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Subject[PATCH v9 3/3] Documentation: add docs for /proc/pidns_hierarchy
Date
Signed-off-by: Chen Hanxiao <chenhanxiao@cn.fujitsu.com>
---
Documentation/namespaces/pidns-hierarchy.txt | 51 ++++++++++++++++++++++++++++
1 file changed, 51 insertions(+)
create mode 100644 Documentation/namespaces/pidns-hierarchy.txt

diff --git a/Documentation/namespaces/pidns-hierarchy.txt b/Documentation/namespaces/pidns-hierarchy.txt
new file mode 100644
index 0000000..1820ae6d
--- /dev/null
+++ b/Documentation/namespaces/pidns-hierarchy.txt
@@ -0,0 +1,51 @@
+This document is about how to use pid namespace hierarchy procfs.
+
+We knew whether two pids living in the same pid namespace
+by /proc/PID/ns/pid, but their relationships
+between pids were unknown:
+we couldn't tell that one pid was another one's parent/siblings...
+But /proc/pidns_hierarchy could tell us the answer.
+
+/proc/pidns_hierarchy will show the hierarchy of pid namespace
+in the form of:
+
+<init_PID> <parent_of_init_PID> <relative PID level>
+
+init_PID: child reaper in a pid namespace
+parent_of_init_PID: init_PID's parent, child reaper too
+relative PID level: pid level relative to caller's ns,
+ started from '1'.
+
+Here is a chart to describe the relationship between
+some pids:
+
+ init_pid_ns level 0
+ |
+ 1
+ |
+┌────────────┐
+ns1 ns2 level 1
+| |
+1550 18060
+ |
+ |
+ ns3 level 2
+ |
+ 18102
+ |
+ ┌──────────┐
+ ns4 ns5 level 3
+ | |
+ 1534 1600
+
+It will be showed by /proc/pidns_hierarchy as below:
+
+#cat /proc/pidns_hierarchy
+18060 1 1
+18102 18060 2
+1534 18102 3
+1600 18102 3
+1550 1 1
+
+Note: numbers in column 1 are pid numbers in current ns,
+ they represent the pid '1' in different ns
--
1.9.3


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