(Thanks for the reviews... I'll get back to the kernel code details after double-checking if this can be done from userspace.) > > Besides, what's wrong with binding to devices that weren't switched > > into AOA mode? Would that just provoke a bunch of unnecessary error > > messages? It's not about devices that aren't switched into AOA mode... it's about devices that are switched into AOA mode for other reasons (connecting to other Android apps). I don't think a kernel driver like that exists today, but it could be added, or people could use libusb to talk to an AOA device. AOA is just a general mechanism to talk to an Android app for whatever you want, and the descriptors sent during mode switch clarify what app it's talking to (and thereby what protocol it is using... it could be mass storage or it could be something entirely different). But a device switched into AOA mode for whatever app will always use that same well-known VID/PID (18d1:2d00). So if I just add that VID/PID to the IDs bound by the usb-storage driver, it would also grab a device that was mode-switched by userspace to talk to a completely different app. I need some way to make sure it only grabs the intended device, and there's no good identifier for that other than comparing the dev path to what you originally mode switched. > > > + /* > > > + * Only interface 0 connects to the AOA app. Android devices that have > > > + * ADB enabled also export an interface 1. We don't want it. > > > + */ > > > + if (us->pusb_intf->cur_altsetting->desc.bInterfaceNumber != 0) > > > + return -ENODEV; > > > > Do you really need this test? What would go wrong if you don't do it? Yes, otherwise two separate usb-storage instances bind to the two interfaces. The second interface is meant for a special ADB debugging protocol and will not respond at all to USB mass storage packets, so eventually the first request to it times out and usb_stor_invoke_transport() will do a port reset to recover. That also kills the first interface asynchronously even though it was working fine. > > IMO the userspace approach would be better, unless you can provide a > > really compelling argument for why it won't suffice. Well... okay, let me think through that again. I just found the new_id sysfs API that I wasn't aware of before, maybe I could leverage that to bind this from userspace after doing the mode switch. But it looks like that only operates on whole devices... is there any way to force it to only bind one particular interface?
