Eric W. Biederman wrote:
> This patch allows you to create a new network namespace
> using sys_clone, or sys_unshare.
> 
> As the network namespace is still experimental and under development
> clone and unshare support is only made available when CONFIG_NET_NS is
> selected at compile time.
> 
> As this patch introduces network namespace support into code paths
> that exist when the CONFIG_NET is not selected there are a few
> additions made to net_namespace.h to allow a few more functions
> to be used when the networking stack is not compiled in.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> ---
>  include/linux/sched.h       |    1 +
>  include/net/net_namespace.h |   18 ++++++++++++++++++
>  kernel/fork.c               |    3 ++-
>  kernel/nsproxy.c            |   15 +++++++++++++--
>  net/Kconfig                 |    8 ++++++++
>  net/core/net_namespace.c    |   43 +++++++++++++++++++++++++++++++++++++++++--
>  6 files changed, 83 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index a01ac6d..e10a0a8 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -27,6 +27,7 @@
>  #define CLONE_NEWUTS		0x04000000	/* New utsname group? */
>  #define CLONE_NEWIPC		0x08000000	/* New ipcs */
>  #define CLONE_NEWUSER		0x10000000	/* New user namespace */
> +#define CLONE_NEWNET		0x20000000	/* New network namespace */

This new flag is going to conflict with the pid namespace flag 
CLONE_NEWPID in -mm. It might be worth changing it to:

#define CLONE_NEWNET		0x40000000

The changes in nxproxy.c and fork.c will also conflict but I don't 
think we can do much about it for now.

C. 

>  /*
>   * Scheduling policies
> diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
> index ac8f830..3ea4194 100644
> --- a/include/net/net_namespace.h
> +++ b/include/net/net_namespace.h
> @@ -38,11 +38,23 @@ extern struct net init_net;
> 
>  extern struct list_head net_namespace_list;
> 
> +#ifdef CONFIG_NET
> +extern struct net *copy_net_ns(unsigned long flags, struct net *net_ns);
> +#else
> +static inline struct net *copy_net_ns(unsigned long flags, struct net *net_ns)
> +{
> +	/* There is nothing to copy so this is a noop */
> +	return net_ns;
> +}
> +#endif
> +
>  extern void __put_net(struct net *net);
> 
>  static inline struct net *get_net(struct net *net)
>  {
> +#ifdef CONFIG_NET
>  	atomic_inc(&net->count);
> +#endif
>  	return net;
>  }
> 
> @@ -60,19 +72,25 @@ static inline struct net *maybe_get_net(struct net *net)
> 
>  static inline void put_net(struct net *net)
>  {
> +#ifdef CONFIG_NET
>  	if (atomic_dec_and_test(&net->count))
>  		__put_net(net);
> +#endif
>  }
> 
>  static inline struct net *hold_net(struct net *net)
>  {
> +#ifdef CONFIG_NET
>  	atomic_inc(&net->use_count);
> +#endif
>  	return net;
>  }
> 
>  static inline void release_net(struct net *net)
>  {
> +#ifdef CONFIG_NET
>  	atomic_dec(&net->use_count);
> +#endif
>  }
> 
>  extern void net_lock(void);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 33f12f4..5e67f90 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1608,7 +1608,8 @@ asmlinkage long sys_unshare(unsigned long unshare_flags)
>  	err = -EINVAL;
>  	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
>  				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
> -				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER))
> +				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER|
> +				CLONE_NEWNET))
>  		goto bad_unshare_out;
> 
>  	if ((err = unshare_thread(unshare_flags)))
> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index a4fb7d4..f1decd2 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -20,6 +20,7 @@
>  #include <linux/mnt_namespace.h>
>  #include <linux/utsname.h>
>  #include <linux/pid_namespace.h>
> +#include <net/net_namespace.h>
> 
>  static struct kmem_cache *nsproxy_cachep;
> 
> @@ -98,8 +99,17 @@ static struct nsproxy *create_new_namespaces(unsigned long flags,
>  		goto out_user;
>  	}
> 
> +	new_nsp->net_ns = copy_net_ns(flags, tsk->nsproxy->net_ns);
> +	if (IS_ERR(new_nsp->net_ns)) {
> +		err = PTR_ERR(new_nsp->net_ns);
> +		goto out_net;
> +	}
> +
>  	return new_nsp;
> 
> +out_net:
> +	if (new_nsp->user_ns)
> +		put_user_ns(new_nsp->user_ns);
>  out_user:
>  	if (new_nsp->pid_ns)
>  		put_pid_ns(new_nsp->pid_ns);
> @@ -132,7 +142,7 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
> 
>  	get_nsproxy(old_ns);
> 
> -	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWUSER)))
> +	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | CLONE_NEWUSER | CLONE_NEWNET)))
>  		return 0;
> 
>  	if (!capable(CAP_SYS_ADMIN)) {
> @@ -164,6 +174,7 @@ void free_nsproxy(struct nsproxy *ns)
>  		put_pid_ns(ns->pid_ns);
>  	if (ns->user_ns)
>  		put_user_ns(ns->user_ns);
> +	put_net(ns->net_ns);
>  	kmem_cache_free(nsproxy_cachep, ns);
>  }
> 
> @@ -177,7 +188,7 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
>  	int err = 0;
> 
>  	if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
> -			       CLONE_NEWUSER)))
> +			       CLONE_NEWUSER | CLONE_NEWNET)))
>  		return 0;
> 
>  	if (!capable(CAP_SYS_ADMIN))
> diff --git a/net/Kconfig b/net/Kconfig
> index cdba08c..ab4e6da 100644
> --- a/net/Kconfig
> +++ b/net/Kconfig
> @@ -27,6 +27,14 @@ if NET
> 
>  menu "Networking options"
> 
> +config NET_NS
> +	bool "Network namespace support"
> +	default n
> +	depends on EXPERIMENTAL && !SYSFS
> +	help
> +	  Allow user space to create what appear to be multiple instances
> +	  of the network stack.
> +
>  source "net/packet/Kconfig"
>  source "net/unix/Kconfig"
>  source "net/xfrm/Kconfig"
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index 0e6cb02..e478e35 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -4,6 +4,7 @@
>  #include <linux/slab.h>
>  #include <linux/list.h>
>  #include <linux/delay.h>
> +#include <linux/sched.h>
>  #include <net/net_namespace.h>
> 
>  /*
> @@ -32,12 +33,10 @@ void net_unlock(void)
>  	mutex_unlock(&net_list_mutex);
>  }
> 
> -#if 0
>  static struct net *net_alloc(void)
>  {
>  	return kmem_cache_alloc(net_cachep, GFP_KERNEL);
>  }
> -#endif
> 
>  static void net_free(struct net *net)
>  {
> @@ -128,6 +127,46 @@ out_undo:
>  	goto out;
>  }
> 
> +struct net *copy_net_ns(unsigned long flags, struct net *old_net)
> +{
> +	struct net *new_net = NULL;
> +	int err;
> +
> +	get_net(old_net);
> +
> +	if (!(flags & CLONE_NEWNET))
> +		return old_net;
> +
> +#ifndef CONFIG_NET_NS
> +	return ERR_PTR(-EINVAL);
> +#endif
> +
> +	err = -ENOMEM;
> +	new_net = net_alloc();
> +	if (!new_net)
> +		goto out;
> +
> +	mutex_lock(&net_mutex);
> +	err = setup_net(new_net);
> +	if (err)
> +		goto out_unlock;
> +
> +	net_lock();
> +	list_add_tail(&new_net->list, &net_namespace_list);
> +	net_unlock();
> +
> +
> +out_unlock:
> +	mutex_unlock(&net_mutex);
> +out:
> +	put_net(old_net);
> +	if (err) {
> +		net_free(new_net);
> +		new_net = ERR_PTR(err);
> +	}
> +	return new_net;
> +}
> +
>  static int __init net_ns_init(void)
>  {
>  	int err;

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