Currently, this is mostly implementation driven - there is one bit reserved for the derivation level in the data structure that tracks it. It’s possible that IRQControl caps specifically have some space left that could be used for more levels, but it would make them a special case.
If we reserved 2 bits for the level, you’d hit the same problem somewhat later, though, and the argument at the time was that (very small) finiteness of derivation levels of these control caps has to be solved at user level anyway and it’s better to make you think of it immediately rather than when you’ve designed yourself into a corner. Maybe you do have a very good use case here, though, and we should rethink that argument (as we did for endpoint caps - their level of specialness is pretty messy, but we considered it worth the pain). I should probably leave that part to Kevin. Cheers, Gerwin > On 16.02.2017, at 03:20, Andrew Gacek <[email protected]> wrote: > > Based on the seL4 manual it sounds like IRQControl caps only support > one level of derivation. What is the reason for this restriction? We > encountered a case where we wanted to hand out an IRQControl for a > specific irq and then later revoke access, but we couldn't do it > because the IRQControl for a specific irq is already a derived > capability. > > -Andrew > > _______________________________________________ > Devel mailing list > [email protected] > https://sel4.systems/lists/listinfo/devel _______________________________________________ Devel mailing list [email protected] https://sel4.systems/lists/listinfo/devel
