Eric W. Biederman wrote:
> I finally found a chance to review the pid namespace implementation in
> detail and currently it is much to easy to find issues where the
> kernel does the wrong thing outside of the initial pid namespace.
> At the same time the pid namespace code we have does appear
> to be a good base to build on.
> 
> Therefore until the dust settles and we are certain we have the
> ABI and the implementation as correct as humanly possible let's
> hide the availability of process ID namespaces behind
> CONFIG_EXPERIMENTAL.

Sorry for the late answer - I was out for a conference and the
organization committee didn't provide an internet access.

I currently have a set of patches that move all the namespaces
cloning code under the config option. This is done to help
embedded people have a small kernel.

I was planning to wait with this set untill 2.6.24-rc-mm1 kernel,
but since (as I see) this is required rather badly I will send this
set in a couple of days.

Thanks,
Pavel

> Allowing users to avoid bugs, and removing a guarantee of bug
> compatibility.  Allowing any issues that may be found to
> be fixed properly.
> 
> If CONFIG_PID_NS=N this patch will cause copy_pid_ns to
> unconditionally return -EINVAL removing the availability
> of multiple pid namespaces.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> ---
>  init/Kconfig |   12 ++++++++++++
>  kernel/pid.c |    4 ++++
>  2 files changed, 16 insertions(+), 0 deletions(-)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 8b88d0b..72e37c0 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -215,6 +215,18 @@ config USER_NS
>  	  vservers, to use user namespaces to provide different
>  	  user info for different servers.  If unsure, say N.
>  
> +config PID_NS
> +	bool "PID Namespaces (EXPERIMENTAL)"
> +	default n
> +	depends on EXPERIMENTAL
> +	help
> +	  Suport process id namespaces.  This allows having multiple
> +	  process with the same pid as long as they are in different
> +	  pid namespaces.  This is a building block of containers.
> +
> +	  Unless you want to work with an experimental feature
> +	  say N here.
> +
>  config AUDIT
>  	bool "Auditing support"
>  	depends on NET
> diff --git a/kernel/pid.c b/kernel/pid.c
> index d1db36b..8a5637b 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -599,6 +599,10 @@ struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *old
>  	if (flags & CLONE_THREAD)
>  		goto out_put;
>  
> +#ifndef CONFIG_PID_NS
> +	goto out_put;
> +#endif
> +
>  	new_ns = create_pid_namespace(old_ns->level + 1);
>  	if (!IS_ERR(new_ns))
>  		new_ns->parent = get_pid_ns(old_ns);

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