[Devel] Re: [PATCH 0/6] /proc/pid/checkpointable

[Oren Laadan]

Serge E. Hallyn wrote:
> Quoting Oren Laadan (orenl at cs.columbia.edu):
>>
>> Serge E. Hallyn wrote:
>>> Quoting Oren Laadan (orenl at cs.columbia.edu):
>>>> Sukadev Bhattiprolu wrote:
>>>>> From: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
>>>>> Date: Fri, 13 Mar 2009 17:25:42 -0700
>>>>> Subject: [PATCH 5/6] Define and use proc_pid_checkpointable()
>>>>>
>>>>> Create a proc file, /proc/pid/checkpointable, which shows '1' if
>>>>> task is checkpointable and '0' if it is not.
>>>>>
>>>>> To determine whether a task is checkpointable, the handler for this
>>>>> new proc file, shares the same code with sys_checkpoint().
>>> Hey Oren,
>>>
>>> 3 counter-points:
>>>
>>>> I still don't understand why we would like to do it this way.
>>>>
>>>> First, it makes little sense to do it per-task, because we are supposed
>>>> to checkpoint an entire container.
>>> Yes we need per-container info too.  Actually, per-checkpoint-job-init,
>>> so if we send pids in for that, it should return false if we send in the
>>> pid of a task which isn't a proper checkpoint-job-init.
>>>
>>> But we also want the info per-task, for debugging info.
>>>
>> My suggestions works for this two: we add a flag CR_CTX_DRYRUN; a task
>> can ask to checkpoint itself, or another task, with CR_CTX_DRYRUN and
>> the checkpoint code runs without actual effect. (If we don't want to
>> expose the actual flag to userspace, then we simply use it in an
>> implementation of a /proc/PID/checkpointable operation).
> 
> Hmm, so if we pass in CR_CTX_DRYRUN, then the fd can point to a file
> wherein to store a text represenation of the reason?
> 
> Dave will probably hate it, but it could be worse...

Either that.

Or continue using a debugfs interface, except that the  implementation
will go through an internal interface as I suggest.

Or spit the reason on the kernel console so the user can check dmesg
for it (like when 'modprobe' fails).

Oren.
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