Quoting Sukadev Bhattiprolu (sukadev@xxxxxxxxxxxxxxxxxx):
>
> >From a1fdec1036a952359d02a7c667d126bd2fff6804 Mon Sep 17 00:00:00 2001
> From: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxxxxxxx>
Acked-by: Serge Hallyn <serue@xxxxxxxxxx>
> ---
> 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;
>
> --
> 1.5.2.5
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