Subject: Re: [PATCH net-next 1/2] rtnetlink: add new RTM_GETSTATS message to dump link stats

From: roopa <[email-masked]>
Date: Mon, 14 Mar 2016 23:30:30 -0700

On 3/14/16, 8:00 AM, Nicolas Dichtel wrote:
> Le 13/03/2016 02:56, Roopa Prabhu a écrit :
>> From: Roopa Prabhu <[email-masked]>
>>
>> This patch adds a new RTM_GETSTATS message to query link stats via netlink
>> from the kernel. RTM_NEWLINK also dumps stats today, but RTM_NEWLINK
>> returns a lot more than just stats and is expensive in some cases when
>> frequent polling for stats from userspace is a common operation.
>>
>> RTM_GETSTATS is an attempt to provide a light weight netlink message
>> to explicity query only link stats from the kernel on an interface.
>> The idea is to also keep it extensible so that new kinds of stats can be
>> added to it in the future.
>>
>> This patch adds the following attribute for NETDEV stats:
>> struct nla_policy ifla_stats_policy[IFLA_STATS_MAX + 1] = {
>>          [IFLA_STATS_LINK64]  = { .len = sizeof(struct rtnl_link_stats64) },
>> };
>>
>> This patch also allows for af family stats (an example af stats for IPV6
>> is available with the second patch in the series).
>>
>> Like any other rtnetlink message, RTM_GETSTATS can be used to get stats of
>> a single interface or all interfaces with NLM_F_DUMP.
>>
>> Future possible new types of stat attributes:
>> - IFLA_MPLS_STATS  (nested. for mpls/mdev stats)
>> - IFLA_EXTENDED_STATS (nested. extended software netdev stats like bridge,
>>    vlan, vxlan etc)
>> - IFLA_EXTENDED_HW_STATS (nested. extended hardware stats which are
>>    available via ethtool today)
>>
>> This patch also declares a filter mask for all stat attributes.
>> User has to provide a mask of stats attributes to query. This will be
>> specified in a new hdr 'struct if_stats_msg' for stats messages.
>>
>> Without any attributes in the filter_mask, no stats will be returned.
>>
>> This patch has been tested with modified iproute2 ifstat.
>>
>> Suggested-by: Jamal Hadi Salim <[email-masked]>
>> Signed-off-by: Roopa Prabhu <[email-masked]>
> [snip]
>> diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
>> index 249eef9..0840f3e 100644
>> --- a/include/uapi/linux/if_link.h
>> +++ b/include/uapi/linux/if_link.h
> [snip]
>> +enum {
>> +    IFLA_STATS_UNSPEC,
>> +    IFLA_STATS_LINK64,
>> +    IFLA_STATS_INET6,
> IFLA_STATS_INET6 is part on patch #2, it's not used in this patch.
yep, will fix it
>
>> +    __IFLA_STATS_MAX,
>> +};
>> +
>> +#define IFLA_STATS_MAX (__IFLA_STATS_MAX - 1)
>> +
>> +#define IFLA_STATS_FILTER_BIT(ATTR)    (1 << (ATTR))
>> +
>>   #endif /* _UAPI_LINUX_IF_LINK_H */
>> diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
>> index ca764b5..2bbb300 100644
>> --- a/include/uapi/linux/rtnetlink.h
>> +++ b/include/uapi/linux/rtnetlink.h
>> @@ -139,6 +139,13 @@ enum {
>>       RTM_GETNSID = 90,
>>   #define RTM_GETNSID RTM_GETNSID
>>
>> +    RTM_NEWSTATS = 92,
>> +#define RTM_NEWSTATS RTM_NEWSTATS
>> +    RTM_DELSTATS = 93,
>> +#define RTM_DELSTATS RTM_DELSTATS
> RTM_DELSTATS is never used.

yeah, i had to define it just because rtnetlink_rcv_msg seems to expect all three to be
there when it tries to check if it is a get msg. But, i could sure not declare this
but make rtnetlink_rcv_msg happy by keeping the GET msg at the right offset.
>
>> +    RTM_GETSTATS = 94,
>> +#define RTM_GETSTATS RTM_GETSTATS
>> +
>>       __RTM_MAX,
>>   #define RTM_MAX        (((__RTM_MAX + 3) & ~3) - 1)
>>   };
>> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
>> index d2d9e5e..d1e3d17 100644
>> --- a/net/core/rtnetlink.c
>> +++ b/net/core/rtnetlink.c
> [snip]
>> +static noinline size_t if_nlmsg_stats_size(const struct net_device *dev,
>> +                       u32 filter_mask)
> Why are you using the 'noinline' attribute?

I actually picked it up from if_nlmsg_size ...

>
>> +{
>> +    size_t size = 0;
>> +
>> +    if (filter_mask & IFLA_STATS_FILTER_BIT(IFLA_STATS_LINK64))
>> +        size += nla_total_size(sizeof(struct rtnl_link_stats64));
>> +
>> +    size += rtnl_link_get_af_stats_size(dev, filter_mask);
>> +
>> +    return size;
>> +}
>