Ensure major/minor number combinations are never reused

[DemiMarie]

To avoid race conditions in userspace, major/minor device combinations for hot-pluggable devices should never be reused.

[kees]

Doesn't this pose a denial of service risk once the device number range is exhausted?

[DemiMarie]

The full range (major + minor) is 64 bits, so I don’t think we need to worry about it running out. That said, an even nicer approach would be to use something other than major and minor numbers to identify a device. Perhaps have a /dev/disk/by-diskseq filesystem maintained in the kernel, and something similar for character devices?