Subject: Re: [PATCH net-next 2/7] net: rtnetlink: allow only one idx saving stats attribute

From: Roopa Prabhu <[email-masked]>
Date: Wed, 27 Apr 2016 22:18:33 -0700

On 4/27/16, 9:18 AM, Nikolay Aleksandrov wrote:
> We can't allow more than one stats attribute which uses the local idx
> since the result will be a mess. This is a simple check to make sure
> only one is being used at a time. Later when the filter_mask's 32 bits
> are over we can switch to a bitmap.
>
> Signed-off-by: Nikolay Aleksandrov <[email-masked]>
> ---
>  include/net/rtnetlink.h |  6 ++++++
>  net/core/rtnetlink.c    | 17 +++++++++++++++--
>  2 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
> index 2f87c1ba13de..3f3b0b1b8722 100644
> --- a/include/net/rtnetlink.h
> +++ b/include/net/rtnetlink.h
> @@ -150,4 +150,10 @@ int rtnl_nla_parse_ifla(struct nlattr **tb, const struct nlattr *head, int len);
>  
>  #define MODULE_ALIAS_RTNL_LINK(kind) MODULE_ALIAS("rtnl-link-" kind)
>  
> +/* at most one attribute which can save a local idx is allowed to be set
> + * IFLA_STATS_IDX_ATTR_MASK has all the idx saving attributes set and is
> + * used to check if more than one is being requested
> + */
> +#define IFLA_STATS_IDX_ATTR_MASK 0
> +
>  #endif
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index aeb2fa9b1cda..ea03b6cd3d3c 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -3512,7 +3512,7 @@ static int rtnl_stats_get(struct sk_buff *skb, struct nlmsghdr *nlh)
>  	struct if_stats_msg *ifsm;
>  	struct net_device *dev = NULL;
>  	struct sk_buff *nskb;
> -	u32 filter_mask;
> +	u32 filter_mask, lidx_filter;
>  	int lidx = 0;
>  	int err;
>  
> @@ -3529,6 +3529,14 @@ static int rtnl_stats_get(struct sk_buff *skb, struct nlmsghdr *nlh)
>  	if (!filter_mask)
>  		return -EINVAL;
>  
> +	/* only one attribute which can save a local idx is allowed at a time
> +	 * even though rtnl_stats_get doesn't save the lidx, we need to be
> +	 * consistent with the dump side and error out
> +	 */
> +	lidx_filter = filter_mask & IFLA_STATS_IDX_ATTR_MASK;
> +	if (lidx_filter && !is_power_of_2(lidx_filter))
> +		return -EINVAL;
> +
>  	nskb = nlmsg_new(if_nlmsg_stats_size(dev, filter_mask), GFP_KERNEL);
>  	if (!nskb)
>  		return -ENOBUFS;
> @@ -3556,7 +3564,7 @@ static int rtnl_stats_dump(struct sk_buff *skb, struct netlink_callback *cb)
>  	struct net_device *dev;
>  	struct hlist_head *head;
>  	unsigned int flags = NLM_F_MULTI;
> -	u32 filter_mask = 0;
> +	u32 filter_mask = 0, lidx_filter;
>  	int err;
>  
>  	s_h = cb->args[0];
> @@ -3570,6 +3578,11 @@ static int rtnl_stats_dump(struct sk_buff *skb, struct netlink_callback *cb)
>  	if (!filter_mask)
>  		return -EINVAL;
>  
> +	/* only one attribute which can save a local idx is allowed at a time */
> +	lidx_filter = filter_mask & IFLA_STATS_IDX_ATTR_MASK;
> +	if (lidx_filter && !is_power_of_2(lidx_filter))
> +		return -EINVAL;
> +
>  	
instead of introducing the restriction at this level, is it possible to use two args for this
like below and avoid the restriction ?
cb->args[2] = current filter being processed
cb->args[3] = private filter idx (your lidx)