Re: [PATCH] proc connector: add event for process becoming session leader

[Scott James Remnant <scott@ubuntu.com>]

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On Mon, 2009-06-22 at 16:19 -0700, Andrew Morton wrote:

> Let's cc the Process Events developer..
> 
Ah great, thanks - I couldn't find an e-mail address.

> On Mon, 15 Jun 2009 13:03:08 +0100
> Scott James Remnant <scott@ubuntu.com> wrote:
> 
> > 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.
> > 
> 
> hm, well, I don't have much useful to say about the overall idea, but
> it seems to slot into the existing code simply enough.
> 
> > ---
> >  drivers/connector/cn_proc.c |   25 +++++++++++++++++++++++++
> >  include/linux/cn_proc.h     |   10 ++++++++++
> >  kernel/exit.c               |    4 +++-
> >  3 files changed, 38 insertions(+), 1 deletions(-)
> 
> We seem to have forgotten to document this entire interface, so I can't
> ding you for forgetting to update the forgotten documentation.
> 
> > diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
> > index c5afc98..7d48cd9 100644
> > --- a/drivers/connector/cn_proc.c
> > +++ b/drivers/connector/cn_proc.c
> > @@ -139,6 +139,31 @@ void proc_id_connector(struct task_struct *task, int which_id)
> >  	cn_netlink_send(msg, CN_IDX_PROC, GFP_KERNEL);
> >  }
> >  
> > +void proc_sid_connector(struct task_struct *task)
> 
> It would be nice to have a nice comment explaining what this function
> does.  Ditto all the others in there, really.
> 
> > +{
> > +	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;
> 
> Please pass all patches through scripts/checkpatch.pl.
> 
> > +	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;
> 
> This is a bit of a worry.  In a containerised environment, pids are not
> unique.  Now what do we do?
> 
I must admit, that I just copy and pasted the existing functions - bugs
and all :-)

> > +	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 --git a/include/linux/cn_proc.h b/include/linux/cn_proc.h
> > index b8125b2..47dac5e 100644
> > --- a/include/linux/cn_proc.h
> > +++ b/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(struct task_struct *task,
> >  				     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 --git a/kernel/exit.c b/kernel/exit.c
> > index b6c90b5..5162589 100644
> > --- a/kernel/exit.c
> > +++ b/kernel/exit.c
> > @@ -360,8 +360,10 @@ 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);
> 

Scott
-- 
Scott James Remnant
scott@ubuntu.com

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