lkml.org 
[lkml]   [2013]   [Nov]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 02/14] sched: add extended scheduling interface. (new ABI)
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.



\
 
 \ /
  Last update: 2013-11-27 14:41    [W:0.472 / U:0.664 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site