netdev - Re: [RFC PATCH 01/14] packet: introduce AF

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Message-ID: <CAF=yD-Jr-w-E3r9BySYmcfH+zaWSrGMXaL4-MoPZqnMB20YDQA@mail.gmail.com>
Date:   Thu, 2 Nov 2017 10:45:43 +0900
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     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>,
        michael.lundkvist@...csson.com, ravineet.singh@...csson.com,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        jesse.brandeburg@...el.com, anjali.singhai@...el.com,
        rami.rosen@...el.com, jeffrey.b.shaw@...el.com,
        ferruh.yigit@...el.com, qi.z.zhang@...el.com
Subject: Re: [RFC PATCH 01/14] packet: introduce AF_PACKET V4 userspace API

On Tue, Oct 31, 2017 at 9:41 PM, Björn Töpel <bjorn.topel@...il.com> wrote:
> From: Björn Töpel <bjorn.topel@...el.com>
>
> This patch adds the necessary AF_PACKET V4 structures for usage from
> userspace. AF_PACKET V4 is a new interface optimized for high
> performance packet processing.
>
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> ---
>  include/uapi/linux/if_packet.h | 65 +++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 64 insertions(+), 1 deletion(-)
>
> +struct tpacket4_queue {
> +       struct tpacket4_desc *ring;
> +
> +       unsigned int avail_idx;
> +       unsigned int last_used_idx;
> +       unsigned int num_free;
> +       unsigned int ring_mask;
> +};
>
>  struct packet_mreq {
> @@ -294,6 +335,28 @@ struct packet_mreq {
>         unsigned char   mr_address[8];
>  };
>
> +/*
> + * struct tpacket_memreg_req is used in conjunction with PACKET_MEMREG
> + * to register user memory which should be used to store the packet
> + * data.
> + *
> + * There are some constraints for the memory being registered:
> + * - The memory area has to be memory page size aligned.
> + * - The frame size has to be a power of 2.
> + * - The frame size cannot be smaller than 2048B.
> + * - The frame size cannot be larger than the memory page size.
> + *
> + * Corollary: The number of frames that can be stored is
> + * len / frame_size.
> + *
> + */
> +struct tpacket_memreg_req {
> +       unsigned long   addr;           /* Start of packet data area */
> +       unsigned long   len;            /* Length of packet data area */
> +       unsigned int    frame_size;     /* Frame size */
> +       unsigned int    data_headroom;  /* Frame head room */
> +};

Existing packet sockets take a tpacket_req, allocate memory and let the
user process mmap this. I understand that TPACKET_V4 distinguishes
the descriptor from packet pools, but could both use the existing structs
and logic (packet_mmap)? That would avoid introducing a lot of new code
just for granting user pages to the kernel.

Also, use of unsigned long can cause problems on 32/64 bit compat
environments. Prefer fixed width types in uapi. Same for pointer in
tpacket4_queue.