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SubjectRe: [PATCH v3 04/13] xen/pvcalls: implement socket command and handle events
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On 07/31/2017 06:57 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 and
> barriers to read the field. Note that the barriers are simple smp
> barriers (as opposed to virt barriers) because they are for internal
> frontend synchronization, not frontend<->backend communication.
>
> 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.
>
> Create a new struct sock_mapping and convert the pointer into an
> uint64_t and use it as id for the new socket to pass to the backend. The
> struct will be fully initialized later on connect or bind. In this patch
> the struct sock_mapping is empty, the fields will be added by the next
> patch.
>
> 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.
>
> Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
> CC: boris.ostrovsky@oracle.com
> CC: jgross@suse.com
> ---
> drivers/xen/pvcalls-front.c | 119 ++++++++++++++++++++++++++++++++++++++++++++
> drivers/xen/pvcalls-front.h | 8 +++
> 2 files changed, 127 insertions(+)
> create mode 100644 drivers/xen/pvcalls-front.h
>
> diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
> index 2afe36d..7c4a7cb 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 PVCALLS_RING_ORDER XENBUS_MAX_RING_GRANT_ORDER
> #define PVCALLS_NR_REQ_PER_RING __CONST_RING_SIZE(xen_pvcalls, XEN_PAGE_SIZE)
> @@ -38,11 +40,128 @@ struct pvcalls_bedata {
> };
> static struct xenbus_device *pvcalls_front_dev;
>
> +struct sock_mapping {
> + bool active_socket;
> + struct list_head list;
> + struct socket *sock;
> +};
> +
> +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;
> +
> + 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;
> + 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);
> 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;
> +
> + 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);
> +
> + map = kzalloc(sizeof(*map), GFP_KERNEL);
> + if (map == NULL)
> + return -ENOMEM;
> + /*
> + * 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.


Is this a safe assumption? Is it conceivable that at some point in the
future sk_send_head might become used?


> + */
> + WRITE_ONCE(sock->sk->sk_send_head, (void *)map);
> +
> + spin_lock(&bedata->pvcallss_lock);
> + list_add_tail(&map->list, &bedata->socket_mappings);
> +
> + ret = get_request(bedata, &req_id);
> + if (ret < 0) {
> + spin_unlock(&bedata->pvcallss_lock);
> + return ret;
What is happening to the mapping you've linked above? Should it be
unlinked and freed? (or defer its creation until we've got a request slot?)

> + }
> + 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 = 0;

IPPROTO_IP?


-boris


> +
> + 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);
> +
> + 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);
> +
> + 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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