zvol_dumpio would be cleaner with vdev_op_dumpio
Review Request #2480 - Created Jan. 7, 2020 and submitted
There is currently unnecessary leakage of vdev internals into the zvol code. This change removes those leakages and keeps the relevant code with the rest of the vdev code (which also simplifies some upcoming fixes).
Notes in ticket -- tl;dr forced panics with dump devices on a zpool with various configurations and verified resulting dump could be read and loaded in mdb after the panic.