Re: [PATCH -mm 1/5] New system call, unshare

[Al Viro <viro@ftp.linux.org.uk>]

On Fri, Dec 09, 2005 at 11:55:02AM +0100, Ingo Molnar wrote:
> 
> * JANAK DESAI <janak@us.ibm.com> wrote:
> 
> > [PATCH -mm 1/5] unshare system call: System call handler function 
> > sys_unshare
> 
> >+       if (unshare_flags & ~(CLONE_NEWNS | CLONE_VM))
> >+               goto errout;
> 
> just curious, did you consider all the other CLONE_* flags as well, to 
> see whether it makes sense to add unshare support for them?

IMO the right thing to do is
	* accept *all* flags from the very beginning
	* check constraints ("CLONE_NEWNS must be accompanied by CLONE_FS")
and either -EINVAL if they are not satisfied or silently force them.
	* for each unimplemented flag check if we corresponding thing
is shared; -EINVAL otherwise.

Then for each flag we care to implement we should replace such check with
actual unsharing - a patch per flag.

CLONE_FS and CLONE_FILES are *definitely* worth implementing and are
trivial to implement.  The only thing we must take care of is doing
all replacements under task_lock, without dropping it between updates.
I would say that CLONE_SIGHAND is also an obvious candidate for adding.