Re: [Qemu-devel] [patch] USB support

[Fabrice Bellard <fabrice@bellard.org>]

> When I use usb_add, I get:
> USBDEVFS_DISCONNECT: Inappropriate ioctl for device
> 
> This is with snapshot from 2005-11-11, on Debian testing, kernel 2.6.13
> (with 1000Hz timer).
> The patch below fixes this (plainly taken from
> http://www.mail-archive.com/linux-usb-devel@lists.sourceforge.net/msg35550.html
> ; is ifno = 0 correct?)

Thank you. I was not able to test this ioctl on my PC, hence the problem...

> With this patch, qemu recognized all USB devices I had available - which
> is actually only one device, a joystick :)
> Win2k showed it in the control panel with all available buttons and axes
> and reacted to events correctly.
> 
> Though, a strange thing is that as long as the device is attached to the
> guest, Windows gets very slow. The Windows task manager shows that the
> guest CPU load is at 100%; but "top" on the guest shows that qemu uses
> only 20% host CPU. This starts as soon as usb_add is executed, and stops
> as soon as usb_del is executed.
> Does qemu use sleep in the usb code, or does maybe Windows sent the CPU
> a HLT ? I don't really understand that behaviour :)

As mentionned in the documentation, the USB host emulation is very slow 
in QEMU. The problem is that USB requests block the whole VM. I plan to 
implement non blocking USB I/Os soon.

Fabrice.