[PATCH 2/6] c/r: [pty 1/2] allow allocation of desired pty slave

Oren Laadan orenl at librato.com
Fri Sep 4 09:08:32 PDT 2009

Serge E. Hallyn wrote:
> Quoting Oren Laadan (orenl at librato.com):
>> During restart, we need to allocate pty slaves with the same
>> identifiers as recorded during checkpoint. Modify the allocation code
>> to allow an in-kernel caller to request a specific slave identifier.
>> For this, add a new field to task_struct - 'required_id'. It will
>> hold the desired identifier when restoring a (master) pty.
>> The code in ptmx_open() will use this value only for tasks that try to
>> open /dev/ptmx that are restarting (PF_RESTARTING), and if the value
>> isn't CKPT_REQUIRED_NONE (-1).
> So noone has indicated any preference for this versus the ptmx_create()
> approach...
> I'm satisfied knowing we have a working fallback in case task->required_id
> is deemed unacceptable.
> However I'd like to not have linux-kernel folks think us morons for not
> having considered that.  Can you add a message to the changelog saying
> why we're going with this approach (namely, that it lets us re-use
> filp_open() instead of having to do a custom alloc_file in a new code-path,
> which introduces maintenance duplication for file permission checking
> paths)?

Good point, will add.


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