Re: Request DLT_/LINKTYPE_ value for vSockets

[Gerard Garcia <ggarcia () deic uab cat>]

On 07/18/2016 11:36 PM, Guy Harris wrote:
> OK, so here's a description of the header, in the style of other pages linked to by the "Link-layer header types" page:
>
> Packet structure
>
> +---------------------------+
> |         Source CID        |
> |         (8 Octets)        |
> +---------------------------+
> |      Destination CID      |
> |         (8 Octets)        |
> +---------------------------+
> |        Source port        |
> |         (4 Octets)        |
> +---------------------------+
> |      Destination port     |
> |         (4 Octets)        |
> +---------------------------+
> |         Operation         |
> |         (2 Octets)        |
> +---------------------------+
> |    Transport header type  |
> |         (2 Octets)        |
> +---------------------------+
> |   Transport header length |
> |         (2 Octets)        |
> +---------------------------+
> |      Transport header     |
> .                           .
> .                           .
> .                           .
> +---------------------------+
> |           Payload         |
> .                           .
> .                           .
> .                           .
>
>
> Description
>
> The source and destination CID fields are in little-endian byte order; they identify the source and destination vsock 
> devices.
>
> The source and destination port fields are in little-endian byte order; they identify XXX.
>
> The operation field is in little-endian byte order; it contains a value that is one of:
>
>         * 1, for a connect operation;
>         * 2, for a disconnect operation;
>         * 3, for a control operation;
>         * 4, for a data transfer operation.
>
> The transport header type field is in little-endian byte order; it contains a value that is one of:
>
>         * 1, if there is no transport header information;
>         * 2, if there is a virtio transport header.
>
> The transport header length field is in little-endian byte order; it indicates how many bytes of transport header 
> follow the length field.  It may be non-zero even if the transport header type field has a value of 1; in that case, 
> the bytes for the transport header should be skipped.
>
> If the transport header type field has a value of 2, the transport header is a virtio transport header:
>
>         {fill in description here}
>
> For packets with an operation field with a value of 4, the payload follows the transport header.
>
> So the questions that remain are:
>
>         1) What do the ports identify?  Different connections on the same vsock device?
They identify a data stream within a vsock device.
>         2) What is the format of the transport header?
It is well described in the virtio vsock specification: 
https://stefanha.github.io/virtio/#x1-2800007 May we just link there?
At some point it will be merged with the official specification 
documents 
(http://docs.oasis-open.org/virtio/virtio/v1.0/virtio-v1.0.html) so the 
link will need to be updated.
>         3) Will the length of the transport header ever change?
We should assume that it may change.

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