From: Horatiu Vultur <horatiu.vultur@microchip.com>
To: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: <netdev@vger.kernel.org>, Andrew Lunn <andrew@lunn.ch>,
Jakub Kicinski <kuba@kernel.org>,
"David S . Miller" <davem@davemloft.net>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net v2 1/2] net: mrp: fix definitions of MRP test packets
Date: Thu, 21 Jan 2021 22:23:40 +0100 [thread overview]
Message-ID: <20210121212340.dtvdkm4nnqcqjhss@soft-dev3.localdomain> (raw)
In-Reply-To: <20210121204037.61390-2-rasmus.villemoes@prevas.dk>
The 01/21/2021 21:40, Rasmus Villemoes wrote:
It seems that is missing a Fixes tag, other than that it looks fine.
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
>
> Wireshark says that the MRP test packets cannot be decoded - and the
> reason for that is that there's a two-byte hole filled with garbage
> between the "transitions" and "timestamp" members.
>
> So Wireshark decodes the two garbage bytes and the top two bytes of
> the timestamp written by the kernel as the timestamp value (which thus
> fluctuates wildly), and interprets the lower two bytes of the
> timestamp as a new (type, length) pair, which is of course broken.
>
> Even though this makes the timestamp field in the struct unaligned, it
> actually makes it end up on a 32 bit boundary in the frame as mandated
> by the standard, since it is preceded by a two byte TLV header.
>
> The struct definitions live under include/uapi/, but they are not
> really part of any kernel<->userspace API/ABI, so fixing the
> definitions by adding the packed attribute should not cause any
> compatibility issues.
>
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
> ---
> include/uapi/linux/mrp_bridge.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/mrp_bridge.h b/include/uapi/linux/mrp_bridge.h
> index 6aeb13ef0b1e..d1d0cf65916d 100644
> --- a/include/uapi/linux/mrp_bridge.h
> +++ b/include/uapi/linux/mrp_bridge.h
> @@ -96,7 +96,7 @@ struct br_mrp_ring_test_hdr {
> __be16 state;
> __be16 transitions;
> __be32 timestamp;
> -};
> +} __attribute__((__packed__));
>
> struct br_mrp_ring_topo_hdr {
> __be16 prio;
> @@ -141,7 +141,7 @@ struct br_mrp_in_test_hdr {
> __be16 state;
> __be16 transitions;
> __be32 timestamp;
> -};
> +} __attribute__((__packed__));
>
> struct br_mrp_in_topo_hdr {
> __u8 sa[ETH_ALEN];
> --
> 2.23.0
>
--
/Horatiu
next prev parent reply other threads:[~2021-01-21 21:25 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 20:40 [PATCH net v2 0/2] fix and move definitions of MRP data structures Rasmus Villemoes
2021-01-21 20:40 ` [PATCH net v2 1/2] net: mrp: fix definitions of MRP test packets Rasmus Villemoes
2021-01-21 21:23 ` Horatiu Vultur [this message]
2021-01-21 21:28 ` Rasmus Villemoes
2021-01-21 20:40 ` [PATCH net v2 2/2] net: mrp: move struct definitions out of uapi Rasmus Villemoes
2021-01-23 20:40 ` [PATCH net v2 0/2] fix and move definitions of MRP data structures Jakub Kicinski
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