making a qdev bus available from a (non-qtree?) device

[Klaus Jensen]

Hi all,






  -device nvme,id=nvme-ctrl-0,serial=foo,...
  -device nvme-ns,id=nvme-ns-0,bus=nvme-ctrl-0,...
  -device nvme-ns,id-nvme-ns-1,bus=nvme-ctrl-0,...



  bus: main-system-bus
  type System
    ...
    dev: q35-pcihost, id ""
      ..
      bus: pcie.0
        type PCIE
        ..
        dev: nvme, id "nvme-ctrl-0"
          ..
          bus: nvme-ctrl-0
            type nvme-bus
            dev: nvme-ns, id "nvme-ns-0"
              ..
            dev: nvme-ns, id "nvme-ns-1"
              ..


Nice and qdevy.





  -device nvme-subsys,id=nvme-subsys-0,...
  -device nvme-ns,bus=nvme-subsys-0



  -device nvme-subsys,id=nvme-subsys-0,...
  -device nvme,id=nvme-ctrl-0,subsys=nvme-subsys-0
  -device nvme-ns,bus=nvme-ctrl-0




Thanks,
Klaus

I need some help with grok'ing qdev busses. Stefan, Michael - David suggested on IRC that I CC'ed you guys since you might have solved a similar issue with virtio devices. I've tried to study how that works, but I'm not exactly sure how to apply it to the issue I'm having. Currently, to support multiple namespaces on the emulated nvme device, one can do something like this: The nvme device creates an 'nvme-bus' and the nvme-ns devices has dc->bus_type = TYPE_NVME_BUS. This all works very well and provides a nice overview in `info qtree`: We have since introduced support for NVM Subsystems through an nvme-subsys device. The nvme-subsys device is just a TYPE_DEVICE and does not show in `info qtree` (I wonder if this should actually just have been an -object?). Anyway. The nvme device has a 'subsys' link parameter and we use this to manage the namespaces across the subsystem that may contain several nvme devices (controllers). The problem is that this doesnt work too well with unplugging since if the nvme device is `device_del`'ed, the nvme-ns devices on the nvme-bus are unrealized which is not what we want. We really want the namespaces to linger, preferably on an nvme-bus of the nvme-subsys device so they can be attached to other nvme devices that may show up (or already exist) in the subsystem. The core problem I'm having is that I can't seem to create an nvme-bus from the nvme-subsys device and make it available to the nvme-ns device on the command line: The above results in 'No 'nvme-bus' bus found for device 'nvme-ns', even though I do `qbus_create_inplace()` just like the nvme device. However, I *can* reparent the nvme-ns device in its realize() method, so if I instead define it like so: I can then call `qdev_set_parent_bus()` and set the parent bus to the bus creates in the nvme-subsys device. This solves the problem since the namespaces are not "garbage collected" when the nvme device is removed, but it just feels wrong you know? Also, if possible, I'd of course really like to retain the nice entries in `info qtree`.

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