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

[Daniel Mack <daniel-cYrQPVfZoowdnm+yROfE0A@public.gmane.org>]

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