netdev - Re: [PATCH bpf-next 05/15] xsk: add support for bind for Rx

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Date:   Tue, 24 Apr 2018 12:55:54 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        michael.lundkvist@...csson.com,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Singhai, Anjali" <anjali.singhai@...el.com>,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>
Subject: Re: [PATCH bpf-next 05/15] xsk: add support for bind for Rx

On Mon, Apr 23, 2018 at 9:56 AM, Björn Töpel <bjorn.topel@...il.com> wrote:
> From: Magnus Karlsson <magnus.karlsson@...el.com>
>
> Here, the bind syscall is added. Binding an AF_XDP socket, means
> associating the socket to an umem, a netdev and a queue index. This
> can be done in two ways.
>
> The first way, creating a "socket from scratch". Create the umem using
> the XDP_UMEM_REG setsockopt and an associated fill queue with
> XDP_UMEM_FILL_QUEUE. Create the Rx queue using the XDP_RX_QUEUE
> setsockopt. Call bind passing ifindex and queue index ("channel" in
> ethtool speak).
>
> The second way to bind a socket, is simply skipping the
> umem/netdev/queue index, and passing another already setup AF_XDP
> socket. The new socket will then have the same umem/netdev/queue index
> as the parent so it will share the same umem. You must also set the
> flags field in the socket address to XDP_SHARED_UMEM.
>
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> ---

> +static struct socket *xsk_lookup_xsk_from_fd(int fd, int *err)
> +{
> +       struct socket *sock;
> +
> +       *err = -ENOTSOCK;
> +       sock = sockfd_lookup(fd, err);
> +       if (!sock)
> +               return NULL;
> +
> +       if (sock->sk->sk_family != PF_XDP) {
> +               *err = -ENOPROTOOPT;
> +               sockfd_put(sock);
> +               return NULL;
> +       }
> +
> +       *err = 0;
> +       return sock;
> +}

In this and similar cases, can use ERR_PTR to avoid the extra argument.