From: Jerome Marchand <jmarchan@redhat.com>
Date: Tue, 3 Mar 2009 17:27:24 +0100
Subject: [misc] auxiliary signal structure: signal_struct_aux
Message-id: 20090303162957.223238567@dhcp-0-152.brq.redhat.com
O-Subject: [RHEL5.4 Patch 02/12] Auxiliary signal structure: signal_struct_aux
Bugzilla: 461636
RH-Acked-by: Jeff Moyer <jmoyer@redhat.com>

bz461636

Patch from Oleg Nesterov:

Introduce signal_struct_aux. Since we can't change "struct signal_struct",
we change the size of the allocated objects. The aux info is placed right
after the end of the kABI-visible part of the object, and can be accessed
via the new signal_aux(sig) helper with no overhead.

Currently signal_struct_aux is empty and init_signal_aux(*aux) does nothing,
further patches will populate it.

diff --git a/include/linux/init_signals.h b/include/linux/init_signals.h
index eea0f8b..8ab4a09 100644
--- a/include/linux/init_signals.h
+++ b/include/linux/init_signals.h
@@ -1 +1,5 @@
-static struct signal_struct init_signals = INIT_SIGNALS(init_signals);
+static struct signal_with_aux_struct init_signals_aux = {
+	.sig = INIT_SIGNALS(init_signals_aux.sig),
+};
+
+#define init_signals	init_signals_aux.sig
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d2ec53c..42883af 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -521,6 +521,23 @@ struct signal_struct {
 #endif
 };
 
+struct signal_struct_aux {
+};
+
+static inline void init_signal_aux(struct signal_struct_aux *aux)
+{
+}
+
+struct signal_with_aux_struct {
+	struct signal_struct		sig;
+	struct signal_struct_aux	aux;
+};
+
+static inline struct signal_struct_aux *signal_aux(struct signal_struct *sig)
+{
+	return &container_of(sig, struct signal_with_aux_struct, sig)->aux;
+}
+
 /* Context switch must be unlocked if interrupts are to be enabled */
 #ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
 # define __ARCH_WANT_UNLOCKED_CTXSW
diff --git a/kernel/fork.c b/kernel/fork.c
index e747257..b7508e3 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -965,6 +965,8 @@ static inline int copy_signal(unsigned long clone_flags, struct task_struct * ts
 	if (!sig)
 		return -ENOMEM;
 
+	init_signal_aux(signal_aux(sig));
+
 	ret = copy_thread_group_keys(tsk);
 	if (ret < 0) {
 		kmem_cache_free(signal_cachep, sig);
@@ -1539,7 +1541,7 @@ void __init proc_caches_init(void)
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU,
 			sighand_ctor, NULL);
 	signal_cachep = kmem_cache_create("signal_cache",
-			sizeof(struct signal_struct), 0,
+			sizeof(struct signal_with_aux_struct), 0,
 			SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
 	files_cachep = kmem_cache_create("files_cache", 
 			sizeof(struct files_struct), 0,