[PATCH v7 0/2] ns, procfs: pid conversion between ns and showing pidns hierarchy

[Chen Hanxiao]

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
Ex:
     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
pid:[4026532388]

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.

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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1.9.3