The mmap
modules are used for fast memory transfers
between client and server when both reside on the same host.
| Component | Link | |-------------------|----------------------------------------------------------------------------------------------------| | client | xpra.client.mixins.mmap | | client connection | xpra.server.source.mmap | | server | xpra.server.mixins.mmap |
The client and server should expose the following capabilities in
their hello
packet using the clipboard
prefix.
The client creates an mmap
backing file, writes a random
token at a random position within this mmap area and sends the following
capabilities:
| Capability | Value |
|---------------|--------------------------------------| |
file
| path to the mmap backing file | | size
| size of the mmap area | | token
| random token value
generated | | token_index
| position where the token was
written | | token_bytes
| length of the token in bytes
|
The server should attempt to open the mmap file specified, and verify that the token is found.
To use this mmap file, it must write a new token and return this
information to the client. (using the same format, excluding the
file
and size
that the client has already
specified)
The client then verifies that the mmap file can be used bi-directionally.
There are no specific mmap
packets used,
mmap
is used as an encoding.
Xpra can use mmap
with virtio-shmem
to
speed up connections between a host and guest or even between two
guests.
Example steps for host to guest setup:
shmem
device to your VM, ie:
DEV_NAME="shmem-xpra"
virt-install --shmem name="${DEV_NAME}",model.type=ivshmem-plain,size.unit=M,size=512"`)
echo 1 > $(find /sys/devices/ -type f -name "resource2_wc" -exec dirname "{}" \;)/enable
and start an xpra server with mmap
pointing to it:
VSOCK_PORT=10000
MMAP_PATH=$(find /sys/devices/ -type f -name "resource2_wc")
xpra start --bind-vsock=auto:${VSOCK_PORT} --mmap=$MMAP_PATH
mmap
with the same device:
DEV_NAME="shmem-xpra"
VSOCK_PORT=10000
VM_CID=$(virsh dumpxml "${DEV_NAME}" | grep cid | sed 's/[^0-9]*//g')
xpra attach vsock://"${VM_CID}":${VSOCK_PORT}/ -d mmap --mmap="/dev/shm/${DEV_NAME}"
Documentation: