[PATCH v8 0/2] ns, procfs: pid conversion between ns and showing pidns hierarchy

From: Chen Hanxiao
Date: Tue Nov 18 2014 - 04:31:24 EST

This series will expose pid inside containers
via procfs.
Also show the hierarchy of pid namespcae.
Then we could know how pid looks inside a container
and their ns relationships.

1. helpful for nested container check/restore
>From /proc/PID/ns/pid, we could know whether two pid lived
in the same ns.
>From this patch, we could know whether two pid had relationship
between each other.

2. used for pid translation from container
init_pid_ns ns1 ns2
t1 2
t2 `- 3 1
t3 `- 4 3
t4 `- 5 `- 5 1
t5 `- 6 `- 8 3

It could solve problems like: we see a pid 3 goes wrong
in container's log, what is its pid on hosts:
a) inside container:
# readlink /proc/3/ns/pid

b) on host:
We show it in the form of :
<init_PID> <parent_of_init_PID> <relative PID level>

# cat /proc/pidns_hierarchy
14918 1 1
16263 14918 2
16581 1 1
Then we could easily find /proc/16263/ns/pid->4026532388.
On host, we knew that reported pid 3 is in level 2,
and its parental pid ns is from pid 14918.

c) on host, check child of 16263, grep it from status:
NSpid: 16268 8 3

We knew that pid 16268 is pid 3 reported by container.

v8: fix some improper comments
use max() from kernel.h
v7: change stype to be consistent with current interface like
<init_PID> <parent_of_init_PID> <relative PID level>
remove EXPERT dependent in Kconfig
v6: fix some get_pid leaks and do some cleanups
v5: collect pid by find_ge_pid;
use local list inside nslist_proc_show;
use get_pid, remove mutex lock.
v4: simplify pid collection and some performance optimizamtion
fix another race issue.
v3: fix a race issue and memory leak issue in pidns_hierarchy;
add another two fielsd: NSpgid and NSsid.
v2: use a procfs text file instead of dirs under /proc for
showing pidns hierarchy;
add two new fields: NStgid and NSpid
keep fields of Tgid and Pid unchanged for back compatibility.

Chen Hanxiao (2):
procfs: show hierarchy of pid namespace
/proc/PID/status: show all sets of pid according to ns

fs/proc/Kconfig | 6 +
fs/proc/Makefile | 1 +
fs/proc/array.c | 17 +++
fs/proc/pidns_hierarchy.c | 280 ++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 304 insertions(+)
create mode 100644 fs/proc/pidns_hierarchy.c


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