nvme/pcie hot plug results in /dev name change

[Keith Busch]

On Fri, Jan 20, 2023 at 02:50:46PM -0500, John Meneghini wrote:
> We have a customer complaining that when they hot unplug/plug their nvme-pci device the device name changes.
> 
> For example, when they hot remove /dev/nvme1n1 physically, then reinsert it, it gets identified as /dev/nvme4n1.
> 
> IIRC there is nothing about nvme_init_ctrl that guarantees the ctrl->instance will be the same because
> ida_alloc() will only return the next free id in the bitmap.
> 
> The fact that nvme_remove ->  nvme_init_ctrl many times results in the same
> ctrl->instance is just a happen stance and there is nothing that guarantees
> /dev name consistency in Linux. Especially in the case of hot unplug/plug
> where the controller may very well be marked NVME_CTRL_DEAD due to the
> ungraceful disconnect.

That is correct. We don't know the identity of the device at the point
we have to assign it an instance number, so the hot added one will just
get the first available unique number. If you need a consistent name, we
have the persistent naming rules that should create those links in
/dev/disk/by-id/.