[CRIU] pstree C/R problems

[Huang Qiang]

On 2012/9/27 19:03, Pavel Emelyanov wrote:
> On 09/27/2012 11:59 AM, Huang Qiang wrote:
>> 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?
> 
> The plan is -- by default we should reject dumping a process tree if there's a session
> in a tree whose leader is not taken into a dump. But there should be a special case in

If we really need that default, maybe we need more prompt for the usage, because
we don't have a CRIU tool for the users to run their programs, so I think my usage
is common and reasonable, and crtools should work for that, isn't it?

> crtools (Cyrill is working on it) when we explicitly dump that state and on restore
> let the tree inherit any sid from crtools.
> 

Agreed with this solution.

> Does this decision suit you?
> 

Yes, thanks, and would you please talk about my second question?

>> 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
>>
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>>
> 
> 
> .
>