[resend][PATCH v9 0/3] 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 checkpoint/restore

  We could know whether two pids had relationship
  between each other.

      init_pid_ns 1
            │
   ┌────────────┐
  ns1                       ns2
   │                        │
  200                       300
                             │
                            ns2
                             │
                            400

  #cat /proc/pidns_hierarchy
  200 1 1
  300 1 1
  400 300 2

2. useful 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.

v9: fix codes be inluded if CONFIG_PID_NS=n
    add docs to describe the usage of pidns_hierarchy procfs
v8: fix some improper comments
    use max() from kernel.h
v7: change pidns_hierarchy style 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, replacing 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 (3):
  procfs: show hierarchy of pid namespace
  /proc/PID/status: show all sets of pid according to ns
  Documentation: add docs for /proc/pidns_hierarchy

 Documentation/namespaces/pidns-hierarchy.txt |  51 +++++
 fs/proc/Kconfig                              |   6 +
 fs/proc/Makefile                             |   1 +
 fs/proc/array.c                              |  16 ++
 fs/proc/internal.h                           |   9 +
 fs/proc/pidns_hierarchy.c                    | 280 +++++++++++++++++++++++++++
 fs/proc/root.c                               |   1 +
 7 files changed, 364 insertions(+)
 create mode 100644 Documentation/namespaces/pidns-hierarchy.txt
 create mode 100644 fs/proc/pidns_hierarchy.c

-- 
1.9.3