The patch titled
prctl: add PR_{SET,GET}_CHILD_REAPER to allow simple process supervision
has been added to the -mm tree. Its filename is
prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision.patch
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------------------------------------------------------
Subject: prctl: add PR_{SET,GET}_CHILD_REAPER to allow simple process supervision
From: Lennart Poettering <lennart@xxxxxxxxxxxxxx>
Userspace service managers/supervisors need to track their started
services. Many services daemonize by double-forking and get implicitely
re-parented to PID 1. The process manager will no longer be able to
receive the SIGCHLD signals for them.
With this prctl, a service manager can mark itself as a sort of 'sub-init'
process, able to stay as the parent process for all processes created by
the started services. All SIGCHLD signals will be delivered to the
service manager.
As a side effect, the relevant parent PID information does not get lost by
a double-fork, which results in a more elaborate process tree and 'ps'
output.
This is orthogonal to PID namespaces. PID namespaces are isolated from
each other, while a service management process usually requires the
serices to live in the same namespace, to be able to talk to each other.
Users of this will be the systemd per-user instance, which provides
init-like functionality for the user's login session and D-Bus, which
activates bus services on on-demand. Both will need init-like
capabilities to be able to properly keep track of the services they start.
Signed-off-by: Lennart Poettering <lennart@xxxxxxxxxxxxxx>
Signed-off-by: Kay Sievers <kay.sievers@xxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: <linux-man@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/prctl.h | 3 +++
include/linux/sched.h | 2 ++
kernel/exit.c | 9 ++++++++-
kernel/fork.c | 2 ++
kernel/sys.c | 7 +++++++
5 files changed, 22 insertions(+), 1 deletion(-)
diff -puN include/linux/prctl.h~prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision include/linux/prctl.h
--- a/include/linux/prctl.h~prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision
+++ a/include/linux/prctl.h
@@ -102,4 +102,7 @@
#define PR_MCE_KILL_GET 34
+#define PR_SET_CHILD_REAPER 35
+#define PR_GET_CHILD_REAPER 36
+
#endif /* _LINUX_PRCTL_H */
diff -puN include/linux/sched.h~prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision include/linux/sched.h
--- a/include/linux/sched.h~prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision
+++ a/include/linux/sched.h
@@ -1296,6 +1296,8 @@ struct task_struct {
* execve */
unsigned in_iowait:1;
+ /* Reparent child processes to this process instead of pid 1. */
+ unsigned child_reaper:1;
/* Revert to default priority/policy when forking */
unsigned sched_reset_on_fork:1;
diff -puN kernel/exit.c~prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision kernel/exit.c
--- a/kernel/exit.c~prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision
+++ a/kernel/exit.c
@@ -701,7 +701,7 @@ static struct task_struct *find_new_reap
__acquires(&tasklist_lock)
{
struct pid_namespace *pid_ns = task_active_pid_ns(father);
- struct task_struct *thread;
+ struct task_struct *thread, *reaper;
thread = father;
while_each_thread(father, thread) {
@@ -712,6 +712,13 @@ static struct task_struct *find_new_reap
return thread;
}
+ /* find the first ancestor which is marked as child_reaper */
+ for (reaper = father->parent;
+ reaper != &init_task && reaper != pid_ns->child_reaper;
+ reaper = reaper->parent)
+ if (reaper->child_reaper)
+ return reaper;
+
if (unlikely(pid_ns->child_reaper == father)) {
write_unlock_irq(&tasklist_lock);
if (unlikely(pid_ns == &init_pid_ns))
diff -puN kernel/fork.c~prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision kernel/fork.c
--- a/kernel/fork.c~prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision
+++ a/kernel/fork.c
@@ -1328,6 +1328,8 @@ static struct task_struct *copy_process(
p->parent_exec_id = current->self_exec_id;
}
+ p->child_reaper = 0;
+
spin_lock(¤t->sighand->siglock);
/*
diff -puN kernel/sys.c~prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision kernel/sys.c
--- a/kernel/sys.c~prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision
+++ a/kernel/sys.c
@@ -1800,6 +1800,13 @@ SYSCALL_DEFINE5(prctl, int, option, unsi
else
error = PR_MCE_KILL_DEFAULT;
break;
+ case PR_SET_CHILD_REAPER:
+ me->child_reaper = !!arg2;
+ error = 0;
+ break;
+ case PR_GET_CHILD_REAPER:
+ error = put_user(me->child_reaper, (int __user *) arg2);
+ break;
default:
error = -EINVAL;
break;
_
Patches currently in -mm which might be from lennart@xxxxxxxxxxxxxx are
prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision.patch
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