Re: [PATCH 0/3] clone64() and unshare64() system calls

[Cedric Le Goater <clg@fr.ibm.com>]

H. Peter Anvin wrote:
> sukadev@us.ibm.com wrote:
>> This is a resend of the patch set Cedric had sent earlier. I ported
>> the patch set to 2.6.25-rc8-mm1 and tested on x86 and x86_64.
>> ---
>>
>> We have run out of the 32 bits in clone_flags !
>>
>> This patchset introduces 2 new system calls which support 64bit
>> clone-flags.
>>
>>      long sys_clone64(unsigned long flags_high, unsigned long flags_low,
>>         unsigned long newsp);
>>
>>      long sys_unshare64(unsigned long flags_high, unsigned long
>> flags_low);
>>
>> The current version of clone64() does not support CLONE_PARENT_SETTID
>> and CLONE_CHILD_CLEARTID because we would exceed the 6 registers limit
>> of some arches. It's possible to get around this limitation but we
>> might not
>> need it as we already have clone()
>>
> 
> I really dislike this interface.
> 
> If you're going to make it a 64-bit pass it in as a 64-bit number,
> instead of breaking it into two numbers.  Better yet, IMO, would be to
> pass a pointer to a structure like:
> 
> struct shared {
>     unsigned long nwords;
>     unsigned long flags[];
> };
> 
> ... which can be expanded indefinitely.

ok.

What about the copy_from_user() overhead ? is this something we care 
about for a clone like syscall ?

If not, this would certainly make our life simpler to extend clone flags.
I'm ready to implement anything if someone would just tell me in which
direction.

Thanks !

C.