Re: [PATCH v2 1/6] libxl: add a list of abstract 'channels' to the domain config

[Ian Campbell <Ian.Campbell@citrix.com>]

On Mon, 2014-06-16 at 10:49 +0100, David Scott wrote:
> A 'channel' is a low-bandwidth private communication channel that
> resembles a physical serial port. Example uses include:
> 
>   * providing initial VM configuration without having to use the
>     network
>   * signalling a guest agent
> 
> Every channel has a string 'name' which the VM can use to find
> the appropriate handler. Each channel has an implementation 'type'
> which currently includes:
> 
>   * NONE: reads will block, writes will be thrown away

What's this useful for?

>   * PTY: the I/O surfaces as a pty in the backend domain
>   * PATH: writes are appended to a log file in the backend domain

PATH is quite a generic name for that.

Do reads block?

>   * SOCKET: a listening Unix domain socket accepts a connection in
>     the backend domain and proxies
> 
> Signed-off-by: David Scott <dave.scott@citrix.com>
> ---
>  tools/libxl/libxl_types.idl |   21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
> index 52f1aa9..5671d86 100644
> --- a/tools/libxl/libxl_types.idl
> +++ b/tools/libxl/libxl_types.idl
> @@ -51,6 +51,17 @@ libxl_domain_type = Enumeration("domain_type", [
>      (2, "PV"),
>      ], init_val = -1)
>  
> +libxl_channel_type = Enumeration("channel_type", [
> +    # Connected to nothing:
> +    (0, "NONE"),
> +    # Connect to a pty in the backend domain:
> +    (1, "PTY"),
> +    # Spool output to a file in the backend domain:
> +    (2, "PATH"),
> +    # Listen on a Unix domain socket in the backend domain:
> +    (3, "SOCKET"),
> +    ])
> +
>  libxl_device_model_version = Enumeration("device_model_version", [
>      (0, "UNKNOWN"),
>      (1, "QEMU_XEN_TRADITIONAL"), # Historical qemu-xen device model (qemu-dm)
> @@ -457,6 +468,15 @@ libxl_device_vtpm = Struct("device_vtpm", [
>      ("uuid",             libxl_uuid),
>  ])
>  
> +libxl_device_channel = Struct("device_channel", [
> +    ("backend_domid", libxl_domid),
> +    ("backend_domname", string),
> +    ("devid", libxl_devid),
> +    ("name", string),
> +    ("type", libxl_channel_type),
> +    ("path", string),

Is path valid for all types?

If not then a KeyedUnion would be the way to go.

> +])
> +
>  libxl_domain_config = Struct("domain_config", [
>      ("c_info", libxl_domain_create_info),
>      ("b_info", libxl_domain_build_info),
> @@ -467,6 +487,7 @@ libxl_domain_config = Struct("domain_config", [
>      ("vfbs", Array(libxl_device_vfb, "num_vfbs")),
>      ("vkbs", Array(libxl_device_vkb, "num_vkbs")),
>      ("vtpms", Array(libxl_device_vtpm, "num_vtpms")),
> +    ("channels", Array(libxl_device_channel, "num_channels")),
>  
>      ("on_poweroff", libxl_action_on_shutdown),
>      ("on_reboot", libxl_action_on_shutdown),