The files machine

A USB stick's filesystem is whatever its last owner put on it, and the kernel's filesystem code is some of its most attacked. On a PC, drives and SD cards are mounted in sys-files, a machine of their own, and only their files cross to the host. sys-files has no network card at all, so nothing on a drive can reach anything but the host.

Like the network machine, sys-files is BusyBox, one program (losos-filesd) and the host's own kernel, hidden from the Machines app.

How a drive gets there

• A USB drive is moved there by the peripherals router, over USB/IP. The router starts sys-files if it is not running.
• An SD card reader on the PCI bus is handed to sys-files at boot, and sys-files starts at boot to hold it.

losos-filesd mounts each filesystem it recognises: FAT, exFAT, NTFS, ext2 to ext4, Btrfs, XFS, F2FS, and CD and DVD formats. Nothing on a drive can run, and nothing on it can be a device. It leaves other things alone, such as swap or an encrypted volume.

In Files

On the host, losos-files-host mounts each volume for the person whose session is in front, under /run/media/<user>/<name>. It uses sshfs, with OpenSSH's sftp-server in the machine at the other end of a losos-vm-call connection. The name is the volume's label. The files show as the person's own, and the kernel checks access as it would for their own files.

losos-files eject <name> unmounts a volume and tells the kernel the drive is going, so it can be pulled out. losos-files list lists what is mounted.

Lazy

sys-files powers itself off five minutes after the last drive goes, and gives its memory back to the host while it runs. The next drive starts it again.

Network shares

SMB, NFS and WebDAV shares are mounted in a second machine, sys-shares, which is sys-files with a network card. That card is on the host's link to the network machine, which routes it as it routes the host: through the ad blocker's DNS, and through Tor in schizo mode. sys-shares keeps the shares and their passwords on a small disk of its own, which only it reads. The host only remembers that shares were added, so it can start sys-shares at boot.

printf '%s\n%s\n' "$user" "$password" | losos-shares add Photos smb://nas/photos
losos-shares list
losos-shares remove Photos

The shares appear under /run/media/<user>/<name> like drives.

Backups to a LosOS box do not use sys-shares. They talk HTTPS to the box through the LosOS boxes machine and check the box's certificate on every connection.

The pieces

Piece	Where
The files machine and its host half	nixos/modules/files-machine.nix, losos-files-host.sh
The network shares machine	nixos/modules/shares-machine.nix
The machines' program	src/losos-filesd