Re: [PATCH] powerpc: Enable demuxed sysv IPC syscalls

["Paul E. Murphy" <murphyp at linux dot vnet dot ibm dot com>]

On 12/15/2015 03:46 PM, Arnd Bergmann wrote:
> On Tuesday 15 December 2015 15:20:14 Paul E. Murphy wrote:
>>
>> Would a respin removing shmctl, semctl, and msgctl be acceptable?
>>
>> I'd argue switching to the demuxed version is still better than going
>> through the mux. At worst this superfluously sets the IPC64 bit for
>> kernel's which assume it. Is it even possible to change the behavior
>> of these syscalls now?
> 
> They have not yet been part of a released kernel, so I think it's still
> possible to change or remove them before 4.4 comes out. If we get the
> 4.4 release with the syscalls in place, we should not change the behavior
> any more, otherwise life gets too confusing in user space.
> 
> Similarly, I'd argue that removing just those three syscalls but leaving
> the other ones in place would only make it harder to use them correctly
> later, because every libc that wants to use them has to not only check
> if the separate calls are available at all, but also whether the
> three *ctl calls need special treatment.
> 

So, the bug is that some kernels check for, and clear the IPC64 bit, and
some assume it, but don't clear it? I guess that can't be checked at
compile time.

Isn't that still an issue with the current implementations? I guess
IA64 gets around it by generating these syscalls code dynamically.