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SubjectRe: [PATCH 2.6.11-rc4-mm1] connector: Add a fork connector
On Thu, 24 Feb 2005 11:24:37 +0100, Guillaume Thouvenin
<guillaume.thouvenin@bull.net> wrote:
> This patch replaces the relay_fork module and it implements a fork
> connector in the kernel/fork.c:do_fork() routine. It applies on a kernel
> 2.6.11-rc4-mm1. The connector sends information about parent PID and
> child PID over a netlink interface. It allows to several user space
> applications to be informed when a fork occurs in the kernel. The main
> drawback is that even if nobody listens, message is send. I don't know
> how to avoid that.
>
> It is used by ELSA to manage group of processes in user space and can
> be used by any other user space application that needs this kind of
> information.
>
> I add a callback that turns on/off the fork connector. It's a very
> simple mechanism and, as Evgeniy suggested, it may need a more complex
> protocol.
>
> ChangeLog:
>
> - "fork_id" is now declared as a static const
> - Replace snprintf() by scnprintf()
> - Protect "seq" by a spin lock because the seq number can be
> used by the daemon to check if all forks are intercepted
> - "msg" send is now local
> - Add a callback that turns on/off the fork connector.
> - memset is only used to clear the msg->data part instead of all
> message.
>
> Todo:
>
> - Test the performance impact with lmbench
> - Improve the callback that turns on/off the fork connector
> - Create a specific module to register the callback.
>
> Thanks to Andrew, Evgeniy and everyone for the comments,
> Guillaume
>
> Signed-off-by: Guillaume Thouvenin <guillaume.thouvenin@bull.net>
>
> ---
>
> drivers/connector/Kconfig | 11 ++++++++++
> drivers/connector/connector.c | 20 ++++++++++++++++++
> include/linux/connector.h | 3 ++
> kernel/fork.c | 45 ++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 79 insertions(+)
>
> diff -uprN -X dontdiff linux-2.6.11-rc4-mm1/drivers/connector/connector.c linux-2.6.11-rc4-mm1-cnfork/drivers/connector/connector.c
> --- linux-2.6.11-rc4-mm1/drivers/connector/connector.c 2005-02-23 11:12:15.000000000 +0100
> +++ linux-2.6.11-rc4-mm1-cnfork/drivers/connector/connector.c 2005-02-24 10:21:59.000000000 +0100
> @@ -45,8 +45,10 @@ static DEFINE_SPINLOCK(notify_lock);
> static LIST_HEAD(notify_list);
>
> static struct cn_dev cdev;
> +static struct cb_id cn_fork_id = { CN_IDX_FORK, CN_VAL_FORK };
>
> int cn_already_initialized = 0;
> +int cn_fork_enable = 0;
>
> /*
> * msg->seq and msg->ack are used to determine message genealogy.
> @@ -467,6 +469,14 @@ static void cn_callback(void * data)
> }
> }
>
> +static void cn_fork_callback(void *data)
> +{
> + if (cn_already_initialized)
> + cn_fork_enable = cn_fork_enable ? 0 : 1;
> +
> + printk(KERN_NOTICE "cn_fork_enable is set to %i\n", cn_fork_enable);
> +}
> +
> static int cn_init(void)
> {
> struct cn_dev *dev = &cdev;
> @@ -498,6 +508,15 @@ static int cn_init(void)
> return -EINVAL;
> }
>
> + err = cn_add_callback(&cn_fork_id, "cn_fork", &cn_fork_callback);
> + if (err) {
> + cn_del_callback(&dev->id);
> + cn_queue_free_dev(dev->cbdev);
> + if (dev->nls->sk_socket)
> + sock_release(dev->nls->sk_socket);
> + return -EINVAL;
> + }
> +
> cn_already_initialized = 1;
>
> return 0;
> @@ -507,6 +526,7 @@ static void cn_fini(void)
> {
> struct cn_dev *dev = &cdev;
>
> + cn_del_callback(&cn_fork_id);
> cn_del_callback(&dev->id);
> cn_queue_free_dev(dev->cbdev);
> if (dev->nls->sk_socket)
> diff -uprN -X dontdiff linux-2.6.11-rc4-mm1/drivers/connector/Kconfig linux-2.6.11-rc4-mm1-cnfork/drivers/connector/Kconfig
> --- linux-2.6.11-rc4-mm1/drivers/connector/Kconfig 2005-02-23 11:12:15.000000000 +0100
> +++ linux-2.6.11-rc4-mm1-cnfork/drivers/connector/Kconfig 2005-02-24 10:29:11.000000000 +0100
> @@ -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
> diff -uprN -X dontdiff linux-2.6.11-rc4-mm1/include/linux/connector.h linux-2.6.11-rc4-mm1-cnfork/include/linux/connector.h
> --- linux-2.6.11-rc4-mm1/include/linux/connector.h 2005-02-23 11:12:17.000000000 +0100
> +++ linux-2.6.11-rc4-mm1-cnfork/include/linux/connector.h 2005-02-24 10:25:22.000000000 +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 +135,7 @@ struct cn_dev
> };
>
> extern int cn_already_initialized;
> +extern int cn_fork_enable;
>
> int cn_add_callback(struct cb_id *, char *, void (* callback)(void *));
> void cn_del_callback(struct cb_id *);
> diff -uprN -X dontdiff linux-2.6.11-rc4-mm1/kernel/fork.c linux-2.6.11-rc4-mm1-cnfork/kernel/fork.c
> --- linux-2.6.11-rc4-mm1/kernel/fork.c 2005-02-23 11:12:17.000000000 +0100
> +++ linux-2.6.11-rc4-mm1-cnfork/kernel/fork.c 2005-02-24 10:27:02.000000000 +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 +64,48 @@ DEFINE_PER_CPU(unsigned long, process_co
>
> 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
> +
> +spinlock_t fork_cn_lock = SPIN_LOCK_UNLOCKED;
> +
> +static inline void fork_connector(pid_t parent, pid_t child)
> +{
> + static const struct cb_id fork_id = { CN_IDX_FORK, CN_VAL_FORK };
> + 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, &fork_id, sizeof(msg->id));
> + spin_lock(&fork_cn_lock);
> + msg->seq = seq++;
> + spin_unlock(&fork_cn_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
> +
> int nr_processes(void)
> {
> int cpu;
> @@ -1238,6 +1281,8 @@ 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);

Guillaume, I see that you are trying to discover if the kernel has
CONFIG_FORK_CONNECTOR defined or not. In case CONFIG_FORK_CONNECTOR is
not defined, you will call a "dummy" fork_connector (which just call
"return"). But why you dont move the checking to where you call
fork_connector? In this case, if CONFIG_FORK_CONNECTOR is not defined,
nothing called, and of course you dont need a "dummy" fork_connector
like in the above code.

Just try something like this:

+#ifdef CONFIG_FORK_CONNECTOR
+
+ fork_connector(current->pid, p->pid);
#endif

regards,
AQ
-
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