Re: [PATCH 11/11][v15]: Document sys_eclone

[Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>]

Albert Cahalan wrote:
> On Mon, Jul 5, 2010 at 12:10 AM, H. Peter Anvin <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org> wrote:
>> On 07/04/2010 04:39 PM, Matt Helsley wrote:
>>>> 1. can you implement it for i386 (register starved) using eclone?
>>> That's a very good question. I'm going to punt on a direct answer for
>>> now. Instead,  I wonder if it's even worth enabling vfork through eclone.
>>> vfork is rarely used, is supported by the "old" clone syscall, and any
>>> old code adapted to use eclone for vfork would need significant
>>> changes because of vfork's specialness. (A consequence of the way vfork
>>> borrows page tables and must avoid clobbering parent's registers..)
>> vfork is its own system call for a reason.  We used to do it with
>> sys_clone, and it turned out to be a mess.  Doing it in a separate
>> system call -- even though the internals are largely the same -- is cleaner.
> 
> That's interesting; only ia64 and xtensa still do vfork via clone.
> I remember sys_vfork being purely i386.
> 
> I guess we need an evfork then. We're slowly gaining all sorts
> of functionality (various clone flags) that is inaccessible when
> there is a need for vfork behavior.

For the record, as far as I can tell, we don't need evfork() for
checkpoint-restart. So you'd need to come up with other use cases.

Oren.