[Bug 1843711] Re: qemu-xhci device should detect if libusb host supports streams

[Thomas Huth]

The QEMU project is currently considering to move its bug tracking to
another system. For this we need to know which bugs are still valid
and which could be closed already. Thus we are setting older bugs to
"Incomplete" now.

If you still think this bug report here is valid, then please switch
the state back to "New" within the next 60 days, otherwise this report
will be marked as "Expired". Or please mark it as "Fix Released" if
the problem has been solved with a newer version of QEMU already.

Thank you and sorry for the inconvenience.


** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1843711

Title:
  qemu-xhci device should detect if libusb host supports streams

Status in QEMU:
  Incomplete

Bug description:
  When using USB passthrough with the qemu-xhci (and nec-usb-xhci),
  streams are enabled by default, but if the host xHCI controller
  doesn't support them, it will trigger hard-to-debug UAS guest errors.

  This should be possible to detect since the kernel returns ENOSYS (errno 38) 
when xhci host controller does not support streams:
              libusb: error [do_streams_ioctl] streams-ioctl failed error -1 
errno 38
              qemu: libusb_alloc_streams: -99 [OTHER]

  Maybe libusb should return a dedicated error instead of
  LIBUSB_ERROR_OTHER in this case, but qemu does not handle any other
  error code anyway.

  Just trying to enable streams before enabling them in qemu should do
  it. I don't know if it should be done in hcd-xhci.c, host-libusb.c or
  elsewhere, but this would be detectable at launch instead of a static
  option true/false, maybe a ternary with auto would be better.

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