From: Cedric Le Goater <clg@xxxxxxxxxx>
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@xxxxxxxxxx>
---
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
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