linux-kernel - Re: [PATCH v5 04/13] xen/pvcalls: implement socket command and handle events

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Date:   Tue, 17 Oct 2017 12:59:57 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org
Cc:     linux-kernel@...r.kernel.org, jgross@...e.com,
        Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v5 04/13] xen/pvcalls: implement socket command and handle
 events

On 10/06/2017 08:30 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.
>
> socket_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@...reto.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>

with one question:

> +	/*
> +	 * 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;
> +


Is this ENOTSUPP or EOPNOTSUPP? I didn't know the former even existed
and include/linux/errno.h suggests that this is NFSv3-specific.

-boris