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-Xen PV Channels
-===============
-
-A channel is a low-bandwidth private byte stream similar to a serial
-link. Typical uses of channels are
-
- 1. to provide initial configuration information to a VM on boot
- (example use: CloudStack's cloud-early-config service)
- 2. to signal/query an in-guest agent
- (example use: oVirt's guest agent)
-
-Channels are similar to virtio-serial devices and emulated serial links.
-Channels are intended to be used in the implementation of libvirt <channel>s
-when running on Xen.
-
-Note: if an application requires a high-bandwidth link then it should use
-vchan instead.
-
-How to use channels: an example
--------------------------------
-
-Consider a cloud deployment where VMs are cloned from pre-made templates,
-and customised on first boot by an in-guest agent which sets the IP address,
-hostname, ssh keys etc. To install the system the cloud administrator would
-first:
-
- 1. Install a guest as normal (no channel configuration necessary)
- 2. Install the in-guest agent specific to the cloud software. This will
- prepare the guest to communicate over the channel, and also prepare
- the guest to be cloned safely (sometimes known as "sysprepping")
- 3. Shutdown the guest
- 4. Register the guest as a template with the cloud orchestration software
- 5. Install the cloud orchestration agent in dom0
-
-At runtime, when a cloud tenant requests that a VM is created from the template,
-the sequence of events would be: (assuming a Linux domU)
-
- 1. A VM is "cloned" from the template
- 2. A unique Unix domain socket path in dom0 is allocated
- (e.g. /my/cloud/software/talk/to/domain/<vm uuid>)
- 3. Domain configuration is created for the VM, listing the channel
- name expected by the in-guest agent. In xl syntax this would be:
-
- channel = [ "connection=socket, name=org.my.cloud.software.agent.version1,
- path = /my/cloud/software/talk/to/domain/<vm uuid>" ]
-
- 4. The VM is started
- 5. In dom0 the cloud orchestration agent connects to the Unix domain
- socket, writes a handshake message and waits for a reply
- 6. Assuming the guest kernel has CONFIG_HVC_XEN_FRONTEND set then the console
- driver will generate a hotplug event
- 7. A udev rule is activated by the hotplug event.
-
- The udev rule would look something like:
-
- SUBSYSTEM=="xen", DEVPATH=="/devices/console-[0-9]", RUN+="xen-console-setup"
-
- where the "xen-console-setup" script would read the channel name and
- make a symlink in /dev/xen-channel/org.my.cloud.software.agent.version1
-
- 8. The in-guest agent uses inotify to see the creation of the /dev/xen-channel
- symlink and opens the device.
- 9. The in-guest agent completes the handshake with the dom0 agent
- 10. The dom0 agent transmits the unique VM configuration: hostname, IP
- address, ssh keys etc etc
- 11. The in-guest agent receives the configuration and applies it.
-
-Using channels avoids having to use a temporary disk device or network
-connection.
-
-Design recommendations and pitfalls
------------------------------------
-
-It's necessary to install channel-specific software (an "agent") into the guest
-before you can use a channel. By default a channel will appear as a device
-which could be mistaken for a serial port or regular console. It is known
-that some software will proactively seek out serial ports and issue AT commands
-at them; make sure such software is disabled!
-
-Since channels are identified by names, application authors must ensure their
-channel names are unique to avoid clashes. We recommend that channel names
-include parts unique to the application such as a domain names. To assist
-prevent clashes we recommend authors add their names to our global channel
-registry at the end of this document.
-
-Limitations
------------
-
-Hotplug and unplug of channels is not currently implemented.
-
-Channel name registry
----------------------
-
-It is important that channel names are globally unique. To help ensure
-that no-one's name clashes with yours, please add yours to this list.
-
- Key:
- N: Name
- C: Contact
- D: Short description of use, possibly including a URL to your software
- or API
-
- N: org.xenproject.guest.clipboard.0.1
- C: David Scott <dave.scott@citrix.com>
- D: Share clipboard data via an in-guest agent. See:
- http://wiki.xenproject.org/wiki/Clipboard_sharing_protocol
A variant in pod format exists now. Signed-off-by: Olaf Hering <olaf@aepfle.de> --- docs/man/xen-pv-channel.markdown.7 | 106 ------------------------------------- 1 file changed, 106 deletions(-) delete mode 100644 docs/man/xen-pv-channel.markdown.7