On Mon, 13 Apr 2009 10:42:02 +0200
Jiri Pirko <jpi...@redhat.com> wrote:

> This patch introduces a new list in struct net_device and brings a set of
> functions to handle the work with device address list. The list is a 
> replacement
> for the original dev_addr field and because in some situations there is need 
> to
> carry several device addresses with the net device. To be backward compatible,
> dev_addr is made to point to the first member of the list so original drivers
> sees no difference.
> 
> Signed-off-by: Jiri Pirko <jpi...@redhat.com>
> ---
>  include/linux/netdevice.h |   51 +++++++++-
>  net/core/dev.c            |  264 
> +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 313 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index ff8db51..8cf62f1 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -210,6 +210,12 @@ struct dev_addr_list
>  #define dmi_users    da_users
>  #define dmi_gusers   da_gusers
>  
> +struct hw_addr {
> +     struct list_head        list;
> +     unsigned char           addr[MAX_ADDR_LEN];
> +     int                     refcount;
> +};
> +
>  struct hh_cache
>  {
>       struct hh_cache *hh_next;       /* Next entry                        */
> @@ -776,8 +782,12 @@ struct net_device
>   */
>       unsigned long           last_rx;        /* Time of last Rx      */
>       /* Interface address info used in eth_type_trans() */
> -     unsigned char           dev_addr[MAX_ADDR_LEN]; /* hw address, (before 
> bcast
> -                                                        because most packets 
> are unicast) */
> +     unsigned char           *dev_addr;      /* hw address, (before bcast
> +                                                because most packets are
> +                                                unicast) */
> +
> +     struct list_head        dev_addr_list; /* list of device hw addresses */
> +     spinlock_t              dev_addr_list_lock;
>  
>       unsigned char           broadcast[MAX_ADDR_LEN];        /* hw bcast add 
> */
>  
> @@ -1779,6 +1789,32 @@ static inline void netif_addr_unlock_bh(struct 
> net_device *dev)
>       spin_unlock_bh(&dev->addr_list_lock);
>  }
>  
> +/* Locking helpers for spinlock guarding dev_addr_list */
> +
> +static inline void netif_dev_addr_lock(struct net_device *dev)
> +{
> +     spin_lock(&dev->dev_addr_list_lock);
> +}
> +
> +static inline void netif_dev_addr_lock_bh(struct net_device *dev)
> +{
> +     spin_lock_bh(&dev->dev_addr_list_lock);
> +}
> +
> +static inline void netif_dev_addr_unlock(struct net_device *dev)
> +{
> +     spin_unlock(&dev->dev_addr_list_lock);
> +}
> +
> +static inline void netif_dev_addr_unlock_bh(struct net_device *dev)
> +{
> +     spin_unlock_bh(&dev->dev_addr_list_lock);
> +}
> +

This lock is unnecessary, use RCU list for read.
Since all changes are under RTNL mutex, there is no chance
for conflict on update.
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