[Devel] Re: [PATCH RFC linux-cr] add rpid to ckpt_pids struct

[Matt Helsley]

On Tue, Mar 09, 2010 at 03:04:51PM -0600, Serge E. Hallyn wrote:
> When we restart an application, we won't try to restore the original
> pid in the parent pid_ns, so we don't checkpoint that pid.
> 
> However, if we are going to dump mount info from userspace using
> /proc/pid/mountinfo, then it will be easiest for a restart wrapper
> to use the pids from the checkpoint image.  So add rpid to the
> pids info we dump.
> 
> The rpid is taken as the vpid in the checkpointer's pidnamespace.
> The container may not have valid pids in the checkpointer's
> pid namespace, in which case the rpid will be 0, and the checkpoint
> wrapper will not be able to access the mountinfo.

This seems like a good idea to me.

Acked-by: Matt Helsley <matthltc at us.ibm.com>

> 
> Note that eventually, in order to restore nested pid namespaces,
> we will need to change our approach again, so as to print out
> the pid in every ancestor pid_ns.

Perhaps we should think about what will be needed so we can avoid
extra checkpoint image format changes? Or perhaps there's something
we can do right now to ease any future transition at least?

> Signed-off-by: Serge E. Hallyn <serue at us.ibm.com>
> ---
>  checkpoint/checkpoint.c        |    6 ++++--
>  include/linux/checkpoint_hdr.h |    1 +
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c
> index b3c1c4f..c9b5966 100644
> --- a/checkpoint/checkpoint.c
> +++ b/checkpoint/checkpoint.c
> @@ -329,13 +329,15 @@ static int checkpoint_pids(struct ckpt_ctx *ctx)
>  		for (n = 0; n < min(nr_tasks, CKPT_HDR_PIDS_CHUNK); n++) {
>  			task = tasks_arr[pos];
> 
> +			h[n].rpid = task_pid_vnr(task);
>  			h[n].vpid = task_pid_nr_ns(task, ns);
>  			h[n].vtgid = task_tgid_nr_ns(task, ns);
>  			h[n].vpgid = task_pgrp_nr_ns(task, ns);
>  			h[n].vsid = task_session_nr_ns(task, ns);
>  			h[n].vppid = task_tgid_nr_ns(task->real_parent, ns);
> -			ckpt_debug("task[%d]: vpid %d vtgid %d parent %d\n",
> -				   pos, h[n].vpid, h[n].vtgid, h[n].vppid);
> +			ckpt_debug("task[%d]: rpid %d vpid %d vtgid %d "
> +				"parent %d\n", pos, h[n].rpid, h[n].vpid,
> +				h[n].vtgid, h[n].vppid);
>  			pos++;
>  		}
>  		rcu_read_unlock();
> diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
> index 41412d1..d3fff0b 100644
> --- a/include/linux/checkpoint_hdr.h
> +++ b/include/linux/checkpoint_hdr.h
> @@ -327,6 +327,7 @@ struct ckpt_hdr_tree {
>  } __attribute__((aligned(8)));
> 
>  struct ckpt_pids {
> +	__s32 rpid; /* pid in checkpointer's pidns */

e.g. Perhaps stick it at the end of the previously-defined pids.

>  	__s32 vpid;
>  	__s32 vppid;
>  	__s32 vtgid;

Cheers,
	-Matt Helsley
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