Re: [PATCH 2.6.12-rc3-mm3] connector: add a fork connector

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

ChangeLog:

  - Remove __GFP_NOFAIL flag. If an error occurred, the message is 
    just dropped.
  - Modify struct cn_fork_msg to hold the following values:
         ID of the cpu where the fork occurred,
         Parent process id, 
         Parent thread id, 
         Child process id 
         Child thread id
    All values are from a user's point of view. An explanation
    has been added in the cn_fork.h header.
  - Remove "EXPORT_SYMBOL_GPL(fork_connector);"
  - Move "extern int cn_already_initialized" in file
    include/linux/connector.h. This declaration should be
    include in the next release of the connector.
  
TODO:

  - Change the way the status is displayed. I don't know yet how to 
    do it cleanly.


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

--- 

 drivers/connector/Kconfig   |   11 +++
 drivers/connector/Makefile  |    1
 drivers/connector/cn_fork.c |  133 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/cn_fork.h     |   64 +++++++++++++++++++++
 include/linux/connector.h   |    4 +
 kernel/fork.c               |    4 +
 6 files changed, 217 insertions(+)

Index: linux-2.6.12-rc3-mm3/drivers/connector/Kconfig
===================================================================
--- linux-2.6.12-rc3-mm3.orig/drivers/connector/Kconfig	2005-05-09 07:45:52.000000000 +0200
+++ linux-2.6.12-rc3-mm3/drivers/connector/Kconfig	2005-05-09 08:03:15.000000000 +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"
+	select CONNECTOR
+	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-rc3-mm3/drivers/connector/Makefile
===================================================================
--- linux-2.6.12-rc3-mm3.orig/drivers/connector/Makefile	2005-05-09 07:45:52.000000000 +0200
+++ linux-2.6.12-rc3-mm3/drivers/connector/Makefile	2005-05-09 08:03:15.000000000 +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-rc3-mm3/drivers/connector/cn_fork.c
===================================================================
--- linux-2.6.12-rc3-mm3.orig/drivers/connector/cn_fork.c	2003-01-30 11:24:37.000000000 +0100
+++ linux-2.6.12-rc3-mm3/drivers/connector/cn_fork.c	2005-05-10 09:40:08.000000000 +0200
@@ -0,0 +1,133 @@
+/*
+ * cn_fork.c - Fork connector
+ *
+ * Copyright (C) 2005 BULL SA.
+ * Written by Guillaume Thouvenin <guillaume.thouvenin@bull.net>
+ * 
+ * This module implements the fork connector. It allows to send a
+ * netlink datagram, when enabled, from the do_fork() routine. 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.  
+ *
+ * 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/cn_fork.h>
+
+#define CN_FORK_INFO_SIZE	sizeof(struct cn_fork_msg)
+#define CN_FORK_MSG_SIZE 	(sizeof(struct cn_msg) + CN_FORK_INFO_SIZE)
+
+static int cn_fork_enable = 0;
+struct cb_id cb_fork_id = { CN_IDX_FORK, CN_VAL_FORK };
+
+/* fork_counts is used as the sequence number of the netlink message */
+static DEFINE_PER_CPU(unsigned long, fork_counts);
+
+void fork_connector(pid_t ppid, pid_t ptid, pid_t cpid, pid_t ctid)
+{
+	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 = ppid;
+		forkmsg->ptid = ptid;
+		forkmsg->cpid = cpid;
+		forkmsg->ctid = ctid;
+
+		put_cpu_var(fork_counts);
+
+		/*  If cn_netlink_send() failed, the data is not send */
+		cn_netlink_send(msg, CN_IDX_FORK, GFP_KERNEL);
+	}
+}
+
+static inline void cn_fork_send_status(void)
+{
+	/* TODO: An informational line in log is maybe not enough... */
+	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 = 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.
+ */
+int __init 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;
+}
+
+__initcall(cn_fork_init);
Index: linux-2.6.12-rc3-mm3/include/linux/cn_fork.h
===================================================================
--- linux-2.6.12-rc3-mm3.orig/include/linux/cn_fork.h	2003-01-30 11:24:37.000000000 +0100
+++ linux-2.6.12-rc3-mm3/include/linux/cn_fork.h	2005-05-10 11:27:49.000000000 +0200
@@ -0,0 +1,64 @@
+/*
+ * cn_fork.h - Fork connector
+ *
+ * Copyright (C) 2005 Nguyen Anh Quynh <aquynh@gmail.com>
+ * Copyright (C) 2005 Guillaume Thouvenin <guillaume.thouvenin@bull.net>
+ * 
+ * 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
+ */
+
+#ifndef CN_FORK_H
+#define CN_FORK_H
+
+#include <linux/connector.h>
+
+#define FORK_CN_STOP	0
+#define FORK_CN_START	1
+#define FORK_CN_STATUS	2
+
+/*
+ * The fork connector sends information to a user-space 
+ * application. From the user's point of view, the process 
+ * ID is the thread group ID and thread ID is the internal
+ * kernel "pid". So, fields are assigned as follow:
+ *
+ *  In user space     -  In  kernel space 
+ *                    
+ * parent process ID  =  parent->tgid
+ * parent thread  ID  =  parent->pid
+ * child  process ID  =  child->tgid
+ * child  thread  ID  =  child->pid
+ */
+struct cn_fork_msg {
+	int cpu;		/* ID of the cpu where the fork occured */
+	pid_t ppid;		/* parent process ID */
+	pid_t ptid;		/* parent thread ID  */
+	pid_t cpid;		/* child process ID  */
+	pid_t ctid;		/* child thread ID   */
+};
+
+/* Code above is only inside the kernel */
+#ifdef __KERNEL__
+#ifdef CONFIG_FORK_CONNECTOR
+extern void fork_connector(pid_t ppid, pid_t ptid, pid_t cpid, pid_t ctid);
+#else
+static inline void fork_connector(pid_t ppid, pid_t ptid, pid_t cpid,
+				  pid_t ctid);
+{
+	return;
+}
+#endif				/* CONFIG_FORK_CONNECTOR */
+#endif				/* __KERNEL__ */
+#endif				/* CN_FORK_H */
Index: linux-2.6.12-rc3-mm3/include/linux/connector.h
===================================================================
--- linux-2.6.12-rc3-mm3.orig/include/linux/connector.h	2005-05-09 07:45:56.000000000 +0200
+++ linux-2.6.12-rc3-mm3/include/linux/connector.h	2005-05-10 10:27:43.000000000 +0200
@@ -26,6 +26,8 @@
 
 #define CN_IDX_CONNECTOR		0xffffffff
 #define CN_VAL_CONNECTOR		0xffffffff
+#define CN_IDX_FORK			0xfeed  /* fork events */
+#define CN_VAL_FORK			0xbeef
 
 /*
  * Maximum connector's message size.
@@ -137,6 +139,8 @@ struct cn_dev {
 	struct cn_queue_dev *cbdev;
 };
 
+extern int cn_already_initialized;
+
 int cn_add_callback(struct cb_id *, char *, void (*callback) (void *));
 void cn_del_callback(struct cb_id *);
 int cn_netlink_send(struct cn_msg *, u32, int);
Index: linux-2.6.12-rc3-mm3/kernel/fork.c
===================================================================
--- linux-2.6.12-rc3-mm3.orig/kernel/fork.c	2005-05-09 07:45:56.000000000 +0200
+++ linux-2.6.12-rc3-mm3/kernel/fork.c	2005-05-10 11:26:08.000000000 +0200
@@ -41,6 +41,7 @@
 #include <linux/profile.h>
 #include <linux/rmap.h>
 #include <linux/acct.h>
+#include <linux/cn_fork.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -1252,6 +1253,9 @@ 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->tgid, current->pid,
+		               p->tgid, p->pid);
 	} else {
 		free_pidmap(pid);
 		pid = PTR_ERR(p);


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