[Devel] Re: [RFC][PATCH 2.6.22-rc5] System V IPC: new IPC_SETID command to modify an ID

[Daniel Lezcano]

Kirill Korotaev wrote:
> Cedric Le Goater wrote:
>> Pierre Peiffer wrote:
>>
>>
>>> This patch adds a new IPC_SETID command to the System V IPCs set of
>>> commands, which allows to change the ID of an existing IPC.
>>>
>>> This command can be used through the semctl/shmctl/msgctl API, with the new
>>> ID passed as the third argument for msgctl and shmctl (instead of a
>>> pointer) and through the fourth argument for semctl.
>>>
>>> To be successful, the following rules must be respected:
>>> - the IPC exists
>>> - the user must be allowed to change the IPC attributes regarding the IPC
>>>  permissions.
>>> - the new ID must satisfy the ID computation rule.
>>> - the entry (in the kernel internal table of IPCs) corresponding to the new
>>>  ID must be free.
>>
>> That's an interesting way to reset the ids of sysv ipcs during a restart (after 
>> a checkpoint) and we're looking for ways to do that among other things.
>>
>> How does it fit openvz ? Is it something openvz could use ? 
> 
> my personal imho is that we should not export such interfaces to user space
> and do the checkpointing from the kernel.
> 
> it simplifies a lot of things and makes checkpointing more elegant.
> So until there is some user-space usage scenario of the patch I missed -
> i wouldn't commit it.

Hi Kirill,

I have no particular preference about checkpointing from userspace or 
kernelspace. Can you explain why doing the checkpoint from kernel 
simplifies the problem ? Do you have some examples about resources 
checkpointed from kernel which make the job easier ?

I thought we can divide system into subsystem and use the generic 
netlink to define a family for each subsystem. The result will be a 
checkpoint orchestrated from userspace but checkpointed from kernel.

   -- Daniel

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