extend clone_flags using parent_tidptr argument

From: Cedric Le Goater <[email protected]>

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 <[email protected]>

---
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
===================================================================

include/linux/sched.h +1 -0

@@ -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
===================================================================

kernel/fork.c +13 -1

@@ -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

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Quoted 5 lines · Cedric Le Goater

From: Cedric Le Goater <[email protected]>

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?

Quoted 6 lines · On Mon, 4 Feb 2008 14:24:16 -0600 "Serge E. Hallyn" <[email protected]> wrote:

Quoted 3 lines · Cedric Le Goater

From: Cedric Le Goater <[email protected]>

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