Yi Wang 7b92a36c4c docs: fix syntax issues and struct description in devices

Some description in the device document were inconsistent with the
source code. Also fix some syntax issues to make the sentences more
fluent.

Signed-off-by: Yi Wang <foxywang@tencent.com>

2026-01-14 09:20:34 +00:00

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Inter-VM shared memory device

The Inter-VM shared memory device (ivshmem) is designed to share a memory region between a guest and the host. In order for all guests to be able to pick up the shared memory area, it is modeled as a PCI device exposing said memory to the guest as a PCI BAR.

Device Specification is available at https://www.qemu.org/docs/master/specs/ivshmem-spec.html.

Now we support setting a backend file to share data between host and guest. In other words, we only support ivshmem-plain and ivshmem-doorbell is not supported yet.

Usage

--ivshmem, an optional argument, can be passed to enable ivshmem device. This argument takes a file as a path value and a file size as a size value. The size value must be 2^n.

--ivshmem <ivshmem>  device backend file "path=</path/to/a/file>,size=<file_size>"

Example

Create a file with a size bigger than passed to cloud-hypervisor:

truncate -s 1M /tmp/ivshmem.data

Start application to mmap the file data to a memory region:

./cloud-hypervisor \
    --api-socket /tmp/cloud-hypervisor.sock \
    --kernel vmlinux \
    --disk path=focal-server-cloudimg-amd64.raw \
    --cpus boot=4 \
    --memory size=1024M \
    --ivshmem path=/tmp/ivshmem.data,size=1M

Insmod an ivshmem device driver to enable the device. The file data will be mmapped to the PCI bar2 of ivshmem device, guest can r/w data by accessing this memory.

A simple example of ivshmem driver can be obtained from: https://github.com/lisongqian/clh-linux/commits/ch-6.12.8-ivshmem

The host process can r/w this data by remapping the /tmp/ivshmem.data.

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Inter-VM shared memory device

Usage

Example

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