Re: [vmw_vmci RFC 00/11] VMCI for Linux
From: Dor Laor
Date: Wed May 16 2012 - 04:55:28 EST
On 05/16/2012 02:50 AM, Greg KH wrote:
On Tue, May 15, 2012 at 08:06:57AM -0700, Andrew Stiegmann (stieg) wrote:
In an effort to improve the out-of-the-box experience with Linux
kernels for VMware users, VMware is working on readying the Virtual
Machine Communication Interface (vmw_vmci) and VMCI Sockets (vmw_vsock) kernel
modules for inclusion in the Linux kernel. The purpose of this post
is to acquire feedback on the vmw_vmci kernel module. The vmw_vsock
kernel module will be presented in a later post.
VMCI allows virtual machines to communicate with host kernel modules
and the VMware hypervisors. User level applications both in a virtual
machine and on the host can use vmw_vmci through VMCI Sockets, a socket
address family designed to be compatible with UDP and TCP at the
interface level. Today, VMCI and VMCI Sockets are used by the VMware
shared folders (HGFS) and various VMware Tools components inside the
guest for zero-config, network-less access to VMware host services. In
addition to this, VMware's users are using VMCI Sockets for various
applications, where network access of the virtual machine is
restricted or non-existent. Examples of this are VMs communicating
with device proxies for proprietary hardware running as host
applications and automated testing of applications running within
virtual machines.
In a virtual machine, VMCI is exposed as a regular PCI device. The
primary communication mechanisms supported are a point-to-point
bidirectional transport based on a pair of memory-mapped queues, and
asynchronous notifications in the form of datagrams and
doorbells. These features are available to kernel level components
such as HGFS and VMCI Sockets through the VMCI kernel API. In addition
to this, the VMCI kernel API provides support for receiving events
related to the state of the VMCI communication channels, and the
virtual machine itself.
Don't we have something like this already for KVM and maybe Xen?
We have virtio-serial driver for guest-host communication:
http://fedoraproject.org/wiki/Features/VirtioSerial
http://www.linux-kvm.org/page/VMchannel_Requirements
Amit Shah, the writer is CCed as well as kvm-devel.
virtio? Can't you use that code instead of a new block of code that is
only used by vmware users? It has virtual pci devices which should give
you what you want/need here, right?
If not, why doesn't that work for you? Would it be easier to just
extend it?
KVM uses virtio-serial as a pci device which has 'ports' on top of it.
The ports acts like channels that can be created dynamically and allows
guest userspace <-> host userspace communication.
In theory, the kvm mechanism should be a good fit for other hypervisors.
Nevertheless, despite my biased love for KVM, I bet it would be 'tricky'
for VMW to change their hardware model and shift to virtio hardware
abstraction. In addition, they'll be required to change existing apps
that use their socket code.
One can bunker in our rightful requirement of 'upstream first' but this
may slow/vanish the benefits of getting VMW code upstream for out of the
box experience for Linux users.
IMHO, let's be practical and include this pci device (pending standard
review) but _require_ that the VMCI sockets family will be a general
mechanism that may be used over virtio-serial as well.
Andrew, it would be the best to work w/ Amit and various other KVM
hackers to get your (changed) code upstream.
Regards,
Dor
thanks,
greg k-h
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