[CRIU] pstree C/R problems

[Huang Qiang]

HI:
I use a simple code to test CRIU, when it runs, the ids seem like this:

UID        PID  PPID  PGID   SID  C STIME TTY          TIME   CMD
root     11988  9904 11988 11988  0 10:37 ?        00:00:00     sshd: root at pts/3
root     11996 11988 11996 11996  0 10:37 pts/3    00:00:00       -bash
root     12056 11996 12056 11996  0 10:38 pts/3    00:00:00         ./multitask_simple
root     12057 12056 12056 11996  0 10:38 pts/3    00:00:00           ./multitask_simple

then I run:
# ./crtools dump -D /home/hq/image -t 12056
it is successful.

then restore it:
# ./crtools restore -D /home/hq/image -t 12056
I got error:
 12057: Error (cr-restore.c:677): Requested sid 11996 doesn't match inherited 11952
 12056: Error (cr-restore.c:633): 12057 exited, status=1
Error (cr-restore.c:911): Someone can't be restored


I read the pstree C/R code, and found that it didn't handle the situation that
the root task is not the session leader. But if there is only one task in the tree,
C/R can successful, otherwise, will face the error.

Is this a bug? Or is CRIU has a limitation right now for the root task?
And what's your plan for this situation?
I think we may also need a helper for root task, of course have other things to consider.

BTW, the born_sid mechanism seems didn't do any really work for rebuild the pstree,
but for the check. We may neither support the tree like this:
        pid = 5
        sid = 5
           /
          /
      pid = 7
      sid = 6
         /
        /
    pid = 9
    sid = 8

Right?

Since I didn't find any scheme for the the problems I mentioned above in the TODO
list, if you guys have any plan or thoughts, could you share them here?
And maybe I can help to do this work.


regards.
Huang Qiang