Re: [PATCH 0/3] net/9p: Add 9P transport over USB4STREAM

[Dominique Martinet <asmadeus@codewreck.org>]

Mika Westerberg wrote on Mon, Nov 09, 2026 at 05:52:36PM +0100:
> > In case of one-shot backup, I think my drag&drop scenario from cover-
> > letter fits it well. Assuming single thread copy, both transports
> > achieve similar results, but with busy-poll enabled, trans=thunderbolt
> > cuts about 1/3rd of copy time:
> > Copy from 9P client to a server, using trans=fd, takes 22m29s while
> > trans=thunderbolt + busy-poll takes 14m50s (~1.5x faster).
> > Reverse direction, same improvement: reducing copy time from 41m07s to
> > 26m56s. All done on default msize.
> 
> That sounds like a good reason to include it IMHO. Also I like the
> simplicity - no need to run a separate descriptor feeding process :)

I'm sorry but I'm just not convinced it's useful enough to warrant the
effort to review this from my point of view given my lack of time for
linux work:
- most of the speed benefit comes from busy-poll, can't this be made to
work for all fd consumers somehow? (it could be an ioctl before passing
the fd to the mount call, or it could reuse e.g. the existing NAPI
config with network over usb4stream if that's more practical; in
particular I recall some drivers supporting a hybrid mode that'd
busy-poll for x ns/ms then fall back to waiting for the irq, that'd get
you the best of both worlds as a sane default)
- for simplicity it looks like mounting from boot without initrd isn't a
goal, so this can all be hidden in a userspace wrapper. 9p has
historically always been pretty bare, we're not even doing dns
resolution that has been a basic feature available for nfs since
forever.
You can look at this mount.9P helper for inspiration:
https://github.com/nfs-ganesha/nfs-ganesha/blob/V15.2/src/tools/mount.9P

> > I would be happy to maintain Thunderbolt transport.
> 
> If Dominique is okay with this, I suggest to send v2 with a MAINTAINERS
> update as well.

OTOH if you're going to maintain this I have no reason to block, I can
just say I'm not reviewing in depth and pass the ball to Linus or
someone else higher up the stack to decide...

-- 
Dominique Martinet | Asmadeus