On Wed, Nov 27, 2013 at 02:23:54PM +0100, Ingo Molnar wrote: > There are 3 main compatibility cases: > > - the kernel's 'sizeof sched_attr' is equal to sched_attr:size: the > kernel version and user-space version matches, it's a straight ABI > in this case with full functionality. > > - the kernel's 'sizeof sched_attr' is larger than sched_attr::size > [the kernel is newer than what user-space was built for], in this > case the kernel assumes that all remaining values are zero and acts > accordingly.
It also needs to fail sched_getparam() when any of the fields that do not fit in the smaller struct provided are !0. > - the kernel's 'sizeof sched_attr' is smaller than sched_attr::size > [the kernel is older than what user-space was built for]. In this > case the kernel should return -ENOSYS if any of the additional > fields are nonzero. If those are all zero then it will work as if a > smaller structure was passed in. So the problem I see with this one is that because you're allowed to call sched_setparam() or whatever it will be called next on another task; a task can very easily fail its sched_getparam() call. Suppose the application is 'old' and only supports a subset of the fields; but its wants to get, modify and set its params. This will work as long nothing will set anything it doesn't know about. As soon as some external entity -- say a sysad using schedtool -- sets a param field it doesn't support the get, modify, set routing completely fails. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
