[PATCH 2/2] extend clone_flags using parent_tidptr argument

[PATCH 2/2] extend clone_flags using parent_tidptr argument

[Cedric Le Goater]

From: Cedric Le Goater <clg@fr.ibm.com>

We have at least 2 patchsets requiring each a new clone flag and 
there it is, we've reached the limit, none are left.  

This patch uses the CLONE_DETACHED flag (unused) as a marker to 
extend the clone flags through the parent_tidptr argument.

Initially, we thought on using the last bit but it has recently 
been taken by CLONE_IO.

Obviously, this hack doesn't work for unshare() for which I don't 
see any other solution than to add a new syscall : 

	long sys_unshare64(unsigned long clone_flags_high, 
			unsigned long clone_flags_low);



Is this the right path to extend the clone flags ? should we add a 
clone64() rather than hack the extending clone() ? 

Thanks for any comments !

C.

Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
---
 include/linux/sched.h |    1 +
 kernel/fork.c         |   14 +++++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

Index: 2.6.24-mm1/include/linux/sched.h
===================================================================
--- 2.6.24-mm1.orig/include/linux/sched.h
+++ 2.6.24-mm1/include/linux/sched.h
@@ -28,6 +28,7 @@
 #define CLONE_NEWPID		0x20000000	/* New pid namespace */
 #define CLONE_NEWNET		0x40000000	/* New network namespace */
 #define CLONE_IO		0x80000000	/* Clone io context */
+#define CLONE_EXTFLAGS		CLONE_DETACHED	/* use parent_tidptr as an extended set of flags */
 
 /*
  * Scheduling policies
Index: 2.6.24-mm1/kernel/fork.c
===================================================================
--- 2.6.24-mm1.orig/kernel/fork.c
+++ 2.6.24-mm1/kernel/fork.c
@@ -1012,6 +1012,14 @@ static struct task_struct *copy_process(
 	struct task_struct *p;
 	int cgroup_callbacks_done = 0;
 
+	/*
+	 * It is not permitted to specify both CLONE_EXTFLAGS and
+	 * CLONE_PARENT_SETTID
+	 */
+	if ((clone_flags & (CLONE_EXTFLAGS|CLONE_PARENT_SETTID)) ==
+	    (CLONE_EXTFLAGS|CLONE_PARENT_SETTID))
+		return ERR_PTR(-EINVAL);
+
 	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
 		return ERR_PTR(-EINVAL);
 
@@ -1455,6 +1463,7 @@ long do_fork(unsigned long clone_flags,
 	struct task_struct *p;
 	int trace = 0;
 	long nr;
+	u64 clone_flags64 = clone_flags;
 
 	/*
 	 * We hope to recycle these flags after 2.6.26
@@ -1479,7 +1488,10 @@ long do_fork(unsigned long clone_flags,
 			clone_flags |= CLONE_PTRACE;
 	}
 
-	p = copy_process(clone_flags, stack_start, regs, stack_size,
+	if (clone_flags & CLONE_EXTFLAGS)
+		clone_flags64 = ((u64) (uintptr_t) parent_tidptr << 32) | clone_flags;
+
+	p = copy_process(clone_flags64, stack_start, regs, stack_size,
 			child_tidptr, NULL);
 	/*
 	 * Do this prior waking up the new thread - the thread pointer

Re: [PATCH 2/2] extend clone_flags using parent_tidptr argument

[Serge E. Hallyn]

Quoting Cedric Le Goater (legoater@free.fr):
> From: Cedric Le Goater <clg@fr.ibm.com>
>
> We have at least 2 patchsets requiring each a new clone flag and there it 
> is, we've reached the limit, none are left.  
> This patch uses the CLONE_DETACHED flag (unused) as a marker to extend the 

Are we pretty sure that there is no legacy software out there which has
continued to specify CLONE_DETACHED since the kernel ignores it?

> clone flags through the parent_tidptr argument.
>
> Initially, we thought on using the last bit but it has recently been taken 
> by CLONE_IO.
>
> Obviously, this hack doesn't work for unshare() for which I don't see any 
> other solution than to add a new syscall : 
> 	long sys_unshare64(unsigned long clone_flags_high, 			unsigned long 
> clone_flags_low);
>
>
>
> Is this the right path to extend the clone flags ? should we add a 
> clone64() rather than hack the extending clone() ? 
> Thanks for any comments !
>
> C.
>
> Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
> ---
> include/linux/sched.h |    1 +
> kernel/fork.c         |   14 +++++++++++++-
> 2 files changed, 14 insertions(+), 1 deletion(-)
>
> Index: 2.6.24-mm1/include/linux/sched.h
> ===================================================================
> --- 2.6.24-mm1.orig/include/linux/sched.h
> +++ 2.6.24-mm1/include/linux/sched.h
> @@ -28,6 +28,7 @@
> #define CLONE_NEWPID		0x20000000	/* New pid namespace */
> #define CLONE_NEWNET		0x40000000	/* New network namespace */
> #define CLONE_IO		0x80000000	/* Clone io context */
> +#define CLONE_EXTFLAGS		CLONE_DETACHED	/* use parent_tidptr as an extended 
> set of flags */
>
> /*
>  * Scheduling policies
> Index: 2.6.24-mm1/kernel/fork.c
> ===================================================================
> --- 2.6.24-mm1.orig/kernel/fork.c
> +++ 2.6.24-mm1/kernel/fork.c
> @@ -1012,6 +1012,14 @@ static struct task_struct *copy_process(
> 	struct task_struct *p;
> 	int cgroup_callbacks_done = 0;
>
> +	/*
> +	 * It is not permitted to specify both CLONE_EXTFLAGS and
> +	 * CLONE_PARENT_SETTID
> +	 */
> +	if ((clone_flags & (CLONE_EXTFLAGS|CLONE_PARENT_SETTID)) ==
> +	    (CLONE_EXTFLAGS|CLONE_PARENT_SETTID))
> +		return ERR_PTR(-EINVAL);
> +
> 	if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
> 		return ERR_PTR(-EINVAL);
>
> @@ -1455,6 +1463,7 @@ long do_fork(unsigned long clone_flags,
> 	struct task_struct *p;
> 	int trace = 0;
> 	long nr;
> +	u64 clone_flags64 = clone_flags;
>
> 	/*
> 	 * We hope to recycle these flags after 2.6.26
> @@ -1479,7 +1488,10 @@ long do_fork(unsigned long clone_flags,
> 			clone_flags |= CLONE_PTRACE;
> 	}
>
> -	p = copy_process(clone_flags, stack_start, regs, stack_size,
> +	if (clone_flags & CLONE_EXTFLAGS)
> +		clone_flags64 = ((u64) (uintptr_t) parent_tidptr << 32) | clone_flags;
> +
> +	p = copy_process(clone_flags64, stack_start, regs, stack_size,
> 			child_tidptr, NULL);
> 	/*
> 	 * Do this prior waking up the new thread - the thread pointer
> _______________________________________________
> Containers mailing list
> Containers@lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/containers

Re: [PATCH 2/2] extend clone_flags using parent_tidptr argument

[Andrew Morton]

On Mon, 4 Feb 2008 14:24:16 -0600
"Serge E. Hallyn" <serue@us.ibm.com> wrote:

> Quoting Cedric Le Goater (legoater@free.fr):
> > From: Cedric Le Goater <clg@fr.ibm.com>
> >
> > We have at least 2 patchsets requiring each a new clone flag and there it 
> > is, we've reached the limit, none are left.  
> > This patch uses the CLONE_DETACHED flag (unused) as a marker to extend the 
> 
> Are we pretty sure that there is no legacy software out there which has
> continued to specify CLONE_DETACHED since the kernel ignores it?

Please see -mm's
clone-prepare-to-recycle-clone_detached-and-clone_stopped.patch

That patch has been cut back to only recycle CLONE_STOPPED because there
indeed was software out there which is setting CLONE_DETACHED.

See http://linux.derkeiler.com/Mailing-Lists/Kernel/2007-11/msg04293.html

Re: [PATCH 2/2] extend clone_flags using parent_tidptr argument

[Cedric Le Goater]

Andrew Morton wrote:
> On Mon, 4 Feb 2008 14:24:16 -0600
> "Serge E. Hallyn" <serue@us.ibm.com> wrote:
> 
>> Quoting Cedric Le Goater (legoater@free.fr):
>>> From: Cedric Le Goater <clg@fr.ibm.com>
>>>
>>> We have at least 2 patchsets requiring each a new clone flag and there it 
>>> is, we've reached the limit, none are left.  
>>> This patch uses the CLONE_DETACHED flag (unused) as a marker to extend the 
>> Are we pretty sure that there is no legacy software out there which has
>> continued to specify CLONE_DETACHED since the kernel ignores it?
> 
> Please see -mm's
> clone-prepare-to-recycle-clone_detached-and-clone_stopped.patch
> 
> That patch has been cut back to only recycle CLONE_STOPPED because there
> indeed was software out there which is setting CLONE_DETACHED.
> 
> See http://linux.derkeiler.com/Mailing-Lists/Kernel/2007-11/msg04293.html

bummer, I used the wrong one :/
 
Thanks,

C.