How to obtain a protocol interface

[scholzp]

Hi all,
in my current use case I try to obtain a protocol interface pointer, not for the purpose of using it, but rather to uninstall the protocol from an handle. This is necessary as one is required to call Bootservices::uninstall_protocol_interface. Normally for such functionality I would use EFI_BOOT_SERVICES.HandleProtocol() (see spec 7.3.7), which would return the interface pointer. This function is not implemented in the crate and Bootservices::test_protocol, which would conceptually achieve the same result as HandleProtocol, doesn't return a pointer to the interface either.

For me the only possible way to do this seems to be by using open_protocol, dereferenceing the ScopedProtocol, somehow create a pointer from it and then use this to uninstall the protocol, after I closed it of course. This feels a bit hacky to me and I would prefer a more intuitive way for obtaining an interface pointer. Is there any better way to do this, of which I'm unaware? If not, would you be interested in such a feature?

Thanks for your help!

[nicholasbishop]

I had to ponder this a bit :) It is possible to do with the current API, and I've put up a PR to demonstrate this in the test-runner: #931

It's not exactly the most intuitive thing though, so I'm open to suggestions on improving this. I expect uninstalling a protocol interface to be relatively uncommon though, so maybe it's OK for it to be a little clunky -- I'm unsure.

[scholzp]

Hi Nicholas, thank you for your response and the example! :)

I think the way you demonstrated this is the way, it should be done when using the crate. I've implemented a handle_protocol wrapper in the meantime and didn't find a way to really integrate it in a useful way into this crate. It would introduces a lot of unsafety in my option when handling protocols, as the handler isn't automatically registered by the UEFI as it would be the case when using open_protocol. So it might be better if there only exists one way of obtaining a interface pointer. I too think, that uninstalling a protocol interface should be a uncommon task and in the seldom cases where it's useful, it's OK to be a bit clunky. But this is just my thoughts about this.

So again, thank you for your answer! :)