linux-kernel - Re: usbip doesn't work with userspace code that accesses USB devices

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Date: Tue, 5 Mar 2024 13:03:40 -0500
From: Demi Marie Obenour <demi@...isiblethingslab.com>
To: Alan Stern <stern@...land.harvard.edu>,
	Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
Cc: Greg KH <gregkh@...uxfoundation.org>, linux-usb@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: usbip doesn't work with userspace code that accesses USB devices

On Mon, Mar 04, 2024 at 10:19:24PM -0500, Alan Stern wrote:
> On Tue, Mar 05, 2024 at 12:52:22AM +0100, Marek Marczykowski-Górecki wrote:
> > On Mon, Mar 04, 2024 at 11:46:04PM +0100, Marek Marczykowski-Górecki wrote:
> > > Terminology:
> > > 1. sys-usb - a VM where USB controller (a PCI device) lives; here
> > > usbip-host is attached to the device
> > > 2. testvm - target VM where usbip is connected; here vhci-hcd is used
> > > 3. qvm-usb - tool that connects the above two (equivalent of
> > > userspace part of standard usbip)
> > > 
> > > Specific steps:
> > > 1. Connect android phone - at this point it's only in sys-usb
> > > 2. Switch its mode to file transfer - observe reconnect in sys-usb
> > > 3. Use qvm-usb to attach it to the testvm
> > > 4. Call jmtpfs -d /mnt in testvm
> > 
> > Or maybe reset or something is involved here too?
> > 
> > After using qvm-usb to attach _and detach_ the device, it stays bound to
> > usbip-host driver (that's intentional). But then, even after re-binding
> > back to the "usb" driver, jmtpfs called in sys-usb directly fails the
> > same way, including failure to reset.
> > 
> > In fact, even without usbip involved at all, jmtpfs directly in sys-usb
> > works only once. The second attempt (without either physically reconnecting
> > the phone, or changing its more to "no data transfer" and back to "file
> > transfer") fails the same way. After terminating the first instance, I
> > see just this logged:
> > 
> >     [921332.525210] usb 2-1: reset high-speed USB device number 22 using xhci_hcd
> 
> If something doesn't work when usbip isn't involved, you definitely 
> shouldn't expect it to work when usbip _is_ involved.

With usbip, jmtpfs fails the _first_ time, instead of only the _second_
time.  This might be related: maybe the attachment of usbip acts like
the first attach?
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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