Names

One device has several names, as on a real Linux system, where a disk is /dev/sda, and also /dev/disk/by-path/... and /dev/disk/by-id/....

Slot path

A part in the case’s connector has the connector’s path: eeprom, sata:0, exp:1. The path is the device’s address on the bus, as a position on real hardware is. A part moved to another connector has a new path.

Id

Every device has an id, id:<uuid>, that stays the same however it is connected: in a slot, on a cable, behind a hub. A part that has been in a computer carries its id on its item. Crafting it alone makes it a new device and clears the id. External devices are addressed by their id.

Virtual names

The motherboard provides devices that always exist. console is the one you meet: the board’s console, which merges every terminal on the bus into one. Writing to it writes to all of them, and reading from it reads the keys typed at any of them. Its name is fixed.

mcos names

mcos names a device by its type and its place among devices of that type in bus order: terminal0, storage0, storage1, redstone0. The EEPROM is just eeprom, and the first sound card is dsp, then dsp1, as OSS names them. These are the names under /dev (see /dev), and lsdev lists them with each one’s slot path and, with -i, its id: see lsdev.

Inside, mcos keeps a device by its id: an open file holds an id, so if a part is moved, or another device takes its name, the file still reaches the same device or fails; it never reaches another one by accident.

Why names meet in one place

Everything the host keeps for a program about a device (what it waits for, the streams it reads, its rings) is kept by the name the program used for it. Interrupts come from the bus by address, and each one is turned into the program’s name before anything compares it. Comparing names as strings in many places once let a card in a slot fail to wake a computer that waited for it by its id; now there is one place that does it.