[RFC][PATCH 3/7][v2] Add target_pid parameter to alloc_pidmap()

[Oren Laadan]

Sukadev Bhattiprolu wrote:
> From a1fdec1036a952359d02a7c667d126bd2fff6804 Mon Sep 17 00:00:00 2001
> From: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
> Date: Mon, 4 May 2009 01:17:41 -0700
> Subject: [RFC][PATCH 3/7][v2] Add target_pid parameter to alloc_pidmap()
> 
> With support for setting a specific pid number for a process,
> alloc_pidmap() will need a paramter a 'target_pid' parameter.
> 
> Changelog[v2]:
> 	- (Serge Hallyn) Check for 'pid < 0' in set_pidmap().(Code
> 	  actually checks for 'pid <= 0' for completeness).
> 
> Signed-off-by: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
> ---

Reviewed-by: Oren Laadan <orenl at cs.columbia.edu>


>  kernel/pid.c |   28 ++++++++++++++++++++++++++--
>  1 files changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/pid.c b/kernel/pid.c
> index b2d6a19..b44dd21 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -147,11 +147,35 @@ static int alloc_pidmap_page(struct pidmap *map)
>  	return 0;
>  }
>  
> -static int alloc_pidmap(struct pid_namespace *pid_ns)
> +static int set_pidmap(struct pid_namespace *pid_ns, int pid)
> +{
> +	int offset;
> +	struct pidmap *map;
> +
> +	if (pid <= 0 || pid >= pid_max)
> +		return -EINVAL;
> +
> +	offset = pid & BITS_PER_PAGE_MASK;
> +	map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
> +
> +	if (alloc_pidmap_page(map))
> +		return -ENOMEM;
> +
> +	if (test_and_set_bit(offset, map->page))
> +		return -EBUSY;
> +
> +	atomic_dec(&map->nr_free);
> +	return pid;
> +}
> +
> +static int alloc_pidmap(struct pid_namespace *pid_ns, int target_pid)
>  {
>  	int i, rc, offset, max_scan, pid, last = pid_ns->last_pid;
>  	struct pidmap *map;
>  
> +	if (target_pid)
> +		return set_pidmap(pid_ns, target_pid);
> +
>  	pid = last + 1;
>  	if (pid >= pid_max)
>  		pid = RESERVED_PIDS;
> @@ -270,7 +294,7 @@ struct pid *alloc_pid(struct pid_namespace *ns)
>  
>  	tmp = ns;
>  	for (i = ns->level; i >= 0; i--) {
> -		nr = alloc_pidmap(tmp);
> +		nr = alloc_pidmap(tmp, 0);
>  		if (nr < 0)
>  			goto out_free;
>