Subject: Re: [PATCH] phonet netlink: allow multiple messages per skb in route dump

From: Rémi Denis-Courmont <[email-masked]>
Date: Mon, 19 Jan 2015 22:11:50 +0200

Le lundi 19 janvier 2015, 12:15:24 Johannes Berg a écrit :
> From: Johannes Berg <[email-masked]>
> 
> My previous patch to this file changed the code to be bug-compatible
> towards userspace. Unless userspace (which I wasn't able to find)
> implements the dump reader by hand in a wrong way, this isn't needed.

The canonical userspace is there (specifically src/pnroute.c):
https://gitorious.org/meego-cellular/phonet-utils/

AFAICT, it should work either way. By now, I expect what's left of the 
Maemo/Meego/Mer/whatever community has forked or rewritten it though.

> If it uses libnl or similar code putting multiple messages into a
> single SKB is far more efficient.
> 
> Change the code to do this. While at it, also clean it up and don't
> use so many variables - just store the address in the callback args
> directly.
> 
> Signed-off-by: Johannes Berg <[email-masked]>
> ---
>  net/phonet/pn_netlink.c | 22 +++++++---------------
>  1 file changed, 7 insertions(+), 15 deletions(-)
> 
> diff --git a/net/phonet/pn_netlink.c b/net/phonet/pn_netlink.c
> index 54d766842c2b..bc5ee5fbe6ae 100644
> --- a/net/phonet/pn_netlink.c
> +++ b/net/phonet/pn_netlink.c
> @@ -272,31 +272,23 @@ static int route_doit(struct sk_buff *skb, struct
> nlmsghdr *nlh) static int route_dumpit(struct sk_buff *skb, struct
> netlink_callback *cb) {
>  	struct net *net = sock_net(skb->sk);
> -	u8 addr, addr_idx = 0, addr_start_idx = cb->args[0];
> +	u8 addr;
> 
>  	rcu_read_lock();
> -	for (addr = 0; addr < 64; addr++) {
> -		struct net_device *dev;
> +	for (addr = cb->args[0]; addr < 64; addr++) {
> +		struct net_device *dev = phonet_route_get_rcu(net, addr << 2);
> 
> -		dev = phonet_route_get_rcu(net, addr << 2);
>  		if (!dev)
>  			continue;
> 
> -		if (addr_idx++ < addr_start_idx)
> -			continue;
> -		fill_route(skb, dev, addr << 2, NETLINK_CB(cb->skb).portid,
> -			   cb->nlh->nlmsg_seq, RTM_NEWROUTE);
> -		/* fill_route() used to return > 0 (or negative errors) but
> -		 * never 0 - ignore the return value and just go out to
> -		 * call dumpit again from outside to preserve the behavior
> -		 */
> -		goto out;
> +		if (fill_route(skb, dev, addr << 2, NETLINK_CB(cb->skb).portid,
> +			       cb->nlh->nlmsg_seq, RTM_NEWROUTE) < 0)
> +			goto out;
>  	}
> 
>  out:
>  	rcu_read_unlock();
> -	cb->args[0] = addr_idx;
> -	cb->args[1] = 0;
> +	cb->args[0] = addr;
> 
>  	return skb->len;
>  }

-- 
Rémi