tree a6f7d3d19c0829b376dd4933373969c43e6da762
parent 98baa5d6aa82022b3703e91aa894e90318c1ef42
author Slawek Kaplonski <skaplons@redhat.com> 1621457313 +0200
committer Slawek Kaplonski <skaplons@redhat.com> 1621457924 +0200

Change way how tcpdump result is checked in multicast test

In the multicast scenario test, when IGMP snooping is enabled thus
multicast traffic shouldn't be delivered to the unregistered node.
To check that this is true, we run tcpdump on the unregistered node
with filter to catch multicast packets and we assert that any packet
wasn't captured by tcpdump.
The problem is that we were expeciting in the actual tcpdump message
string like:

    '0 packets captured\n0 packets received by filter'

and that can cause problem as sometimes test is failing due to output
like:

    '0 packets captured
     3 packets received by filter
     0 packets dropped by kernel'

Now, according to the tcpdump manpage [1] meaning of the "packets
received by filter" is like below:

    "the meaning of this depends on the OS on which you're running
    tcpdump, and possibly on the way the OS was configured - if a
    filter was specified on the command line, on some OSes it counts
    packets regardless of whether they were matched by the filter
    expression and, even if they were matched by the filter expression,
    regardless of whether tcpdump has read and processed them yet,
    on other OSes it counts only packets that were matched by
    the filter expression regardless of whether tcpdump has read and
    processed them yet, and on other OSes it counts only packets that
    were matched by the filter expression and were processed by
    tcpdump"

So to avoid failured to due packets "received by filter", lets just
match on packets "captured" as in case of this test, when we are using
"-c1" switch in tcpdump that should be enough.

[1] https://www.tcpdump.org/manpages/tcpdump.1.html

Closes-Bug: #1926780
Change-Id: If36931beecd53c0767a5de5fd01f861961385049