Revocable references vs. krefs

Posted Sep 29, 2025 9:10 UTC (Mon) by farnz (subscriber, #17727)
In reply to: Revocable references vs. krefs by Alan.Stern
Parent article: Revocable references for transient devices

The use case is where you have something claiming a removable device, like a PPP driver (for example); in other words, where the subsystem registers with the removable device, rather than the normal way round.

You want the subsystem to stop doing work that depends on the removable device being present as quickly as possible - there is no point spending lots of compute on building a new PPP frame to send, or a new work item to pass across to the GPU, if the underlying hardware is gone. Instead, you want it to error out early and stop wasting time doing things that it's going to submit to a driver that's already deregistered from the subsystem.

Revocable references vs. krefs

Posted Sep 29, 2025 13:55 UTC (Mon) by Alan.Stern (subscriber, #12437) [Link] (1 responses)

Okay, that makes sense. Jon's original article did not draw any distinction between a subsystem claiming a removable device and the device's driver registering with a subsystem.

Revocable references vs. krefs

Posted Sep 30, 2025 0:50 UTC (Tue) by riking (subscriber, #95706) [Link]

Of course, for the subsystems that the removable device's driver does register with, it *cannot* process those unregistrations until it is satisfied that its consumers have stopped trying to use the device (now, via struct revokable). Once the SRCU critical section has passed, the subsystem deregistrations can happen.