[patch 2.6.12-rc1-mm4] fork_connector: add a fork connector

[Guillaume Thouvenin <guillaume.thouvenin@bull.net>]

  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. In this patch we use
a cn_fork_msg structure (thanks to Dean Gaudet) rather than zeroing 64
bytes of memory and doing conversions to decimal ascii as done before.
Also we move the fork_connector() inline code in the header file
include/linux/connector.h as suggested by Paul Jackson (thanks).

  The fork connector is used by the Enhanced Linux System Accounting
project http://elsa.sourceforge.net

  When the fork connector is disabled, the "lat_proc fork" test returns
a value equal to:
     Process fork+exit: 150.2076 microseconds
  
  When the fork connector is enabled, the same test returns:
     Process fork+exit: 153.7778 microseconds

  So the overhead (the construction and the sending of the message) is
around 2%. If we use the CBUS patch http://lkml.org/lkml/2005/3/20/14 
instead of cn_netlink_send() routine we can reduce this overhead near to
0%. We're waiting for the inclusion of the CBUS in the -mm tree.  

  This patch applies to 2.6.12-rc1-mm4. 

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

 drivers/connector/Kconfig   |   11 ++++
 drivers/connector/Makefile  |    1
 drivers/connector/cn_fork.c |  104 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/connector.h   |   53 ++++++++++++++++++++++
 kernel/fork.c               |    3 +
 5 files changed, 172 insertions(+)


Index: linux-2.6.12-rc1-mm4-cnfork/drivers/connector/Kconfig
===================================================================
--- linux-2.6.12-rc1-mm4-cnfork.orig/drivers/connector/Kconfig	2005-03-31 14:56:02.000000000 +0200
+++ linux-2.6.12-rc1-mm4-cnfork/drivers/connector/Kconfig	2005-03-31 14:57:52.000000000 +0200
@@ -10,4 +10,15 @@ config CONNECTOR
 	  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-2.6.12-rc1-mm4-cnfork/drivers/connector/Makefile
===================================================================
--- linux-2.6.12-rc1-mm4-cnfork.orig/drivers/connector/Makefile	2005-03-31 14:56:02.000000000 +0200
+++ linux-2.6.12-rc1-mm4-cnfork/drivers/connector/Makefile	2005-03-31 14:57:52.000000000 +0200
@@ -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-2.6.12-rc1-mm4-cnfork/drivers/connector/cn_fork.c
===================================================================
--- linux-2.6.12-rc1-mm4-cnfork.orig/drivers/connector/cn_fork.c	2003-01-30 11:24:37.000000000 +0100
+++ linux-2.6.12-rc1-mm4-cnfork/drivers/connector/cn_fork.c	2005-03-31 14:57:52.000000000 +0200
@@ -0,0 +1,104 @@
+/*
+ * 	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 };
+
+static inline void cn_fork_send_status(void)
+{
+	/* TODO */
+	printk(KERN_INFO "cn_fork_enable == %d\n", cn_fork_enable);
+}
+
+/**
+ * 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;
+	int action;
+
+	if (cn_already_initialized && (msg->len == sizeof(cn_fork_enable))) {
+		memcpy(&action, msg->data, sizeof(cn_fork_enable));
+		switch(action) {
+			case FORK_CN_START:
+				cn_fork_enable = 1;
+				break;
+			case FORK_CN_STOP:
+				cn_fork_enable = 0;
+				break;
+			case FORK_CN_STATUS:
+				cn_fork_send_status();
+				break;
+		}
+	}
+}
+
+/**
+ * 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-2.6.12-rc1-mm4-cnfork/include/linux/connector.h
===================================================================
--- linux-2.6.12-rc1-mm4-cnfork.orig/include/linux/connector.h	2005-03-31 14:56:05.000000000 +0200
+++ linux-2.6.12-rc1-mm4-cnfork/include/linux/connector.h	2005-03-31 14:57:52.000000000 +0200
@@ -28,10 +28,16 @@
 #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
 
+#define FORK_CN_STOP	0
+#define FORK_CN_START	1
+#define FORK_CN_STATUS	2
+
 struct cb_id
 {
 	__u32			idx;
@@ -64,6 +70,12 @@ struct cn_ctl_msg
 	__u8			data[0];
 };
 
+struct cn_fork_msg
+{
+	int cpu;
+	int ppid;
+	int cpid;
+};
 
 #ifdef __KERNEL__
 
@@ -133,6 +145,8 @@ struct cn_dev
 };
 
 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 *);
@@ -146,5 +160,44 @@ void cn_queue_free_dev(struct cn_queue_d
 
 int cn_cb_equal(struct cb_id *, struct cb_id *);
 
+#ifdef CONFIG_FORK_CONNECTOR
+
+#define CN_FORK_INFO_SIZE	sizeof(struct cn_fork_msg)
+#define CN_FORK_MSG_SIZE 	(sizeof(struct cn_msg) + CN_FORK_INFO_SIZE)
+
+static DEFINE_PER_CPU(unsigned long, fork_counts);
+
+static inline void fork_connector(pid_t parent, pid_t child)
+{
+	if (cn_fork_enable) {
+		struct cn_msg *msg;
+		struct cn_fork_msg *forkmsg;
+		__u8 buffer[CN_FORK_MSG_SIZE];	
+
+		msg = (struct cn_msg *)buffer;
+			
+		memcpy(&msg->id, &cb_fork_id, sizeof(msg->id));
+		
+		msg->ack = 0; /* not used */
+		msg->seq = get_cpu_var(fork_counts)++;
+
+		msg->len = CN_FORK_INFO_SIZE;
+		forkmsg = (struct cn_fork_msg *)msg->data;
+		forkmsg->cpu = smp_processor_id();
+		forkmsg->ppid = parent;
+		forkmsg->cpid = child;
+
+		put_cpu_var(fork_counts);
+
+		cn_netlink_send(msg, CN_IDX_FORK);
+	}
+}
+#else
+static inline void fork_connector(pid_t parent, pid_t child) 
+{
+	return; 
+}
+#endif /* CONFIG_FORK_CONNECTOR */
+
 #endif /* __KERNEL__ */
 #endif /* __CONNECTOR_H */
Index: linux-2.6.12-rc1-mm4-cnfork/kernel/fork.c
===================================================================
--- linux-2.6.12-rc1-mm4-cnfork.orig/kernel/fork.c	2005-03-31 14:56:05.000000000 +0200
+++ linux-2.6.12-rc1-mm4-cnfork/kernel/fork.c	2005-03-31 14:57:52.000000000 +0200
@@ -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>
@@ -1249,6 +1250,8 @@ long do_fork(unsigned long clone_flags,
 			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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