blockdev.c will create implicit virtio-blk-* devices for IF_VIRTIO drives. I want to turn this on for the ARM virt board (now it has PCI), so that users can use shorter and more comprehensible command lines.
Unfortunately, the code as it stands will always create an implicit device, which means that setting the virt block_default_type to IF_VIRTIO would break existing command lines like: -drive file=arm-wheezy.qcow2,id=foo -device virtio-blk-pci,drive=foo because the creation of the drive causes us to create an implied virtio-blk-pci which steals the drive, and then the explicit device creation fails because 'foo' is already in use. This patchset fixes this problem by deferring the creation of the implicit devices to drive_check_orphaned(), which means we can do it only for the drives which haven't been explicitly connected to a device by the user. The slight downside of deferral is that it is effectively rearranging the order in which the devices are created, which means they will end up in different PCI slots, etc. We can get away with this for PCI, because at the moment the only machines which set their block_default_type to IF_VIRTIO are the S390X ones. I have special-cased S390X to retain the old behaviour, which is a bit ugly but functional. If S390X doesn't care about cross-version migration we can probably drop that and just have everything defer. S390X people? The code in master didn't seem to take much account of the possibility of hotplug -- if the user created a drive via the monitor we would apparently try to create the implicit drive, but in fact not do so because vl.c had already done device creation long before. I've included a patch that makes it more explicit that hotplug does not get you the magic implicit devices. The last patch is the oneliner to enable the default for virt once the underlying stuff lets us do this without breaking existing user command lines. Peter Maydell (4): blockdev: Factor out create_implicit_virtio_device blockdev: Don't call create_implicit_virtio_device() when it has no effect blockdev: Defer creation of implicit PCI devices for IF_VIRTIO drives hw/arm/virt: Make block devices default to virtio blockdev.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++------------ hw/arm/virt.c | 1 + 2 files changed, 59 insertions(+), 14 deletions(-) -- 1.9.1