QEMU 5.1 no longer says anything about inaccessible devices

[Diego Viola]

Previously, with QEMU 5.0.0 running a VM with the following command:

$ qemu-system-x86_64 -enable-kvm -hda arch-zoom.qcow2 -m 4G -device usb-ehci,id=ehci -device usb-host,bus=ehci.0,vendorid=0x04f2,productid=0xb449 -device intel-hda -device hda-duplex -vga virtio

Would display something like the following:

libusb: error [_get_usbfs_fd] libusb couldn't open USB device /dev/bus/usb/002/004: Permission denied
libusb: error [_get_usbfs_fd] libusb requires write access to USB device nodes.
libusb: error [_get_usbfs_fd] libusb couldn't open USB device /dev/bus/usb/002/004: Permission denied
libusb: error [_get_usbfs_fd] libusb requires write access to USB device nodes.

With insufficient permissions.

QEMU 5.1.0 no longer displays anything.

I did a git bisect and this is the result:

[diego@thinkpad qemu]$ git bisect bad
9f815e83e983d247a3cd67579d2d9c1765adc644 is the first bad commit
commit 9f815e83e983d247a3cd67579d2d9c1765adc644
Author: Gerd Hoffmann <email address hidden>
Date: Fri Jun 5 14:59:52 2020 +0200

    usb: add hostdevice property to usb-host

    The new property allows to specify usb host device name. Uses standard
    qemu_open(), so both file system path (/dev/bus/usb/$bus/$dev on linux)
    and file descriptor passing can be used.

    Requires libusb 1.0.23 or newer. The hostdevice property is only
    present in case qemu is compiled against a new enough library version,
    so the presence of the property can be used for feature detection.

    Signed-off-by: Gerd Hoffmann <email address hidden>
    Message-Id: <email address hidden>

 hw/usb/host-libusb.c | 75 ++++++++++++++++++++++++++++++++++++++++++----------
 hw/usb/trace-events | 1 +
 2 files changed, 62 insertions(+), 14 deletions(-)
[diego@thinkpad qemu]$

[Diego Viola (diego-viola-deactivatedaccount)]

The previous commit is fine, it displays the USB errors:

libusb: error [_get_usbfs_fd] libusb couldn't open USB device /dev/bus/usb/002/004: Permission denied
libusb: error [_get_usbfs_fd] libusb requires write access to USB device nodes.
libusb: error [_get_usbfs_fd] libusb couldn't open USB device /dev/bus/usb/002/004: Permission denied
libusb: error [_get_usbfs_fd] libusb requires write access to USB device nodes.

[Diego Viola (diego-viola-deactivatedaccount)]

My system is Arch Linux.

[Diego Viola (diego-viola-deactivatedaccount)]

Not sure this is a bug.

[Diego Viola (diego-viola-deactivatedaccount)]

I was changing the /dev file permissions based on the output from above, that's why I decided to submit this bug report.

Either way, the output from lsusb works too.

[Diego Viola (diego-viola-deactivatedaccount)]

I no longer need this (it's no longer an issue for me), feel free to reopen if this issue affects you.