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 <[email protected]>
---
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 <[email protected]>
+ * 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 <[email protected]>");
+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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