On Tue, Feb 25, 2025 at 08:49:16PM -0400, Jason Gunthorpe wrote: > I'm pointing out the fundamental different in approachs. The typical > widely used pattern results in __device_release_driver() completing > with no concurrent driver code running. Typically yes, but there are exceptions, such as DRM. > > DRM achieves this, in part, by using drm_dev_unplug(). No, DRM can have concurrent driver code running, which is why drm_dev_enter() returns whether the device is unplugged already, such that subsequent operations, (e.g. I/O) can be omitted. > > The Rust approach ends up with __device_release_driver() completing > and leaving driver code still running in other threads. No, this has nothing to do with Rust device / driver or I/O abstractions. It entirely depends on the driver you implement. If you register a DRM device, then yes, there may be concurrent driver code running after __device_release_driver() completes. But this is specific to the DRM implementation, *not* to Rust. Again, the reason a pci::Bar needs to be revocable in Rust is that we can't have the driver potentially keep the pci::Bar alive (or even access it) after the device is unbound. A driver can also be unbound without the module being removed, and if the driver would be able to keep the pci::Bar alive, it would mean that the resource region is not freed and the MMIO mapping is not unmapped, because the resource region and the MMIO mapping is bound to the lifetime of the pci::Bar object. This would not be acceptable for a Rust driver. That this also comes in handy for subsystems like DRM, where we could have attempts to access to the pci::Bar object after the device is unbound by design, can be seen as a nice side effect.
