Re: [RFC V2 PATCH] rtnetlink: Add method to calculate dump info data size

[Eric Dumazet <eric.dumazet@gmail.com>]

Le lundi 09 mai 2011 à 15:26 -0700, Greg Rose a écrit :
> The message size allocated for rtnl info dumps was limited to a single
> page.  This is not enough for additional interface info available with
> devices that support SR-IOV.  Calculate the amount of data required so
> the dump can allocate enough data to satisfy the request.
> 
> V2 of this patch adds a new argument to the rtnl_register service that
> allows for a new method to calculate the amount of data required to
> complete the info dump request.  So far the method is only implemented
> for the RTM_GETLINK slot.
> 
> Signed-off-by: Greg Rose <gregory.v.rose@intel.com>

>  
> +static u16 rtnl_calcit(struct sk_buff *skb)
> +{
> +	struct net *net = sock_net(skb->sk);
> +	int h;
> +	int idx = 0, s_idx;
> +	struct net_device *dev;
> +	struct hlist_head *head;
> +	struct hlist_node *node;
> +	u16 alloc_size = 0;
> +
> +	for (h = 0; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
> +		idx = 0;
> +		head = &net->dev_index_head[h];
> +		hlist_for_each_entry(dev, node, head, index_hlist) {
> +			if (idx < s_idx) {
> +				idx++;
> +				continue;
> +			}
> +			alloc_size = (u16)if_nlmsg_size(dev);
> +			break;
> +		}
> +	}
> +
> +	return alloc_size;
> +}
> +


Sorry this wont scale. Some machines have thousand of devices.

Just make an upper approximation, you dont need an exact one ;)