Add support for sharing host directories into the VM via QEMU 9p
(virtio-9p). The --mount flag can be repeated; each host directory
appears at the same absolute path inside the VM.
Design:
- QEMU: each --mount gets a short 9p tag (slim0, slim1, …) via
-virtfs local,path=…,mount_tag=slimN,security_model=mapped-xattr.
Tags are kept short because 9p mount_tag has a ~31-byte limit.
- Kernel cmdline: the full destination path is passed as
slim.mount=<tag>:<base64(path)> so the init script knows where to
mount each tag. Base64 avoids issues with spaces/special chars.
- slim-init.sh: after networking, parse slim.mount= entries, mkdir -p
the destination, and mount -t 9p <tag> <dest> -o trans=virtio,version=9p2000.L
Tests verify: 9p share detection via sysfs mount_tag, 9p entry in
mount output, file content accessible at the expected path, and clean
VM exit.
marvin
90de50dfed