linux-kernel - Re: [RFC][v7][PATCH 8/9]: Define clone2() syscall

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Message-ID: <20090925082346.GB4436@localdomain>
Date:	Fri, 25 Sep 2009 10:23:47 +0200
From:	Louis Rilling <Louis.Rilling@...labs.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	Containers <containers@...ts.linux-foundation.org>,
	Nathan Lynch <nathanl@...tin.ibm.com>,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>, hpa@...or.com,
	mingo@...e.hu, torvalds@...ux-foundation.org,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [RFC][v7][PATCH 8/9]: Define clone2() syscall

On Thu, Sep 24, 2009 at 11:43:59PM +0200, Arnd Bergmann wrote:
> On Thursday 24 September 2009, Sukadev Bhattiprolu wrote:
> > +asmlinkage long
> > +sys_clone2(struct clone_struct __user *ucs, pid_t __user *pids)
> > +{
> > +       int rc;
> > +       struct clone_struct kcs;
> > +       unsigned long clone_flags;
> > +       int __user *parent_tid_ptr;
> > +       int __user *child_tid_ptr;
> > +       unsigned long __user child_stack_base;
> > +       struct pt_regs *regs;
> > +
> > +       rc = copy_from_user(&ucs, &kcs, sizeof(kcs));
> > +       if (rc)
> > +               return -EFAULT;
> > +
> > +       /*
> > +        * TODO: Convert clone_flags to 64-bit
> > +        */
> > +       clone_flags = (unsigned long)kcs.flags;
> > +       child_stack_base = (unsigned long)kcs.child_stack;
> > +       parent_tid_ptr = &ucs.parent_tid;
> > +       child_tid_ptr =  &ucs.child_tid;
> > +       regs = task_pt_regs(current);
> > +
> > +       if (!child_stack_base)
> > +               child_stack_base = user_stack_pointer(regs);
> > +
> > +       return do_fork_with_pids(clone_flags, child_stack_base, regs, 0,
> > +                       parent_tid_ptr, child_tid_ptr, kcs.nr_pids, pids);
> > +}
> > +
> 
> The function looks ok, but you have put it into arch/x86/kernel/process_32.c,
> which is specific to x86-32. Since the code in this form is generic, why
> not just put it into kernel/fork.c? You should probably enclose it within
> #ifdef CONFIG_HAVE_ARCH_TRACEHOOK to make sure that user_stack_pointer()
> is implemented, but then it would be immediately usable by the nine architectures
> implementing that. The other architectures can then decide between adding
> their private version of sys_clone2 with an open-coded user_stack_pointer
> implementation or alternatively implement the tracehooks.

It will very likely break ia64, which defines CONFIG_HAVE_ARCH_TRACEHOOK and
already has sys_clone2().

Louis

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