netdev - RE: [PATCH net-next v4] openvswitch: enable NSH support

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Date:   Mon, 21 Aug 2017 09:31:27 +0000
From:   Jan Scheurich <jan.scheurich@...csson.com>
To:     "'Yang, Yi'" <yi.y.yang@...el.com>, 'Jiri Benc' <jbenc@...hat.com>
CC:     "'netdev@...r.kernel.org'" <netdev@...r.kernel.org>,
        "'dev@...nvswitch.org'" <dev@...nvswitch.org>,
        "'blp@....org'" <blp@....org>, "'e@...g.me'" <e@...g.me>
Subject: RE: [PATCH net-next v4] openvswitch: enable NSH support

> 
> The second member of the union should be a variable length array [] of
> struct nsh_md2_tlv
> 
> struct nsh_hdr {
>     ovs_be16 ver_flags_ttl_len;
>     uint8_t mdtype;
>     uint8_t np;
>     ovs_16aligned_be32 path_hdr;
>     union {
>         struct nsh_md1_ctx md1;
>         struct nsh_md2_tlv md2[];
>     };
> };
> 
> That was the original design before Ben removed it due to missing support
> in Microsoft compiler.
> For the Kernel datapath we should go back to that.
> 
> I wonder about the possible 16-bit alignment of the 32-bit fields, though.
> How is that handled in the kernel? Also struct nsh_md1_ctx has 32-bit
> members, which might not be 32-bit aligned in the packet.
> 

One afterthought: 

I think it would be good to add another member to the union to represent unstructured context headers as used, e.g., in the context of push_nsh.

struct nsh_hdr {
    ovs_be16 ver_flags_ttl_len;
    uint8_t mdtype;
    uint8_t np;
    ovs_16aligned_be32 path_hdr;
    union {
        uint8_t ctx_headers[];
        struct nsh_md1_ctx md1;
        struct nsh_md2_tlv md2[];
    };
};