[Devel] [PATCH 08/17] Pid-NS(V3) Define/use pid->upid_list list.

[Pavel Emelianov]

sukadev at us.ibm.com wrote:
> Subject: [PATCH 08/17] Pid-NS(V3) Define/use pid->upid_list list.
> 
> From: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> 
> 
> With multiple pid namespaces, a process would be known by several pid_t
> values, one in each pid namespace. To represent this, we introduce a
> 'struct upid' which associates a single pid_t value with a single pid
> namespace.
> 
> We then replace the pid->nr field in 'struct pid' with a list of struct upid'
> entries (referred to as 'pid->upid_list'). This list represents the multiple
> pid_t values of the process, one in each namespace. The current patch adds
> just one element to this list, corresponding to 'init_pid_ns'. Subsequent
> patches implement multiple pid namespaces and add more elements to the list.
> 
> The 'struct upid' also replaces 'struct pid' in the pid_hash table to enable us
> to find processes given a pid_t from any namespace (i.e we find 'struct upid'
> for a given pid_t and from the 'struct upid', we find the 'struct pid' of the
> process)
> 
> We finally reimplement find_pid() and pid_to_nr() to use pid->upid_list
> and remove unused fields from 'struct pid'.
> 
> Changelog:
> 	2.6.21-mm2-pidns3:
> 
> 	- 'struct upid' used to be called 'struct pid_nr' and a list of these
> 	   were hanging off of 'struct pid'. So, we renamed 'struct pid_nr'
> 	   and now hold them in a statically sized array in 'struct pid' since
> 	   the number of 'struct upid's for a process is known at process-
> 	   creation time.
> 	  
> 	2.6.21-rc3-mm2:
> 
> 	- [Eric Biederman] Combine all logical changes into one patch
> 	- [Eric Biederman] Implement __pid_nr(pid_ns, pid) for use in procfs.
> 	  (now called pid_to_nr_in_ns()).
> 	- [Serge Hallyn]: Remove (!pid_nr) check in free_pid_nr()
> 
> Signed-off-by: Cedric Le Goater <clg at fr.ibm.com>
> Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> ---
>  fs/proc/array.c               |   30 ++++++--
>  fs/proc/base.c                |    9 ++
>  include/linux/init_task.h     |   14 +++-
>  include/linux/pid.h           |   62 ++++++++++++++---
>  include/linux/pid_namespace.h |   15 ++++
>  kernel/fork.c                 |    2 
>  kernel/pid.c                  |  145 +++++++++++++++++++++++++++++++++---------
>  7 files changed, 220 insertions(+), 57 deletions(-)
> 
> Index: lx26-22-rc4-mm2/include/linux/pid.h
> ===================================================================
> --- lx26-22-rc4-mm2.orig/include/linux/pid.h	2007-06-15 18:44:50.000000000 -0700
> +++ lx26-22-rc4-mm2/include/linux/pid.h	2007-06-15 19:47:58.000000000 -0700
> @@ -16,6 +16,25 @@ enum pid_type
>  	PIDTYPE_MAX
>  };
>  
> +struct pid_namespace;
> +
> +/*
> + * A struct upid holds a process identifier (or pid->nr) for a given
> + * pid namespace.
> + *
> + * A list of 'struct upid' entries is stored in the struct pid. This list
> + * is used to get the process identifier associated with the pid
> + * namespace it is being seen from.
> + */
> +struct upid
> +{
> +	/* Try to keep pid_chain in the same cacheline as nr for find_pid */
> +	struct hlist_node pid_chain; 	/* link hash collisions on pid_hash */
> +	int nr;	 			/* user space pid number */
> +	struct pid_namespace *pid_ns; 	/* pid namespace in which nr is valid */
> +	struct pid *pid; 		/* back to task's unique kernel pid */
> +};
> +
>  /*
>   * What is struct pid?
>   *
> @@ -48,12 +67,11 @@ enum pid_type
>  struct pid
>  {
>  	atomic_t count;
> -	/* Try to keep pid_chain in the same cacheline as nr for find_pid */
> -	int nr;
> -	struct hlist_node pid_chain;
>  	/* lists of tasks that use this pid */
>  	struct hlist_head tasks[PIDTYPE_MAX];
>  	struct rcu_head rcu;
> +	int num_upids;
> +	struct upid upid_list[1];

Further in your patches you define MAX_NESTED_PID_NS. What for, you
use the linked list here!?

>  };
>  
>  extern struct pid init_struct_pid;

[snip]
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