Gerd Hoffmann <kra...@redhat.com> writes: > Hi, > > Peter Maydell <peter.mayd...@linaro.org> writes: > >> If you have a model with more than one USB bus, and you >> create a USB device on the command line without specifying >> which bus to plug it into, QEMU will choose a different bus >> depending on whether you use the legacy "-usbdevice keyboard" >> or the qdev "-device usb-kbd". >> >> This is because the legacy option finds the USB bus with >> usb_bus_find(), which searches the 'busses' list, which is >> populated by usb_bus_new(), with each new bus added to the >> tail of the list. The qdev option looks for the USB bus >> with qbus_find_recursive(), which walks the qdev tree. >> Since qbus_create_inplace() adds each new child bus to >> the front of the parent's child_bus list, this means that >> qbus_find_recursive() will encounter the last-added bus >> first, whereas usb_bus_find() will get the first-added bus.
The fact that we duplicate qtree information in a separate list "busses" either means we've been too lazy to garbage collect busses, or we've failed to make working with the qtree as easy as it should be. > Quite a while back I've tried to switch qdev from QLIST to QTAILQ > exactly to allow adding stuff to the tail of the lists(s), because > that feels more natural to me than the current ordering. "info qtree" > is upside-down too ;) Has always annoyed me. Let's bite the bullet and change it. > Gave up after resending it one or two times, the forgot about it, > wasn't *that* important to me. Still got a pointer to the patch? qdev is too important to continue much longer without a maintainer. >> I assume this is likely to apply to other bus types as well. >> >> Is there anything we can do to fix this inconsistency [*], >> or are we tied to the existing enumeration orders in both >> cases for compatibility with users with currently-working >> command lines or configurations? > > Could be we break something. I think it is unlikely though. Multiple > busses of the same type are pretty uncommon, and any examples with > multiple lsi adapters (for example) advertise explicitly assign > devices via bus=. libvirt uses bus= everywhere too. The sooner we fix up the order, the less stuff we'll break. >> [*] the actual code changes are simple enough, obviously Care to cook up a patch?
