lkml.org 
[lkml]   [2020]   [Dec]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH net 1/2] net: mrp: fix definitions of MRP test packets
    On Wed, 23 Dec 2020 15:45:32 +0100 Rasmus Villemoes wrote:
    > 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.
    >
    > While my copy of the MRP standard is still under way [*], I cannot
    > imagine the standard specifying a two-byte hole here, and whoever
    > wrote the Wireshark decoding code seems to agree with that.
    >
    > 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.
    >
    > The remaining on-the-wire packet formats likely also don't contain
    > holes, but pahole and manual inspection says the current definitions
    > suffice. So adding the packed attribute to those is not strictly
    > needed, but might be done for good measure.
    >
    > [*] I will never understand how something hidden behind a +1000$
    > paywall can be called a standard.
    >
    > 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];

    Can we use this opportunity to move the definitions of these structures
    out of the uAPI to a normal kernel header?

    \
     
     \ /
      Last update: 2020-12-28 23:58    [W:3.221 / U:0.052 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site