Re: [Xen-devel] [PATCH v5 for-4.5 1/2] libxl: add support for 'channels'

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

David Scott writes ("[PATCH v5 for-4.5 1/2] libxl: add support for 'channels'"):
> A 'channel':
>   - is a low-bandwidth private communication channel that resembles
>     a physical serial port.
>   - is implemented as a PV console with a well-known string name
>     which is used to hook the channel to the appropriate software
>     in the guest (i.e. some kind of guest agent).
>   - has a backend 'connection' which describes what should happen
>     to the data.

This looks good in principle.

I have a couple of easy quibbles:

You have forgotten to document that you transport the channel name in
xenstore in the subkey `name'.  This should be in your `console.txt'
patch I think, given that xenstore-paths.markdown refers to that for
all the nodes in .../console.

And the interaction between consoles in the console part of the domain
configuration and the channels listed in the channels part, should be
documented.  (Even if it's just that consoles always have no name and
channels always have one.)


I have a harder one:

> +int libxl__init_console_from_channel(libxl__gc *gc,
> +                                     libxl__device_console *console,
> +                                     int dev_num,
> +                                     libxl_device_channel *channel)

AFAICT this function is used to recreate the domain's channel
configuration info for the benefit of libxl's caller (making
enquiries) and setting up the qemu arguments.

But nowadays, following Wei's save/restore/JSON patches, I think we
would expect libxl to retrieve this information from the JSON
configuration.  That is, the console information should be in the
stored JSON config and can be retrieved from there.

(There are also unfortunate security implications to reading the
backend directory like that - if we have a driver domain, the qemu
might get untrustworthy paths.)

Wei, am I right ?


Thanks,
Ian.

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