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Date:   Fri, 9 Sep 2016 16:39:12 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Cc:     Jiri Pirko <jiri@...nulli.us>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>, nogahf@...lanox.com,
        idosch@...lanox.com, eladr@...lanox.com, yotamg@...lanox.com,
        ogerlitz@...lanox.com, roopa@...ulusnetworks.com,
        linville@...driver.com, tgraf@...g.ch, gospo@...ulusnetworks.com,
        sfeldma@...il.com, sd@...asysnail.net, eranbe@...lanox.com,
        ast@...mgrid.com, edumazet@...gle.com, hannes@...essinduktion.org,
        f.fainelli@...il.com, dsa@...ulusnetworks.com
Subject: Re: [patch net-next v8 2/3] net: core: Add offload stats to if_stats_msg


> On Sep 9, 2016, at 4:36 PM, Nikolay Aleksandrov <nikolay@...ulusnetworks.com> wrote:
> 
>> 
>> On Sep 8, 2016, at 9:19 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>> 
>> From: Nogah Frankel <nogahf@...lanox.com>
>> 
>> Add a nested attribute of offload stats to if_stats_msg
>> named IFLA_STATS_LINK_OFFLOAD_XSTATS.
>> Under it, add SW stats, meaning stats only per packets that went via
>> slowpath to the cpu, named IFLA_OFFLOAD_XSTATS_CPU_HIT.
>> 
>> Signed-off-by: Nogah Frankel <nogahf@...lanox.com>
>> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
>> ---
>> include/uapi/linux/if_link.h |  9 ++++
>> net/core/rtnetlink.c         | 97 ++++++++++++++++++++++++++++++++++++++++++--
>> 2 files changed, 102 insertions(+), 4 deletions(-)
>> 
> [snip]
>> @@ -3655,6 +3725,22 @@ static int rtnl_fill_statsinfo(struct sk_buff *skb, struct net_device *dev,
>> 		}
>> 	}
>> 
>> +	if (stats_attr_valid(filter_mask, IFLA_STATS_LINK_OFFLOAD_XSTATS,
>> +			     *idxattr)) {
>> +		attr = nla_nest_start(skb, IFLA_STATS_LINK_OFFLOAD_XSTATS);
>> +		if (!attr)
>> +			goto nla_put_failure;
>> +
>> +		err = rtnl_get_offload_stats(skb, dev);
>> +		if (err == -ENODATA)
>> +			nla_nest_cancel(skb, attr);
>> +		else
>> +			nla_nest_end(skb, attr);
>> +
>> +		if ((err) && (err != -ENODATA))
>> +			goto nla_put_failure;
>> +	}
>> +
> 
> Hmm, actually on a second read I think there’s a potential problem here. Since you don’t set *idxattr and if the space
> isn’t enough the dump will get restarted and this will lead to an infinite loop.

Err, poor choice of words. I meant the loop will be for userspace since the dump will err out at the same spot all the time so it
won’t be able to ever finish. :-)

> I.e. if the previous attributes filled the skb and there’s not enough room for this one, it will return an error
> but *idxattr will be == 0 from the previous attribute thus the whole dump will be restarted (this is in case someone
> requests this attribute with some of the others of course).
> 
> Cheers,
> Nik
> 
> 
>> 	nlmsg_end(skb, nlh);
>> 
>> 	return 0;
>> @@ -3712,6 +3798,9 @@ static size_t if_nlmsg_stats_size(const struct net_device *dev,
>> 		}
>> 	}
>> 
>> +	if (stats_attr_valid(filter_mask, IFLA_STATS_LINK_OFFLOAD_XSTATS, 0))
>> +		size += rtnl_get_offload_stats_size(dev);
>> +
>> 	return size;
>> }
>> 
>> -- 
>> 2.5.5

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