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| author | Cyrill Gorcunov <gorcunov@openvz.org> | 2012-05-31 16:26:43 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-05-31 17:49:32 -0700 |
| commit | 818411616baf46ceba0cff6f05af3a9b294734f7 (patch) | |
| tree | b6e338e20d4a45b6a05ffa37e6af33e0cc1b50c0 /Documentation | |
| parent | 98ed57eef9f67dfe541be0bca34660ffc88365b2 (diff) | |
| download | lwn-818411616baf46ceba0cff6f05af3a9b294734f7.tar.gz lwn-818411616baf46ceba0cff6f05af3a9b294734f7.zip | |
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')
| -rw-r--r-- | Documentation/filesystems/proc.txt | 18 |
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 ------------------------------------------------------------------------------ |