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From:   Matthieu Baerts <matthieu.baerts@tessares.net>
Date:   Sun, 28 May 2023 19:35:26 +0200
Subject: [PATCH net 1/8] selftests: mptcp: join: avoid using 'cmp --bytes'
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Message-Id: <20230528-upstream-net-20230528-mptcp-selftests-support-old-kernels-part-1-v1-1-a32d85577fc6@tessares.net>
References: <20230528-upstream-net-20230528-mptcp-selftests-support-old-kernels-part-1-v1-0-a32d85577fc6@tessares.net>
In-Reply-To: <20230528-upstream-net-20230528-mptcp-selftests-support-old-kernels-part-1-v1-0-a32d85577fc6@tessares.net>
To:     mptcp@lists.linux.dev, Mat Martineau <martineau@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, Shuah Khan <shuah@kernel.org>,
        Christoph Paasch <cpaasch@apple.com>,
        Florian Westphal <fw@strlen.de>,
        Davide Caratti <dcaratti@redhat.com>,
        Kishen Maloor <kishen.maloor@intel.com>
Cc:     netdev@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Matthieu Baerts <matthieu.baerts@tessares.net>,
        stable@vger.kernel.org
Precedence: bulk

BusyBox's 'cmp' command doesn't support the '--bytes' parameter.

Some CIs -- i.e. LKFT -- use BusyBox and have the mptcp_join.sh test
failing [1] because their 'cmp' command doesn't support this '--bytes'
option:

    cmp: unrecognized option '--bytes=1024'
    BusyBox v1.35.0 () multi-call binary.

    Usage: cmp [-ls] [-n NUM] FILE1 [FILE2]

Instead, 'head --bytes' can be used as this option is supported by
BusyBox. A temporary file is needed for this operation.

Because it is apparently quite common to use BusyBox, it is certainly
better to backport this fix to impacted kernels.

Fixes: 6bf41020b72b ("selftests: mptcp: update and extend fastclose test-cases")
Cc: stable@vger.kernel.org
Link: https://qa-reports.linaro.org/lkft/linux-mainline-master/build/v6.3-rc5-5-g148341f0a2f5/testrun/16088933/suite/kselftest-net-mptcp/test/net_mptcp_userspace_pm_sh/log [1]
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
---
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 26310c17b4c6..4f3fe45f8f71 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -17,6 +17,7 @@ sout=""
 cin=""
 cinfail=""
 cinsent=""
+tmpfile=""
 cout=""
 capout=""
 ns1=""
@@ -175,6 +176,7 @@ cleanup()
 {
 	rm -f "$cin" "$cout" "$sinfail"
 	rm -f "$sin" "$sout" "$cinsent" "$cinfail"
+	rm -f "$tmpfile"
 	rm -rf $evts_ns1 $evts_ns2
 	cleanup_partial
 }
@@ -383,9 +385,16 @@ check_transfer()
 			fail_test
 			return 1
 		fi
-		bytes="--bytes=${bytes}"
+
+		# note: BusyBox's "cmp" command doesn't support --bytes
+		tmpfile=$(mktemp)
+		head --bytes="$bytes" "$in" > "$tmpfile"
+		mv "$tmpfile" "$in"
+		head --bytes="$bytes" "$out" > "$tmpfile"
+		mv "$tmpfile" "$out"
+		tmpfile=""
 	fi
-	cmp -l "$in" "$out" ${bytes} | while read -r i a b; do
+	cmp -l "$in" "$out" | while read -r i a b; do
 		local sum=$((0${a} + 0${b}))
 		if [ $check_invert -eq 0 ] || [ $sum -ne $((0xff)) ]; then
 			echo "[ FAIL ] $what does not match (in, out):"

-- 
2.39.2