Re: [9fans] Solo factotum (was: Enterable namespaces: /proc/pid/$ns/srv)

["David Arroyo" <david@arroyo.cc>]

On Mon, Dec 29, 2025, at 09:40, sirjofri via 9fans wrote:
> I don't know much about USB, though maybe the nusb/serial restriction
> only applies for real rxtx serial converters or something? I mean, USB
> is serial by its nature so any communication is serial, I guess...

My limited understanding is that the device & interface class is a hint
to the host as to how it should be interacted with.

https://www.usb.org/defined-class-codes

On 9front, it tells nusbrc which user-level driver to execute. On Linux,
it would tell the kernel whether to expose the device as a block device,
or a serial device, or a file system, etc. The device class 0x0A,
CDC-Data, seems like the closest thing to a pipe. I could always, of
course, define a new device class if there is a mismatch of expectations.

> However, being able to mount 9p from a USB serial line would be
> interesting for many use cases.

Yes. Imagine a "driverless" USB network adapter, which serves an ether(3)
file system using 9P over USB. Or an audio card, or mouse, or ...

> For the factotum key, another complex issue could be that factotum
> needs access to the network interface for auth stuff. I was thinking
> about this, and plan 9 makes it possible to solve this. One could for
> example put the /net of the host into a /srv of the factotum key,
> or something like that. In any case, this is a challenge to find a
> good and clean solution.

I had not thought about that. I will probably start with the protocols
which can be completed offline, such as ssh. For protocols which need
the auth server to validate the peer's key, I'm not sure. Perhaps the
needkey interface can be used to supply information that could be used
to validate the peer's credentials.

David

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