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Message-ID: <c7d715eb-358a-47a7-95be-c87afc25c8b1@suse.com>
Date: Tue, 13 Jun 2017 09:24:41 +0200
From: Juergen Gross <jgross@...e.com>
To: Stefano Stabellini <sstabellini@...nel.org>,
xen-devel@...ts.xen.org
Cc: linux-kernel@...r.kernel.org, boris.ostrovsky@...cle.com,
Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v3 11/18] xen/pvcalls: implement accept command
On 02/06/17 21:31, Stefano Stabellini wrote:
> Implement the accept command by calling inet_accept. To avoid blocking
> in the kernel, call inet_accept(O_NONBLOCK) from a workqueue, which get
> scheduled on sk_data_ready (for a passive socket, it means that there
> are connections to accept).
>
> Use the reqcopy field to store the request. Accept the new socket from
> the delayed work function, create a new sock_mapping for it, map
> the indexes page and data ring, and reply to the other end. Allocate an
> ioworker for the socket.
>
> Only support one outstanding blocking accept request for every socket at
> any time.
>
> Add a field to sock_mapping to remember the passive socket from which an
> active socket was created.
>
> Signed-off-by: Stefano Stabellini <stefano@...reto.com>
> CC: boris.ostrovsky@...cle.com
> CC: jgross@...e.com
> ---
> drivers/xen/pvcalls-back.c | 109 ++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 108 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> index a75586e..f1173f4 100644
> --- a/drivers/xen/pvcalls-back.c
> +++ b/drivers/xen/pvcalls-back.c
> @@ -65,6 +65,7 @@ struct pvcalls_ioworker {
> struct sock_mapping {
> struct list_head list;
> struct pvcalls_fedata *priv;
> + struct sockpass_mapping *sockpass;
> struct socket *sock;
> uint64_t id;
> grant_ref_t ref;
> @@ -275,10 +276,79 @@ static int pvcalls_back_release(struct xenbus_device *dev,
>
> static void __pvcalls_back_accept(struct work_struct *work)
> {
> + struct sockpass_mapping *mappass = container_of(
> + work, struct sockpass_mapping, register_work);
> + struct sock_mapping *map;
> + struct pvcalls_ioworker *iow;
> + struct pvcalls_fedata *priv;
> + struct socket *sock;
> + struct xen_pvcalls_response *rsp;
> + struct xen_pvcalls_request *req;
> + int notify;
> + int ret = -EINVAL;
> + unsigned long flags;
> +
> + priv = mappass->priv;
> + /* We only need to check the value of "cmd" atomically on read. */
> + spin_lock_irqsave(&mappass->copy_lock, flags);
> + req = &mappass->reqcopy;
> + if (req->cmd != PVCALLS_ACCEPT) {
> + spin_unlock_irqrestore(&mappass->copy_lock, flags);
> + return;
> + }
> + spin_unlock_irqrestore(&mappass->copy_lock, flags);
What about:
req = &mappass->reqcopy;
if (ACCESS_ONCE(req->cmd) != PVCALLS_ACCEPT)
return;
I can't see the need for taking a lock here.
> +
> + sock = sock_alloc();
> + if (sock == NULL)
> + goto out_error;
> + sock->type = mappass->sock->type;
> + sock->ops = mappass->sock->ops;
> +
> + ret = inet_accept(mappass->sock, sock, O_NONBLOCK, true);
> + if (ret == -EAGAIN) {
> + sock_release(sock);
> + goto out_error;
> + }
> +
> + map = pvcalls_new_active_socket(priv,
> + req->u.accept.id_new,
> + req->u.accept.ref,
> + req->u.accept.evtchn,
> + sock);
> + if (!map) {
> + sock_release(sock);
> + goto out_error;
> + }
> +
> + map->sockpass = mappass;
> + iow = &map->ioworker;
> + atomic_inc(&map->read);
> + atomic_inc(&map->io);
> + queue_work_on(iow->cpu, iow->wq, &iow->register_work);
> +
> +out_error:
> + rsp = RING_GET_RESPONSE(&priv->ring, priv->ring.rsp_prod_pvt++);
> + rsp->req_id = req->req_id;
> + rsp->cmd = req->cmd;
> + rsp->u.accept.id = req->u.accept.id;
> + rsp->ret = ret;
> + RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&priv->ring, notify);
> + if (notify)
> + notify_remote_via_irq(priv->irq);
> +
> + spin_lock_irqsave(&mappass->copy_lock, flags);
> + mappass->reqcopy.cmd = 0;
> + spin_unlock_irqrestore(&mappass->copy_lock, flags);
ACCESS_ONCE(mappass->reqcopy.cmd) = 0;
> }
>
> static void pvcalls_pass_sk_data_ready(struct sock *sock)
> {
> + struct sockpass_mapping *mappass = sock->sk_user_data;
> +
> + if (mappass == NULL)
> + return;
> +
> + queue_work(mappass->wq, &mappass->register_work);
> }
>
> static int pvcalls_back_bind(struct xenbus_device *dev,
> @@ -380,7 +450,44 @@ static int pvcalls_back_listen(struct xenbus_device *dev,
> static int pvcalls_back_accept(struct xenbus_device *dev,
> struct xen_pvcalls_request *req)
> {
> - return 0;
> + struct pvcalls_fedata *priv;
> + struct sockpass_mapping *mappass;
> + int ret = -EINVAL;
> + struct xen_pvcalls_response *rsp;
> + unsigned long flags;
> +
> + priv = dev_get_drvdata(&dev->dev);
> +
> + mappass = radix_tree_lookup(&priv->socketpass_mappings,
> + req->u.accept.id);
> + if (mappass == NULL)
> + goto out_error;
> +
> + /*
> + * Limitation of the current implementation: only support one
> + * concurrent accept or poll call on one socket.
> + */
> + spin_lock_irqsave(&mappass->copy_lock, flags);
> + if (mappass->reqcopy.cmd != 0) {
> + spin_unlock_irqrestore(&mappass->copy_lock, flags);
> + ret = -EINTR;
> + goto out_error;
> + }
> +
> + mappass->reqcopy = *req;
This time you need the lock, however you should use:
ACCESS_ONCE(mappass->reqcopy) = *req;
> + spin_unlock_irqrestore(&mappass->copy_lock, flags);
> + queue_work(mappass->wq, &mappass->register_work);
> +
> + /* Tell the caller we don't need to send back a notification yet */
> + return -1;
> +
> +out_error:
> + rsp = RING_GET_RESPONSE(&priv->ring, priv->ring.rsp_prod_pvt++);
> + rsp->req_id = req->req_id;
> + rsp->cmd = req->cmd;
> + rsp->u.accept.id = req->u.accept.id;
> + rsp->ret = ret;
> + return ret;
return 0?
Juergen
> }
>
> static int pvcalls_back_poll(struct xenbus_device *dev,
>
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