[RFC][PATCH 0/4] Object creation with a pre-defined id (v2)

[Oren Laadan]

On Fri, 28 Mar 2008, Nadia.Derbey at bull.net wrote:

>
> Hi,
>
> Here is a second version of what has been proposed 2 weeks ago to create
> an object with a pre-defined id (this feature would be used during the
> restart operation) - see thread https://lists.linux-foundation.org/pipermail/containers/2008-March/thread.html#10287
>
> Main changes since last version:
>  . Pavel's suggestion has been integrated; this makes things more readable:
>    alloc_pidmap() is unchanged and a alloc_fixed_pidmap() is added for the
>    predefined ids.
>  . Oren's suggestion has been integrated:
>    We now have a single file under /proc/self (/proc/self/next_id).
>    When this file is filled, a structure pointed to by the calling task struct
>    is filled with the id(s).
>    Then, when the object is created, the id(s) present in that structure are
>    used, instead of the default ones.
>    The syntax is one of:
>      . echo "LONG XX" > /proc/self/next_id
>        next object to be created will have an id set to XX
>      . echo "LONG<n> X0 ... X<n-1>" > /proc/self/next_id
>        next object to be created will have its ids set to XX0, ... X<n-1>
>        This is particularly useful for processes that may have several ids
>        if they belong to nested namespaces.

I suggest that there be a way for the process to reset its task->next_id
discarding previous settings, e.g. to recover from an error condition and
prevent subsuquent syscalls from using the task->next_id unintentionally. 
Something like "echo RESET > /proc/self/next_id" (or s/RESET/0/ ... etc).

Oren.

> The objects covered here are ipc objects and processes.
>
> The patches are still against 2.6.25-rc3-mm1, in the following order:
>
> [PATCH 1/4] adds the procfs facility for next object to be created, this
>            object being associated to a single id.
> [PATCH 2/4] enhances the procfs facility for objects associated to multiple
>            ids (like processes).
> [PATCH 3/4] makes use of the specified id (if any) to allocate the new IPC
>            object (changes the ipc_addid() path).
> [PATCH 4/4] uses the specified id(s) (if any) to set the upid nr(s) for a newly
>            allocated process (changes the alloc_pid() path).
>
> Any comment and/or suggestions are welcome.
>
> Regards,
> Nadia
>
> --
>