Re: [PATCH 01/13] kdbus: add documentation

On 01/20/2015 02:53 PM, Michael Kerrisk (man-pages) wrote:

This is an enormous and complex API. Why is the API ioctl() based,
rather than system-call-based? Have we learned nothing from the hydra
that the futex() multiplexing syscall became? (And kdbus is an order
of magnitude more complex, by the look of things.) At the very least,
a *good* justification of why the API is ioctl()-based should be part
of this documentation file.

I think the simplest reason is because we want to be able to build kdbus
as a module. It's rather an optional driver than a core kernel feature.
IMO, kernel primitives should be syscalls, but kdbus is not a primitive
but an elaborate subsystem.

Also, the context the kdbus commands operate on originate from a
mountable special-purpose file system. Hence, we decided not to use a
global kernel interface but specific ioctls on the nodes exposed by kdbusfs.


Thanks,
Daniel