/*
* Generic net pointers are to be used by modules to put some private
* stuff on the struct net without explicit struct net modification
*
* The rules are simple:
* 1. set pernet_operations->id. After register_pernet_device you
* will have the id of your private pointer.
* 2. set pernet_operations->size to have the code allocate and free
* a private structure pointed to from struct net.
* 3. do not change this pointer while the net is alive;
* 4. do not try to have any private reference on the net_generic object.
*
* After accomplishing all of the above, the private pointer can be
* accessed with the net_generic() call.
*/
struct net_generic {
union {
struct {
unsigned int len;
struct rcu_head rcu;
} s;
void *ptr[0];
};
};
static inline void *net_generic(const struct net *net, unsigned int id)
{
struct net_generic *ng;
void *ptr;
rcu_read_lock();
ng = rcu_dereference(net->gen);
ptr = ng->ptr[id];
rcu_read_unlock();
return ptr;
}
➠ example
lib/librte_eal/linuxapp/kni/kni_misc.c
static int kni_net_id;
struct kni_net {
unsigned long device_in_use; /* device in use flag */
struct mutex kni_kthread_lock;
struct task_struct *kni_kthread;
struct rw_semaphore kni_list_lock;
struct list_head kni_list_head;
};
static struct pernet_operations kni_net_ops = {
.init = kni_init_net,
.exit = kni_exit_net,
#ifdef HAVE_SIMPLIFIED_PERNET_OPERATIONS
.id = &kni_net_id,
.size = sizeof(struct kni_net),
#endif
static int __init
kni_init(void){
...
rc = register_pernet_subsys(&kni_net_ops);
...
}
static int
kni_open(struct inode *inode, struct file *file)
{
struct net *net = current->nsproxy->net_ns;
struct kni_net *knet = net_generic(net, kni_net_id);
...
}
include/net/net_namespace.h
struct pernet_operations {
struct list_head list;
int (*init)(struct net *net);
void (*exit)(struct net *net);
void (*exit_batch)(struct list_head *net_exit_list);
unsigned int *id;
size_t size;
};
net/core/net_namespace.c
/**
* register_pernet_subsys - register a network namespace subsystem
* @ops: pernet operations structure for the subsystem
*
* Register a subsystem which has init and exit functions
* that are called when network namespaces are created and
* destroyed respectively.
*
* When registered all network namespace init functions are
* called for every existing network namespace. Allowing kernel
* modules to have a race free view of the set of network namespaces.
*
* When a new network namespace is created all of the init
* methods are called in the order in which they were registered.
*
* When a network namespace is destroyed all of the exit methods
* are called in the reverse of the order with which they were
* registered.
*/
int register_pernet_subsys(struct pernet_operations *ops)
{
int error;
mutex_lock(&net_mutex);
error = register_pernet_operations(first_device, ops);
mutex_unlock(&net_mutex);
return error;
}
EXPORT_SYMBOL_GPL(register_pernet_subsys);
