Expose a read-only host file/partition to a Firecracker microVM with the virtio-pmem device (persistent memory), including snapshot-coherent usage
domain: firecracker-microvm.github.io · 5 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
vhost-user unsupported for pmem; use the virtio-pmem device configured via PUT /pmem/{id} with id, path_on_host and read_only (pmem is read-only) before starting the VM
curl --unix-socket /tmp/firecracker.socket -X PUT http://localhost/pmem/pmem0 -d '{"id":"pmem0","path_on_host":"/mnt/disk.img","read_only":true}'
The guest mounts it as a persistent-memory device (e.g. mount -t ext4 /dev/pmem0 /mnt or a dax mount) for fast read-only access to a host file
Because it is read-only, copy data you want to mutate into a writable virtio-block drive instead
Optionally set a rate_limiter on the pmem device to cap bandwidth
Known gotchas
virtio-pmem mounts are read-only and are generally not snapshot-coherent with the filesystem - for state you must snapshot/write consistently, use a virtio-block device instead
The /pmem/{id} endpoint requires the virtio-pmem device per the dependency matrix
Keep the backing file immutable on the host to preserve the read-only guarantee
Official doc: https://raw.githubusercontent.com/firecracker-microvm/firecracker/main/docs/device-api.md
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