usb_msd_init() calls qemu_opts_create() with a made-up ID and false
fail_if_exists. If the ID already exists, it happily messes up those
options, then fails drive_new(), because the BlockDriverState with
that ID already exists, too.
Reproducer: -drive if=none,id=usb0,format=raw -usbdevice disk:tmp.qcow2
Pass true fail_if_exists to qemu_opts_create(), and if it fails, try
the next made-up ID.
The reproducer now succeeds, and creates an usb-storage device with ID
usb1.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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