
qemu usb storage emulation
--------------------------

QEMU has three devices for usb storage emulation.

Number one emulates the classic bulk-only transport protocol which is
used by 99% of the usb sticks on the market today and is called
"usb-storage".  Usage (hooking up to xhci, other host controllers work
too):

  qemu ${other_vm_args}                                \
       -drive if=none,id=stick,file=/path/to/file.img  \
       -device nec-usb-xhci,id=xhci                    \
       -device usb-storage,bus=xhci.0,drive=stick


Number two is the newer usb attached scsi transport.  This one doesn't
automagically create a scsi disk, so you have to explicitly attach one
manually.  Multiple logical units are supported.  Here is an example
with tree logical units:

  qemu ${other_vm_args}                                                \
       -drive if=none,id=uas-disk1,file=/path/to/file1.img             \
       -drive if=none,id=uas-disk2,file=/path/to/file2.img             \
       -drive if=none,id=uas-cdrom,media=cdrom,file=/path/to/image.iso \
       -device nec-usb-xhci,id=xhci                                    \
       -device usb-uas,id=uas,bus=xhci.0                               \
       -device scsi-hd,bus=uas.0,scsi-id=0,lun=0,drive=uas-disk1       \
       -device scsi-hd,bus=uas.0,scsi-id=0,lun=1,drive=uas-disk2       \
       -device scsi-cd,bus=uas.0,scsi-id=0,lun=5,drive=uas-cdrom


Number three emulates the classic bulk-only transport protocol too.
It's called "usb-bot".  It shares most code with "usb-storage", and
the guest will not be able to see the difference.  The qemu command
line interface is simliar to usb-uas though, i.e. no automatic scsi
disk creation.  It also features support for up to 16 LUNs.  The LUN
numbers must be continuous, i.e. for three devices you must use 0+1+2.
The 0+1+5 numbering from the "usb-uas" example isn't going to work
with "usb-bot".

enjoy,
  Gerd

--
Gerd Hoffmann <kraxel@redhat.com>
