[patch 1/1] proc connector: add event for process becoming session leader

[patch 1/1] proc connector: add event for process becoming session leader

[akpm]

From: Scott James Remnant <scott@ubuntu.com>

The act of a process becoming a session leader is a useful signal to a
supervising init daemon such as Upstart.

While a daemon will normally do this as part of the process of becoming a
daemon, it is rare for its children to do so.  When the children do, it is
nearly always a sign that the child should be considered detached from the
parent and not supervised along with it.

The poster-child example is OpenSSH; the per-login children call setsid()
so that they may control the pty connected to them.  If the primary daemon
dies or is restarted, we do not want to consider the per-login children
and want to respawn the primary daemon without killing the children.

This patch adds a new PROC_SID_EVENT and associated structure to the
proc_event event_data union, it arranges for this to be emitted when the
special PIDTYPE_SID pid is set.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Scott James Remnant <scott@ubuntu.com>
Acked-by: Matt Helsley <matthltc@us.ibm.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/connector/cn_proc.c |   25 +++++++++++++++++++++++++
 include/linux/cn_proc.h     |   10 ++++++++++
 kernel/exit.c               |    4 +++-
 3 files changed, 38 insertions(+), 1 deletion(-)

diff -puN drivers/connector/cn_proc.c~proc-connector-add-event-for-process-becoming-session-leader drivers/connector/cn_proc.c
--- a/drivers/connector/cn_proc.c~proc-connector-add-event-for-process-becoming-session-leader
+++ a/drivers/connector/cn_proc.c
@@ -139,6 +139,31 @@ void proc_id_connector(struct task_struc
 	cn_netlink_send(msg, CN_IDX_PROC, GFP_KERNEL);
 }
 
+void proc_sid_connector(struct task_struct *task)
+{
+	struct cn_msg *msg;
+	struct proc_event *ev;
+	struct timespec ts;
+	__u8 buffer[CN_PROC_MSG_SIZE];
+
+	if (atomic_read(&proc_event_num_listeners) < 1)
+		return;
+
+	msg = (struct cn_msg *)buffer;
+	ev = (struct proc_event *)msg->data;
+	get_seq(&msg->seq, &ev->cpu);
+	ktime_get_ts(&ts); /* get high res monotonic timestamp */
+	put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);
+	ev->what = PROC_EVENT_SID;
+	ev->event_data.sid.process_pid = task->pid;
+	ev->event_data.sid.process_tgid = task->tgid;
+
+	memcpy(&msg->id, &cn_proc_event_id, sizeof(msg->id));
+	msg->ack = 0; /* not used */
+	msg->len = sizeof(*ev);
+	cn_netlink_send(msg, CN_IDX_PROC, GFP_KERNEL);
+}
+
 void proc_exit_connector(struct task_struct *task)
 {
 	struct cn_msg *msg;
diff -puN include/linux/cn_proc.h~proc-connector-add-event-for-process-becoming-session-leader include/linux/cn_proc.h
--- a/include/linux/cn_proc.h~proc-connector-add-event-for-process-becoming-session-leader
+++ a/include/linux/cn_proc.h
@@ -52,6 +52,7 @@ struct proc_event {
 		PROC_EVENT_EXEC = 0x00000002,
 		PROC_EVENT_UID  = 0x00000004,
 		PROC_EVENT_GID  = 0x00000040,
+		PROC_EVENT_SID  = 0x00000080,
 		/* "next" should be 0x00000400 */
 		/* "last" is the last process event: exit */
 		PROC_EVENT_EXIT = 0x80000000
@@ -89,6 +90,11 @@ struct proc_event {
 			} e;
 		} id;
 
+		struct sid_proc_event {
+			__kernel_pid_t process_pid;
+			__kernel_pid_t process_tgid;
+		} sid;
+
 		struct exit_proc_event {
 			__kernel_pid_t process_pid;
 			__kernel_pid_t process_tgid;
@@ -102,6 +108,7 @@ struct proc_event {
 void proc_fork_connector(struct task_struct *task);
 void proc_exec_connector(struct task_struct *task);
 void proc_id_connector(struct task_struct *task, int which_id);
+void proc_sid_connector(struct task_struct *task);
 void proc_exit_connector(struct task_struct *task);
 #else
 static inline void proc_fork_connector(struct task_struct *task)
@@ -114,6 +121,9 @@ static inline void proc_id_connector(str
 				     int which_id)
 {}
 
+static inline void proc_sid_connector(struct task_struct *task)
+{}
+
 static inline void proc_exit_connector(struct task_struct *task)
 {}
 #endif	/* CONFIG_PROC_EVENTS */
diff -puN kernel/exit.c~proc-connector-add-event-for-process-becoming-session-leader kernel/exit.c
--- a/kernel/exit.c~proc-connector-add-event-for-process-becoming-session-leader
+++ a/kernel/exit.c
@@ -359,8 +359,10 @@ void __set_special_pids(struct pid *pid)
 {
 	struct task_struct *curr = current->group_leader;
 
-	if (task_session(curr) != pid)
+	if (task_session(curr) != pid) {
 		change_pid(curr, PIDTYPE_SID, pid);
+		proc_sid_connector(curr);
+	}
 
 	if (task_pgrp(curr) != pid)
 		change_pid(curr, PIDTYPE_PGID, pid);
_

Re: [patch 1/1] proc connector: add event for process becoming session leader

[David Miller]

From: akpm@linux-foundation.org
Date: Thu, 06 Aug 2009 16:05:47 -0700

> From: Scott James Remnant <scott@ubuntu.com>
> 
> The act of a process becoming a session leader is a useful signal to a
> supervising init daemon such as Upstart.
> 
> While a daemon will normally do this as part of the process of becoming a
> daemon, it is rare for its children to do so.  When the children do, it is
> nearly always a sign that the child should be considered detached from the
> parent and not supervised along with it.
> 
> The poster-child example is OpenSSH; the per-login children call setsid()
> so that they may control the pty connected to them.  If the primary daemon
> dies or is restarted, we do not want to consider the per-login children
> and want to respawn the primary daemon without killing the children.
> 
> This patch adds a new PROC_SID_EVENT and associated structure to the
> proc_event event_data union, it arranges for this to be emitted when the
> special PIDTYPE_SID pid is set.
> 
> [akpm@linux-foundation.org: coding-style fixes]
> Signed-off-by: Scott James Remnant <scott@ubuntu.com>
> Acked-by: Matt Helsley <matthltc@us.ibm.com>
> Cc: Oleg Nesterov <oleg@tv-sign.ru>
> Cc: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
> Cc: "David S. Miller" <davem@davemloft.net>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Acked-by: David S. Miller <davem@davemloft.net>

This is more process handling level stuff than actual networking
or connector bits, so it should probably be merged via akpm's
usual patch bombs or some other relevant tree.

Andrew, if you really want, I can take this into net-next-2.6

Re: [patch 1/1] proc connector: add event for process becoming session leader

[Andrew Morton]

On Wed, 12 Aug 2009 17:32:03 -0700 (PDT) David Miller <davem@davemloft.net> wrote:

> From: akpm@linux-foundation.org
> Date: Thu, 06 Aug 2009 16:05:47 -0700
> 
> > From: Scott James Remnant <scott@ubuntu.com>
> > 
> > The act of a process becoming a session leader is a useful signal to a
> > supervising init daemon such as Upstart.
> > 
> > While a daemon will normally do this as part of the process of becoming a
> > daemon, it is rare for its children to do so.  When the children do, it is
> > nearly always a sign that the child should be considered detached from the
> > parent and not supervised along with it.
> > 
> > The poster-child example is OpenSSH; the per-login children call setsid()
> > so that they may control the pty connected to them.  If the primary daemon
> > dies or is restarted, we do not want to consider the per-login children
> > and want to respawn the primary daemon without killing the children.
> > 
> > This patch adds a new PROC_SID_EVENT and associated structure to the
> > proc_event event_data union, it arranges for this to be emitted when the
> > special PIDTYPE_SID pid is set.
> > 
> > [akpm@linux-foundation.org: coding-style fixes]
> > Signed-off-by: Scott James Remnant <scott@ubuntu.com>
> > Acked-by: Matt Helsley <matthltc@us.ibm.com>
> > Cc: Oleg Nesterov <oleg@tv-sign.ru>
> > Cc: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
> > Cc: "David S. Miller" <davem@davemloft.net>
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> 
> Acked-by: David S. Miller <davem@davemloft.net>

Ta.

> This is more process handling level stuff than actual networking
> or connector bits, so it should probably be merged via akpm's
> usual patch bombs or some other relevant tree.
> 
> Andrew, if you really want, I can take this into net-next-2.6

No probs, I'll send it for 2.6.32-rc1.