Shared folders

Files shared between your code and the guest over virtio-fs or 9p, filled and read from JavaScript.

A shared folder is a tree of files your code and the guest both see. The guest mounts it with virtio-fs or 9p; your code puts files in and reads them back through vm.shares.

Adding a share

Name the share on the command line with a tag, the name the guest mounts it by:

# virtio-fs
-device vhost-user-fs-pci,tag=host
# 9p
-virtfs local,mount_tag=host,security_model=none

Use virtio-fs where the guest's kernel has it; 9p is there for kernels that don't.

Filling it from JavaScript

const share = vm.shares.get("host");
share.put("input/data.csv", new TextEncoder().encode("a,b\n1,2\n"));
share.mkdir("output");

Mounting it in the guest

# virtio-fs
mount -t virtiofs host /mnt
# 9p
mount -t 9p -o trans=virtio host /mnt

Alpine's netboot initramfs loads the driver first: modprobe virtiofs.

Reading the guest's files

const bytes = vm.shares.get("host").get("output/result.txt");
if (bytes) console.log(new TextDecoder().decode(bytes));
console.log(vm.shares.get("host").list("/output"));

get() returns null for a file that isn't there, and list() marks directories with a trailing /.

Snapshots

A share's tree is part of the machine's state: savevm and migrate save it, and restoring brings it back.

See also

• WEMUShare
• Disks and images