From: Jamal Hadi Salim <jhs@mojatatu•com>
To: David Miller <davem@davemloft•net>, eric.dumazet@gmail•com
Cc: stephen@networkplumber•org, jarod@redhat•com,
linux-kernel@vger•kernel.org, edumazet@google•com,
jiri@mellanox•com, daniel@iogearbox•net, tom@herbertland•com,
j.vosburgh@gmail•com, vfalico@gmail•com,
gospo@cumulusnetworks•com, netdev@vger•kernel.org
Subject: Re: [PATCH net v3 2/4] net: add rx_nohandler stat counter
Date: Tue, 9 Feb 2016 05:56:28 -0500 [thread overview]
Message-ID: <56B9C5DC.4050505@mojatatu.com> (raw)
In-Reply-To: <20160209.034023.50018877443465909.davem@davemloft.net>
On 16-02-09 03:40 AM, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@gmail•com>
> Date: Mon, 08 Feb 2016 14:57:40 -0800
>
>> Whole point of TLV is that it allows us to add new fields at the end of
>> the structures.
> ...
>> Look at iproute2, you were the one adding in 2004 code to cope with
>> various tcp_info sizes.
>>
>> So 12 years later, you cannot say it does not work anymore.
>
> +1
>
The TLV L should be canonical way to determine length. i.e should be
sufficient to just look at L and understand that content has changed.
But:
Using sizeof could be dangerous unless the data is packed to be
32-bit aligned. Looking INET_DIAG_INFO check for sizeof
there is a small 8 bit hole in tcp_info I think between
these two fields:
----
__u8 tcpi_snd_wscale : 4, tcpi_rcv_wscale : 4;
__u32 tcpi_rto;
---
The kernel will pad to make sure the TLV data is 32-bit aligned.
I am not sure if that will be the same length as sizeof() in all
hardware + compilers... For this case,
it is almost safe to just add a version field - probably in the hole.
Or have a #define to say what the expected length should be. Or add
an 8 bit pad.
In general adding new fields that are non-optional is problematic. i.e
by non-optional i mean always expected to be present.
I think a good test is old kernel with new iproute2. If the new field
is non-optional, it will fail (example iproute2 may try to print a value
that it expects but because old kernel doesnt understand it; it is
non-existent).
cheers,
jamal
next prev parent reply other threads:[~2016-02-09 10:56 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-22 19:11 [RFC PATCH net] net/core: don't increment rx_dropped on inactive slaves Jarod Wilson
2016-01-22 20:59 ` Jay Vosburgh
2016-01-23 8:26 ` Jiri Pirko
2016-01-23 8:07 ` Jiri Pirko
2016-01-23 14:19 ` Andy Gospodarek
2016-01-23 15:23 ` Eric Dumazet
2016-01-26 21:14 ` Jarod Wilson
2016-01-26 21:21 ` David Miller
2016-01-26 21:36 ` Jarod Wilson
2016-01-26 21:24 ` Eric Dumazet
2016-01-26 21:35 ` Jarod Wilson
2016-01-25 6:42 ` David Miller
2016-01-25 14:27 ` Jarod Wilson
2016-01-26 4:45 ` Jarod Wilson
2016-01-27 20:21 ` [PATCH net 0/4] net: add rx_unhandled stat counter Jarod Wilson
2016-01-27 20:21 ` [PATCH net 1/4] " Jarod Wilson
2016-01-27 20:21 ` [PATCH net 2/4] net-procfs: show rx_unhandled counters Jarod Wilson
2016-01-27 20:21 ` [PATCH net 3/4] team: track sum of rx_unhandled for all slaves Jarod Wilson
2016-01-27 20:21 ` [PATCH net 4/4] bond: " Jarod Wilson
2016-01-27 21:09 ` [PATCH net 0/4] net: add rx_unhandled stat counter Eric Dumazet
2016-01-28 6:02 ` Jarod Wilson
2016-01-28 6:10 ` Jarod Wilson
2016-01-28 6:18 ` Jarod Wilson
2016-01-28 13:00 ` Eric Dumazet
2016-01-28 14:38 ` Jarod Wilson
2016-01-28 14:42 ` Eric Dumazet
2016-01-28 14:44 ` Eric Dumazet
2016-01-28 14:46 ` Eric Dumazet
2016-01-28 15:11 ` Jarod Wilson
2016-01-28 13:00 ` Eric Dumazet
2016-01-28 15:49 ` [PATCH net v2 0/4] net: add and use rx_nohandler " Jarod Wilson
2016-01-28 15:49 ` [PATCH net v2 2/4] net: add " Jarod Wilson
2016-01-28 15:49 ` [PATCH net v2 3/4] team: track sum of rx_nohandler for all slaves Jarod Wilson
2016-01-28 15:49 ` [PATCH net v2 4/4] bond: " Jarod Wilson
2016-01-30 3:37 ` [PATCH net v2 0/4] net: add and use rx_nohandler stat counter David Miller
2016-01-30 18:16 ` Jarod Wilson
2016-01-30 18:19 ` [PATCH net v2 1/4] net/core: relax BUILD_BUG_ON in netdev_stats_to_stats64 Jarod Wilson
2016-01-30 18:34 ` Eric Dumazet
2016-01-30 20:39 ` Jarod Wilson
2016-01-30 20:53 ` Jarod Wilson
2016-01-30 23:26 ` David Miller
2016-01-31 18:07 ` Jarod Wilson
2016-02-01 23:51 ` [PATCH net v3 0/4] net: add and use rx_nohandler stat counter Jarod Wilson
2016-02-01 23:51 ` [PATCH net v3 1/4] net/core: relax BUILD_BUG_ON in netdev_stats_to_stats64 Jarod Wilson
2016-02-01 23:51 ` [PATCH net v3 2/4] net: add rx_nohandler stat counter Jarod Wilson
2016-02-07 19:37 ` Stephen Hemminger
2016-02-07 19:46 ` David Miller
2016-02-07 20:19 ` Eric Dumazet
2016-02-08 18:32 ` Jarod Wilson
2016-02-08 19:38 ` Stephen Hemminger
2016-02-08 22:57 ` Eric Dumazet
2016-02-09 8:40 ` David Miller
2016-02-09 10:56 ` Jamal Hadi Salim [this message]
2016-02-09 19:17 ` [PATCH net-next iproute2] iplink: display rx nohandler stats Stephen Hemminger
2016-02-09 23:51 ` Jarod Wilson
2016-02-10 1:41 ` Stephen Hemminger
2016-02-10 4:52 ` Eric Dumazet
2016-02-10 13:20 ` Jarod Wilson
2016-02-10 15:06 ` Andy Gospodarek
2016-02-01 23:51 ` [PATCH net v3 3/4] team: track sum of rx_nohandler for all slaves Jarod Wilson
2016-02-01 23:51 ` [PATCH net v3 4/4] bond: " Jarod Wilson
2016-02-06 8:00 ` [PATCH net v3 0/4] net: add and use rx_nohandler stat counter David Miller
2016-01-28 16:22 ` [PATCH net v3 1/4] net/core: relax BUILD_BUG_ON in netdev_stats_to_stats64 Jarod Wilson
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