netdev - Re: [ovs-dev] [PATCH net-next] openvswitch: add NSH support

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Date:   Wed, 9 Aug 2017 11:09:12 -0700
From:   Ben Pfaff <blp@....org>
To:     "Yang, Yi Y" <yi.y.yang@...el.com>
Cc:     Jan Scheurich <jan.scheurich@...csson.com>,
        "dev@...nvswitch.org" <dev@...nvswitch.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jiri Benc <jbenc@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Zoltán Balogh <zoltan.balogh@...csson.com>
Subject: Re: [ovs-dev] [PATCH net-next] openvswitch: add NSH support

On Wed, Aug 09, 2017 at 09:41:51AM +0000, Yang, Yi Y wrote:
> Hi,  Jan
> 
> I have worked out a patch, will send it quickly for Ben. In addition, I also will send out a patch to change encap_nsh &decap_nsh to push_nsh and pop_nsh. Per comments from all the people, we all agreed to do so :-)
> 
> diff --git a/datapath/linux/compat/include/linux/openvswitch.h b/datapath/linux/compat/include/linux/openvswitch.h
> index bc6c94b..4936c12 100644
> --- a/datapath/linux/compat/include/linux/openvswitch.h
> +++ b/datapath/linux/compat/include/linux/openvswitch.h
> @@ -793,7 +793,7 @@ struct ovs_action_push_eth {
>         struct ovs_key_ethernet addresses;
>  };
> 
> -#define OVS_ENCAP_NSH_MAX_MD_LEN 16
> +#define OVS_ENCAP_NSH_MAX_MD_LEN 248
>  /*
>   * struct ovs_action_encap_nsh - %OVS_ACTION_ATTR_ENCAP_NSH
>   * @flags: NSH header flags.
> @@ -809,7 +809,7 @@ struct ovs_action_encap_nsh {
>      uint8_t mdlen;
>      uint8_t np;
>      __be32 path_hdr;
> -    uint8_t metadata[OVS_ENCAP_NSH_MAX_MD_LEN];
> +    uint8_t metadata[];
>  };

This brings the overall format of ovs_action_encap_nsh to:

struct ovs_action_encap_nsh {
    uint8_t flags;
    uint8_t mdtype;
    uint8_t mdlen;
    uint8_t np;
    __be32 path_hdr;
    uint8_t metadata[];
};

This is an unusual format for a Netlink attribute.  More commonly, one
would put variable-length data into an attribute of its own, which
allows that data to be handled using the regular Netlink means.  Then
the mdlen and metadata members could be removed, since they would be
part of the additional attribute, and one might expect the mdtype member
to be removed as well since each type of metadata would be in a
different attribute type.

So, a format closer to what I expect to see in Netlink is something like
this:

/**
 * enum ovs_nsh_attr - Metadata attributes for %OVS_ACTION_ENCAP_NSH action.
 *
 * @OVS_NSH_ATTR_MD1: Contains 16-byte NSH type-1 metadata.
 * @OVS_NSH_ATTR_MD2: Contains 0- to 255-byte variable-length NSH type-2
 * metadata. */
enum ovs_nsh_attr {
    OVS_NSH_ATTR_MD1,
    OVS_NSH_ATTR_MD2
};

/*
 * struct ovs_action_encap_nsh - %OVS_ACTION_ATTR_ENCAP_NSH
 *
 * @path_hdr: NSH service path id and service index.
 * @flags: NSH header flags.
 * @np: NSH next_protocol: Inner packet type.
 *
 * Followed by either %OVS_NSH_ATTR_MD1 or %OVS_NSH_ATTR_MD2 attribute.
 */
struct ovs_action_encap_nsh {
    __be32 path_hdr;
    uint8_t flags;
    uint8_t np;
};