GFP_KERNEL);
> + if (!newsock->sk) {
> + WRITE_ONCE(bedata->rsp[req_id].req_id, PVCALLS_INVALID_ID);
> + WRITE_ONCE(map->passive.inflight_req_id, PVCALLS_INVALID_ID);
> + pvcalls_front_free_map(bedata, map2);
> + kfree(map2);
> + return -ENOMEM;
> + }
> + WRITE_ONCE(newsock->sk->sk_send_head, (void *)map2);
> +
> + clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT, (void *)&map->passive.flags);
> + wake_up(&map->passive.inflight_accept_req);
> +
> + ret = bedata->rsp[req_id].ret;

You can just return bedata->rsp[req_id].ret;

-boris

> + /* read ret, then set this rsp slot to be reused */
> + smp_mb();
> + WRITE_ONCE(bedata->rsp[req_id].req_id, PVCALLS_INVALID_ID);
> + WRITE_ONCE(map->passive.inflight_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
> index aa8fe10..ab4f1da 100644
> --- a/drivers/xen/pvcalls-front.h
> +++ b/drivers/xen/pvcalls-front.h
> @@ -10,5 +10,8 @@ int pvcalls_front_bind(struct socket *sock,
> struct sockaddr *addr,
> int addr_len);
> int pvcalls_front_listen(struct socket *sock, int backlog);
> +int pvcalls_front_accept(struct socket *sock,
> + struct socket *newsock,
> + int flags);
>
> #endif
>

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