allocate an official device major number for virtio device?

[Jin Qian]

Hi -

Can we allocate an official device major number for virtio devices?
Currently it's using 240-254 (LOCAL/EXPERIMENTAL USE). The reason we
ask for this is because userspace will need to treat virtio block
devices differently and need a way to detect such device. For example,
it checks major number to detect scsi and mmc device.

https://android-review.googlesource.com/#/c/195240

With dynamic major numbers 240-254, we might treat other devices as
virtio block device incorrectly.

Also open for suggestions on what's the correct way to handle this.

Thanks in advance!
jin