path: root/Documentation
diff options
authorCyrill Gorcunov <gorcunov@openvz.org>2012-05-31 16:26:43 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-31 17:49:32 -0700
commit818411616baf46ceba0cff6f05af3a9b294734f7 (patch)
treeb6e338e20d4a45b6a05ffa37e6af33e0cc1b50c0 /Documentation
parentsysctl: make kernel.ns_last_pid control dependent on CHECKPOINT_RESTORE (diff)
fs, proc: introduce /proc/<pid>/task/<tid>/children entry
When we do checkpoint of a task we need to know the list of children the task, has but there is no easy and fast way to generate reverse parent->children chain from arbitrary <pid> (while a parent pid is provided in "PPid" field of /proc/<pid>/status). So instead of walking over all pids in the system (creating one big process tree in memory, just to figure out which children a task has) -- we add explicit /proc/<pid>/task/<tid>/children entry, because the kernel already has this kind of information but it is not yet exported. This is a first level children, not the whole process tree. Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: Pavel Emelyanov <xemul@parallels.com> Cc: Serge Hallyn <serge.hallyn@canonical.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 912af6ce5626..d8d3f9a8e5a3 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -40,6 +40,7 @@ Table of Contents
3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
3.5 /proc/<pid>/mountinfo - Information about mounts
3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
+ 3.7 /proc/<pid>/task/<tid>/children - Information about task children
4 Configuring procfs
4.1 Mount options
@@ -1578,6 +1579,23 @@ then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
comm value.
+3.7 /proc/<pid>/task/<tid>/children - Information about task children
+This file provides a fast way to retrieve first level children pids
+of a task pointed by <pid>/<tid> pair. The format is a space separated
+stream of pids.
+Note the "first level" here -- if a child has own children they will
+not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
+to obtain the descendants.
+Since this interface is intended to be fast and cheap it doesn't
+guarantee to provide precise results and some children might be
+skipped, especially if they've exited right after we printed their
+pids, so one need to either stop or freeze processes being inspected
+if precise results are needed.
Configuring procfs