Subject: Re: [PATCH net-next] net: rtnetlink: add rx_otherhost_dropped for struct rtnl_link_stats

From: "Yajun Deng" <[email-masked]>
Date: Fri, 08 Jul 2022 07:43:00 +0000

July 8, 2022 3:03 PM, "Eric Dumazet" <[email-masked]> wrote:

> On Fri, Jul 8, 2022 at 8:33 AM Yajun Deng <[email-masked]> wrote:
> 
>> The commit 794c24e9921f ("net-core: rx_otherhost_dropped to core_stats")
>> introduce rx_otherhost_dropped, add rx_otherhost_dropped for struct
>> rtnl_link_stats to keep sync with struct rtnl_link_stats64.
>> 
>> As the same time, add BUILD_BUG_ON() in copy_rtnl_link_stats().
> 
> Any reason you chose to not cc the original patch author ?
> 
Sorry for that, I'll do it later.

> If I remember well, not adding fields into legacy 'struct
> rtnl_link_stats' was a conscious decision.
> 
> There is no requirement to keep rtnl_link_stats & rtnl_link_stats64 in sync.
> rtnl_link_stats is deprecated, user space really wants to use
> rtnl_link_stats64 instead,
> if they need access to new fields added in recent kernels.
> 
Got it. Thanks.

> Thank you.
> 
> [1]
> commit 9256645af09807bc52fa8b2e66ecd28ab25318c4
> Author: Jarod Wilson <[email-masked]>
> Date: Mon Feb 1 18:51:04 2016 -0500
> 
> net/core: relax BUILD_BUG_ON in netdev_stats_to_stats64
> 
> The netdev_stats_to_stats64 function copies the deprecated
> net_device_stats format stats into rtnl_link_stats64 for legacy support
> purposes, but with the BUILD_BUG_ON as it was, it wasn't possible to
> extend rtnl_link_stats64 without also extending net_device_stats. Relax
> the BUILD_BUG_ON to only require that rtnl_link_stats64 is larger, and
> zero out all the stat counters that aren't present in net_device_stats.
> 
> CC: Eric Dumazet <[email-masked]>
> CC: [email-masked]
> Signed-off-by: Jarod Wilson <[email-masked]>
> Signed-off-by: David S. Miller <[email-masked]>
> 
>> Signed-off-by: Yajun Deng <[email-masked]>
>> ---
>> include/uapi/linux/if_link.h | 1 +
>> net/core/rtnetlink.c | 36 +++++++-----------------------------
>> 2 files changed, 8 insertions(+), 29 deletions(-)
>> 
>> diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
>> index e36d9d2c65a7..fd6776d665c8 100644
>> --- a/include/uapi/linux/if_link.h
>> +++ b/include/uapi/linux/if_link.h
>> @@ -37,6 +37,7 @@ struct rtnl_link_stats {
>> __u32 tx_compressed;
>> 
>> __u32 rx_nohandler;
>> + __u32 rx_otherhost_dropped;
>> };
>> 
>> /**
>> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
>> index ac45328607f7..818649850b2c 100644
>> --- a/net/core/rtnetlink.c
>> +++ b/net/core/rtnetlink.c
>> @@ -908,35 +908,13 @@ static unsigned int rtnl_dev_combine_flags(const struct net_device *dev,
>> static void copy_rtnl_link_stats(struct rtnl_link_stats *a,
>> const struct rtnl_link_stats64 *b)
>> {
>> - a->rx_packets = b->rx_packets;
>> - a->tx_packets = b->tx_packets;
>> - a->rx_bytes = b->rx_bytes;
>> - a->tx_bytes = b->tx_bytes;
>> - a->rx_errors = b->rx_errors;
>> - a->tx_errors = b->tx_errors;
>> - a->rx_dropped = b->rx_dropped;
>> - a->tx_dropped = b->tx_dropped;
>> -
>> - a->multicast = b->multicast;
>> - a->collisions = b->collisions;
>> -
>> - a->rx_length_errors = b->rx_length_errors;
>> - a->rx_over_errors = b->rx_over_errors;
>> - a->rx_crc_errors = b->rx_crc_errors;
>> - a->rx_frame_errors = b->rx_frame_errors;
>> - a->rx_fifo_errors = b->rx_fifo_errors;
>> - a->rx_missed_errors = b->rx_missed_errors;
>> -
>> - a->tx_aborted_errors = b->tx_aborted_errors;
>> - a->tx_carrier_errors = b->tx_carrier_errors;
>> - a->tx_fifo_errors = b->tx_fifo_errors;
>> - a->tx_heartbeat_errors = b->tx_heartbeat_errors;
>> - a->tx_window_errors = b->tx_window_errors;
>> -
>> - a->rx_compressed = b->rx_compressed;
>> - a->tx_compressed = b->tx_compressed;
>> -
>> - a->rx_nohandler = b->rx_nohandler;
>> + size_t i, n = sizeof(*b) / sizeof(u64);
>> + const u64 *src = (const u64 *)b;
>> + u32 *dst = (u32 *)a;
>> +
>> + BUILD_BUG_ON(n != sizeof(*a) / sizeof(u32));
>> + for (i = 0; i < n; i++)
>> + dst[i] = src[i];
>> }
>> 
>> /* All VF info */
>> --
>> 2.25.1