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 Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ 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 -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html