Another update to this that adds support for unmap notification. The
device
has also been renamed to `porthole` and now resides here:
https://github.com/gnif/qemu/blob/master/hw/misc/porthole.c
And here is the updated Linux test client.
https://gist.github.com/gnif/77e7fb54604b42a1a98ecb8bf3d2cf46
-Geoff
On 2019-10-31 13:55, ge...@hostfission.com wrote:
Hi Dave,
On 2019-10-31 05:52, Dr. David Alan Gilbert wrote:
* ge...@hostfission.com (ge...@hostfission.com) wrote:
Hi All,
Over the past week, I have been working to come up with a solution to
the
memory transfer performance issues that hinder the Looking Glass
Project.
Currently Looking Glass works by using the IVSHMEM shared memory
device
which
is fed by an application that captures the guest's video output.
While this
works it is sub-optimal because we first have to perform a CPU copy
of the
captured frame into shared RAM, and then back out again for display.
Because
the destination buffers are allocated by closed proprietary code
(DirectX,
or
NVidia NvFBC) there is no way to have the frame placed directly into
the
IVSHMEM shared ram.
This new device, currently named `introspection` (which needs a more
suitable
name, porthole perhaps?), provides a means of translating guest
physical
addresses to host virtual addresses, and finally to the host offsets
in RAM
for
file-backed memory guests. It does this by means of a simple protocol
over a
unix socket (chardev) which is supplied the appropriate fd for the
VM's
system
RAM. The guest (in this case, Windows), when presented with the
address of a
userspace buffer and size, will mlock the appropriate pages into RAM
and
pass
guest physical addresses to the virtual device.
Hi Geroggrey,
I wonder if the same thing can be done by using the existing
vhost-user
mechanism.
vhost-user is intended for implementing a virtio device outside of
the
qemu process; so it has a character device that qemu passes commands
down
to the other process, where qemu mostly passes commands via the virtio
queues. To be able to read the virtio queues, the external process
mmap's the same memory as the guest - it gets passed a 'set mem table'
command by qemu that includes fd's for the RAM, and includes
base/offset
pairs saying that a particular chunk of RAM is mapped at a particular
guest physical address.
Whether or not you make use of virtio queues, I think the mechanism
for the device to tell the external process the mappings might be what
you're after.
Dave
While normally I would be all for re-using such code, the vhost-user
while
being very feature-complete from what I understand is overkill for our
requirements. It will still allocate a communication ring and an events
system
that we will not be using. The goal of this device is to provide a dumb
&
simple method of sharing system ram, both for this project and for
others that
work on a simple polling mechanism, it is not intended to be an
end-to-end
solution like vhost-user is.
If you still believe that vhost-user should be used, I will do what I
can to
implement it, but for such a simple device I honestly believe it is
overkill.
-Geoff
This device and the windows driver have been designed in such a way
that
it's a
utility device for any project and/or application that could make use
of it.
The PCI subsystem vendor and device ID are used to provide a means of
device
identification in cases where multiple devices may be in use for
differing
applications. This also allows one common driver to be used for any
other
projects wishing to build on this device.
My ultimate goal is to get this to a state where it could be accepted
upstream
into Qemu at which point Looking Glass would be modified to use it
instead
of
the IVSHMEM device.
My git repository with the new device can be found at:
https://github.com/gnif/qemu
The new device is:
https://github.com/gnif/qemu/blob/master/hw/misc/introspection.c
Looking Glass:
https://looking-glass.hostfission.com/
The windows driver, while working, needs some cleanup before the
source is
published. I intend to maintain both this device and the windows
driver
including producing a signed Windows 10 driver if Redhat are
unwilling or
unable.
Kind Regards,
Geoffrey McRae
HostFission
https://hostfission.com
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
