Re: usb_keyboard not available as a terminal input?

[Tom Yan]

I did some follow-up tests with qemu/ovmf. The main command was still: 

qemu-system-x86_64 -enable-kvm -drive file=grub.img -drive 
if=pflash,readonly,file=ovmf_x64.bin

with these in addition, respectively:

1.  -device usb-ehci -device usb-kbd
2.  -device nec-usb-xhci -device usb-kbd

Here are the results:

1. on usb-ehci, with `nativedisk` I would lose keyboard control
2. on usb-ehci, with `nativedisk; insmod usb_keyboard` I could get a 
"usb_keyboard0" input terminal and keyboard control
3. on nec-usb-xhci, with `nativedisk` I would not lose keyboard control
4. on nec-usb-xhci, with `nativedisk; insmod usb_keyboard` I could not get any 
usb_keyboard input terminal but would not lose keyboard control

I then start the VM without any USB host/device attached, ran `nativedisk` and 
then `lsmod`, I can see that o/u/ehci are all loaded automatically. I happened 
to notice that nativedisk can take a parameter as well, and I got one more 
result after that:

5. on usb-ehci, with `nativedisk pata` I would not lost keyboard control.

So I guess I can conclude, usb_keyboard input terminal does rely on a working 
usb host controller grub driver, and if the corresponding one is loaded, the 
user will lose control to the USB keyboard (before a manual `insmod 
usb_keyboard`), and if it is not loaded, USB keyboard control will remain 
intact through console and the UEFI driver.

I still don't understand why all disk access would (need to) be lost once _any_ 
of the so-called relevant module is loaded though, even when the disk is not 
attached to any of those kinds of hosts. For example, why can't virtio-blk/scsi 
drives at the very least remain "intact" just like the "XHCI keyboard"? But I 
guess that's a bit off from the original topic and I am not sure if I am 
interested in digging further on this anyway. So I'll just leave it *shrug*

Anyway, thanks again!

Regards,
Tom


From: Andrei Borzenkov <address@hidden>
Sent: Monday, May 22, 2017 11:38 AM
To: Tom Yan; address@hidden
Cc: Bjørn Forsman
Subject: Re: usb_keyboard not available as a terminal input?
    
21.05.2017 23:02, Tom Yan пишет:
> It seems like the "disappearance" of storage drives after `insmod ehci` is 
> not relevant to whether the drives are USB ones.
> 
> For example, if I start a virtual machine with this:
> qemu-system-x86_64 -enable-kvm -drive file=grub.img -drive 
> if=pflash,readonly,file=ovmf_x64.bin
> 
> And do this after grub started:
> `ls; insmod ehci; ls`
> 
> It will print only _one_ line with multiple storage drives:
> (hd0), (hd0, gpt1), (fd0), (fd1), (cd0)
> which indicates that _everything_ is gone after the insmod command. Same case 
> with ohci/uhci.
> 
> This seems like a bug to me.
> 

it works as designed. USB driver change hardware state, so we cannot
give control back to firmware. You need to use direct hardware access
drivers from this point on. "nativedisk" command handles disk access for
you.

This is still best effort. We hope that firmware won't try to access
hardware on its own, but we do not really know it nor control it.