fork_connector: add a fork connector

  This patch adds a fork connector in the do_fork() routine. It sends a
netlink datagram when enabled. The message can be read by a user space
application. By this way, the user space application is alerted when a
fork occurs.

  It uses the userspace <-> kernelspace connector that works on top of
the netlink protocol. The fork connector is enabled or disabled by
sending a message to the connector. The unique sequence number of
messages can be used to check if a message is lost.

  When the fork connector is disabled, the "lat_proc fork" test returns
a value equal to:
     Process fork+exit: 154.6944 microseconds
  
  When the fork connector is enabled, the same test returns:
     Process fork+exit: 165.6667 microseconds

  So the overhead (the construction and the sending of the message) is
around 7%.

  This patch applies to 2.6.11-mm4. Some other patches are needed that
fix problems in the connector.c file. At least, you need to apply the
patch provided in the second email.

Signed-off-by: Guillaume Thouvenin <guillaume.thouvenin@bull.net>
--- 

 drivers/connector/Kconfig   |   11 +++++
 drivers/connector/Makefile  |    1
 drivers/connector/cn_fork.c |   85
++++++++++++++++++++++++++++++++++++++++++++
 include/linux/connector.h   |    4 ++
 kernel/fork.c               |   44 ++++++++++++++++++++++
 5 files changed, 145 insertions(+)

Index: linux-2.6.11-mm4-cnfork/drivers/connector/Kconfig
===================================================================
--- linux-2.6.11-mm4-cnfork.orig/drivers/connector/Kconfig	2005-03-16 14:21:46.000000000
+0100
+++ linux-2.6.11-mm4-cnfork/drivers/connector/Kconfig	2005-03-16 14:34:41.000000000
+0100
@@ -10,4 +10,15 @@
 	  Connector support can also be built as a module.  If so, the module
 	  will be called cn.ko.
 
+config FORK_CONNECTOR
+	bool "Enable fork connector"
+	depends on CONNECTOR=y
+	default y
+	---help---
+	  It adds a connector in kernel/fork.c:do_fork() function. When a fork
+	  occurs, netlink is used to transfer information about the parent and 
+	  its child. This information can be used by a user space application.
+	  The fork connector can be enable/disable by sending a message to the
+	  connector with the corresponding group id.
+	  
 endmenu
Index: linux-2.6.11-mm4-cnfork/drivers/connector/Makefile
===================================================================
--- linux-2.6.11-mm4-cnfork.orig/drivers/connector/Makefile	2005-03-16 14:21:46.000000000
+0100
+++ linux-2.6.11-mm4-cnfork/drivers/connector/Makefile	2005-03-16 14:34:41.000000000
+0100
@@ -1,2 +1,3 @@
 obj-$(CONFIG_CONNECTOR)		+= cn.o
+obj-$(CONFIG_FORK_CONNECTOR)	+= cn_fork.o 
 cn-objs		:= cn_queue.o connector.o
Index: linux-2.6.11-mm4-cnfork/drivers/connector/cn_fork.c
===================================================================
--- linux-2.6.11-mm4-cnfork.orig/drivers/connector/cn_fork.c	2003-01-30 11:24:37.000000000
+0100
+++ linux-2.6.11-mm4-cnfork/drivers/connector/cn_fork.c	2005-03-16 14:34:41.000000000
+0100
@@ -0,0 +1,85 @@
+/*
+ * 	cn_fork.c
+ * 
+ * 2005 Copyright (c) Guillaume Thouvenin <guillaume.thouvenin@bull.net>
+ * All rights reserved.
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+
+#include <linux/connector.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Guillaume Thouvenin <guillaume.thouvenin@bull.net>");
+MODULE_DESCRIPTION("Enable or disable the usage of the fork connector");
+
+int cn_fork_enable = 0;
+struct cb_id cb_fork_id = { CN_IDX_FORK, CN_VAL_FORK };
+
+/**
+ * cn_fork_callback - enable or disable the fork connector
+ * @data: message send by the connector 
+ *
+ * The callback allows to enable or disable the sending of information
+ * about fork in the do_fork() routine. To enable the fork, the user 
+ * space application must send the integer 1 in the data part of the 
+ * message. To disable the fork connector, it must send the integer 0.
+ */
+static void cn_fork_callback(void *data) 
+{
+	struct cn_msg *msg = (struct cn_msg *)data;
+
+	if (cn_already_initialized && (msg->len == sizeof(cn_fork_enable)))
+		memcpy(&cn_fork_enable, msg->data, sizeof(cn_fork_enable));
+}
+
+/**
+ * cn_fork_init - initialization entry point
+ *
+ * This routine will be run at kernel boot time because this driver is
+ * built in the kernel. It adds the connector callback to the connector 
+ * driver.
+ */
+static int cn_fork_init(void)
+{
+	int err;
+	
+	err = cn_add_callback(&cb_fork_id, "cn_fork", &cn_fork_callback);
+	if (err) {
+		printk(KERN_WARNING "Failed to register cn_fork\n");
+		return -EINVAL;
+	}	
+		
+	printk(KERN_NOTICE "cn_fork is registered\n");
+	return 0;
+}
+
+/**
+ * cn_fork_exit - exit entry point
+ *
+ * As this driver is always statically compiled into the kernel the
+ * cn_fork_exit has no effect.
+ */
+static void cn_fork_exit(void)
+{
+	cn_del_callback(&cb_fork_id);
+}
+
+module_init(cn_fork_init);
+module_exit(cn_fork_exit);
Index: linux-2.6.11-mm4-cnfork/include/linux/connector.h
===================================================================
--- linux-2.6.11-mm4-cnfork.orig/include/linux/connector.h	2005-03-16 14:21:49.000000000
+0100
+++ linux-2.6.11-mm4-cnfork/include/linux/connector.h	2005-03-16 14:34:41.000000000
+0100
@@ -28,6 +28,8 @@
 #define CN_VAL_KOBJECT_UEVENT		0x0000
 #define CN_IDX_SUPERIO			0xaabb  /* SuperIO subsystem */
 #define CN_VAL_SUPERIO			0xccdd
+#define CN_IDX_FORK			0xfeed  /* fork events */
+#define CN_VAL_FORK			0xbeef
 

 #define CONNECTOR_MAX_MSG_SIZE 	1024
@@ -133,6 +135,8 @@
 };
 
 extern int cn_already_initialized;
+extern int cn_fork_enable;
+extern struct cb_id cb_fork_id;
 
 int cn_add_callback(struct cb_id *, char *, void (* callback)(void *));
 void cn_del_callback(struct cb_id *);
Index: linux-2.6.11-mm4-cnfork/kernel/fork.c
===================================================================
--- linux-2.6.11-mm4-cnfork.orig/kernel/fork.c	2005-03-16 14:21:49.000000000
+0100
+++ linux-2.6.11-mm4-cnfork/kernel/fork.c	2005-03-16 14:34:41.000000000 +0100
@@ -41,6 +41,7 @@
 #include <linux/profile.h>
 #include <linux/rmap.h>
 #include <linux/acct.h>
+#include <linux/connector.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -63,6 +64,47 @@
 
 EXPORT_SYMBOL(tasklist_lock);
 
+#ifdef CONFIG_FORK_CONNECTOR
+
+#define CN_FORK_INFO_SIZE	64
+#define CN_FORK_MSG_SIZE 	(sizeof(struct cn_msg) + CN_FORK_INFO_SIZE)
+
+static inline void fork_connector(pid_t parent, pid_t child)
+{
+	static DEFINE_SPINLOCK(cn_fork_lock);
+	static __u32 seq;   /* used to test if message is lost */
+
+	if (cn_fork_enable) {
+		struct cn_msg *msg;
+
+		__u8 buffer[CN_FORK_MSG_SIZE];	
+
+		msg = (struct cn_msg *)buffer;
+			
+		memcpy(&msg->id, &cb_fork_id, sizeof(msg->id));
+		spin_lock(&cn_fork_lock);
+		msg->seq = seq++;
+		spin_unlock(&cn_fork_lock);
+		msg->ack = 0; /* not used */
+		/* 
+		 * size of data is the number of characters 
+		 * printed plus one for the trailing '\0'
+		 */
+		/* just fill the data part with '\0' */
+		memset(msg->data, '\0', CN_FORK_INFO_SIZE);
+		msg->len = scnprintf(msg->data, CN_FORK_INFO_SIZE-1, 
+				    "%i %i", parent, child) + 1;
+
+		cn_netlink_send(msg, CN_IDX_FORK);
+	}
+}
+#else
+static inline void fork_connector(pid_t parent, pid_t child) 
+{
+	return; 
+}
+#endif /* CONFIG_FORK_CONNECTOR */
+
 int nr_processes(void)
 {
 	int cpu;
@@ -1253,6 +1295,8 @@
 			if (unlikely (current->ptrace & PT_TRACE_VFORK_DONE))
 				ptrace_notify ((PTRACE_EVENT_VFORK_DONE << 8) | SIGTRAP);
 		}
+		
+		fork_connector(current->pid, p->pid);
 	} else {
 		free_pidmap(pid);
 		pid = PTR_ERR(p);



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