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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>
53 lines
1.6 KiB
Markdown
53 lines
1.6 KiB
Markdown
# Inter-VM shared memory device
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The Inter-VM shared memory device (ivshmem) is designed to share a memory
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region between a guest and the host. In order for all guests to be able to
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pick up the shared memory area, it is modeled as a PCI device exposing said
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memory to the guest as a PCI BAR.
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Device Specification is available
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at https://www.qemu.org/docs/master/specs/ivshmem-spec.html.
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Now we support setting a backend file to share data between host and guest.
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In other words, we only support ivshmem-plain and ivshmem-doorbell is not
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supported yet.
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## Usage
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`--ivshmem`, an optional argument, can be passed to enable ivshmem device.
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This argument takes a file as a `path` value and a file size as a `size` value.
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The `size` value must be 2^n.
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```
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--ivshmem <ivshmem> device backend file "path=</path/to/a/file>,size=<file_size>"
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```
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## Example
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Create a file with a size bigger than passed to `cloud-hypervisor`:
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```
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truncate -s 1M /tmp/ivshmem.data
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```
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Start application to mmap the file data to a memory region:
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```
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./cloud-hypervisor \
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--api-socket /tmp/cloud-hypervisor.sock \
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--kernel vmlinux \
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--disk path=focal-server-cloudimg-amd64.raw \
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--cpus boot=4 \
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--memory size=1024M \
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--ivshmem path=/tmp/ivshmem.data,size=1M
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```
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Insmod an ivshmem device driver to enable the device. The file data will be
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mmapped to the PCI `bar2` of ivshmem device,
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guest can r/w data by accessing this memory.
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A simple example of ivshmem driver can be obtained from:
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https://github.com/lisongqian/clh-linux/commits/ch-6.12.8-ivshmem
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The host process can r/w this data by remapping the `/tmp/ivshmem.data`.
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