Re: [PATCH v2] implement libvirt-like 'channels' via PV consoles

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Jun 16, 2014 at 10:49:49AM +0100, David Scott wrote:
> Several libvirt applications (e.g. oVirt, CloudStack) make use of 'channels':
> low-bandwidth private host <-> guest communication links which resemble serial
> ports. Typical uses include:
> 
>   * initial VM configuration without using the network: read the config data
>     directly from the channel on boot
> 
>   * controlling a guest agent: signal shutdown reqests, exchange clipboard data,
>     trigger resolution changes
> 
> This patch set re-uses the existing PV console protocol implemented by qemu
> to provide this service.
> 
> If you declare a channel in your .xl file as follows:
> 
>   channel = [ "type=socket,path=/tmp/mysock,name=guest-agent" ]
> 
> then an extra PV console will be added to your guest. This console has the
> extra key in the frontend
> 
>   name = guest-agent
> 
> which allows udev scripts in the VM to create a named device in a well-known
> location (e.g. /dev/xen-channels/guest-agent, similar to the KVM /dev/vports).

Are these udev scripts somewhere implemented?

Thanks!

> The qemu process in the backend domain will proxy the data to/from the named
> Unix domain socket (in this case /tmp/mysock).
> 
> Note this mechanism is intended for low-bandwidth communication only. If an
> application requires a high-bandwith connection then it should use a direct
> vchan connection (and not proxy it via a qemu).
> 
> Changes since v1:
> 
>   * extend xl.cfg(5)
>   * add docs/misc/channel.txt
>   * libxl_types.idl: omit unnecessary init_val = 0
>   * xl_cmdimpl.c: fixed over-long lines
>   * xl_cmdimpl.c: use xrealloc (via ARRAY_EXTEND_INIT)
>   * xl_cmdimpl.c: exit() on parse failure rather than ignore configuration
>   * libxl_create.c: use libxl__device_console_init instead of memset
>   * libxl_create.c: use libxl__strdup(NOGC rather than raw strdup
>   * libxl.c: add name=<name> to console frontend
>   * libxl.c: resolve the backend_domid from backend_domname
>   * libxl_dm.c: channels[i].devid rather than i
>   * libxl_dm.c: fix indentation
>   * libxl_dm.c: use GCSPRINTF convenience macro
> 
> Signed-off-by: David Scott <dave.scott@citrix.com>
> 
> 
> 
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