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author | Pavel Emelyanov <xemul@openvz.org> | 2008-04-15 07:36:08 (GMT) |
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committer | David S. Miller <davem@davemloft.net> | 2008-04-15 07:36:08 (GMT) |
commit | dec827d174d7f76c457238800183ca864a639365 (patch) | |
tree | ca7c04e35eda9956afef94678a2a863c3e75e2ed /include/net/netns | |
parent | c93cf61fd1d5378134f9b06703f7078067542e00 (diff) | |
download | linux-fsl-qoriq-dec827d174d7f76c457238800183ca864a639365.tar.xz |
[NETNS]: The generic per-net pointers.
Add the elastic array of void * pointer to the struct net.
The access rules are simple:
1. register the ops with register_pernet_gen_device to get
the id of your private pointer
2. call net_assign_generic() to put the private data on the
struct net (most preferably this should be done in the
->init callback of the ops registered)
3. do not store any private reference on the net_generic array;
4. do not change this pointer while the net is alive;
5. use the net_generic() to get the pointer.
When adding a new pointer, I copy the old array, replace it
with a new one and schedule the old for kfree after an RCU
grace period.
Since the net_generic explores the net->gen array inside rcu
read section and once set the net->gen->ptr[x] pointer never
changes, this grants us a safe access to generic pointers.
Quoting Paul: "... RCU is protecting -only- the net_generic
structure that net_generic() is traversing, and the [pointer]
returned by net_generic() is protected by a reference counter
in the upper-level struct net."
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/netns')
-rw-r--r-- | include/net/netns/generic.h | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/include/net/netns/generic.h b/include/net/netns/generic.h new file mode 100644 index 0000000..0c04fd2 --- /dev/null +++ b/include/net/netns/generic.h @@ -0,0 +1,49 @@ +/* + * generic net pointers + */ + +#ifndef __NET_GENERIC_H__ +#define __NET_GENERIC_H__ + +#include <linux/rcupdate.h> + +/* + * 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. register the ops with register_pernet_gen_device to get the id + * of your private pointer; + * 2. call net_assign_generic() to put the private data on the struct + * net (most preferably this should be done in the ->init callback + * of the ops registered); + * 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 { + unsigned int len; + struct rcu_head rcu; + + void *ptr[0]; +}; + +static inline void *net_generic(struct net *net, int id) +{ + struct net_generic *ng; + void *ptr; + + rcu_read_lock(); + ng = rcu_dereference(net->gen); + BUG_ON(id == 0 || id > ng->len); + ptr = ng->ptr[id - 1]; + rcu_read_unlock(); + + return ptr; +} + +extern int net_assign_generic(struct net *net, int id, void *data); +#endif |