From: Arnd Bergmann <arnd@arndb.de>
To: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Subject: Re: [RFC][v7][PATCH 8/9]: Define clone2() syscall
Date: Thu, 24 Sep 2009 23:43:59 +0200
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Cc: linux-kernel@vger.kernel.org, Oren Laadan <orenl@cs.columbia.edu>,
       serue@us.ibm.com, "Eric W. Biederman" <ebiederm@xmission.com>,
       Alexey Dobriyan <adobriyan@gmail.com>,
       Pavel Emelyanov <xemul@openvz.org>, Andrew Morton <akpm@osdl.org>,
       torvalds@linux-foundation.org, mikew@google.com, mingo@elte.hu,
       hpa@zytor.com, Nathan Lynch <nathanl@austin.ibm.com>,
       peterz@infradead.org,
       Containers <containers@lists.linux-foundation.org>, sukadev@us.ibm.com
References: <20090924165548.GA16586@us.ibm.com> <20090924170308.GH16989@us.ibm.com>
In-Reply-To: <20090924170308.GH16989@us.ibm.com>
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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.

	Arnd <><
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