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[Publicity] Xen 4.4 features for press release

Below is the list of features in 4.4, explained as may be suitable for a press release. Let me know if you have any corrections or improvements.


* Non-Linux driver domains.  One of Xen's unique features is that it
is designed to run drivers inside of VMs, allowing better performance,
security, and flexibility.  Until now, however, the core driver domain
functionality required udev, which is only available in Linux.  This
has been replaced with a daemon, allowing arbitrary OSes to be
used as driver domains.

* Event channel scalability.  Event channels are per-VM resources that
allow VMs to communicate with each other.  These were previously
limited to eithe 1024 or 4096 per domain.  Domain 0 needs several for
each guest VM, so this limited the total number of VMs available to
several hundred.  The new event channel implementation allows hundreds
of thousands of event channels, removing this as a limit on the number
of VMs which can be started.

* Experimental support for PVH mode for guests.  PVH mode combines the
best elements of HVM and PV into a mode which allows Xen to take
advantage of many of the hardware virtualization features without
needing the overhead of simulating an entire physical computer. This
will allow for increased efficiency, as well as reduced footprint in
Linux going forward.

* Improved support for SPICE.  SPICE is a protocol for virtial
desktops which allows a much richer connection than display-only
protocols like VNC.  Xen 4.4 adds support for additional
functionality, including vdagent, clipboard sharing, and USB

* pvgrub2 (external).  Rather than have a custom implementation of
grub for pvgrub, the upstream grub2 project now has a build target
which will construct a bootable PV xen image.  This ensures 100% grub2
compatibility for pvgrub going forward.

* Indirect descriptors for block PV protocol (Linux).  Modern storage
devices work much better with larger chunks of data.  Indirect
descriptors have allowed the size of each individual request to
triple, greatly improving performance when running on fast storage
technologies like SSD and RAID.  This is available in any guest
running Linux 3.11 or higher (regardless of Xen version).

* Improved kexec.  kexec functionality is primarily used when a crash
happens, to allow a special kernel to come in afterwards and collect
information about the cause of the crash, to allow developers to
diagnose and fix the root cause.

* Improved xapi support.  xapi is a separate project written in OCaml,
and relies on the Xen OCaml language bindings to operate well. These
bindings have had a major overhaul, and should result in much better
compatibility and support for distros going forward.

* Experimental support for Guest EFI boot.  EFI is the new booting
standard that is replacing BIOS.  Some operating systems only boot
with EFI; and some features, like SecureBoot, only work with EFI.

* 64-bit Xen on ARM now supports booting guests

* Updated to qemu 1.6 and SeaBIOS

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