Re: FAILED: patch "[PATCH] test_firmware: fix setting old custom fw path back on exit," failed to apply to 4.16-stable tree

[Ben Hutchings <ben.hutchings@codethink.co.uk>]

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On Sun, 2018-04-29 at 14:36 +0200, gregkh@linuxfoundation.org wrote:
> The patch below does not apply to the 4.16-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
[...]

The attached version should work for 4.4, 4.9, 4.14 and 4.16.

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.

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From f2bdf7cff21eca4755617bfe01146d0741a8fecf Mon Sep 17 00:00:00 2001
From: Ben Hutchings <ben.hutchings@codethink.co.uk>
Date: Tue, 3 Apr 2018 20:39:56 +0100
Subject: [PATCH] test_firmware: fix setting old custom fw path back on exit,
 second try

commit 1dc54bb7046d90447fc92e982f90df57eb3bce37 upstream.

Commit 65c79230576 tried to clear the custom firmware path on exit by
writing a single space to the firmware_class.path parameter.  This
doesn't work because nothing strips this space from the value stored
and fw_get_filesystem_firmware() only ignores zero-length paths.

Instead, write a null byte.

Fixes: 0a8adf58475 ("test: add firmware_class loader test")
Fixes: 65c79230576 ("test_firmware: fix setting old custom fw path back on exit")
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
---
 tools/testing/selftests/firmware/fw_filesystem.sh | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/firmware/fw_filesystem.sh b/tools/testing/selftests/firmware/fw_filesystem.sh
index f9508e1a4058..6b63b6bf2661 100755
--- a/tools/testing/selftests/firmware/fw_filesystem.sh
+++ b/tools/testing/selftests/firmware/fw_filesystem.sh
@@ -46,9 +46,11 @@ test_finish()
 		echo "$OLD_TIMEOUT" >/sys/class/firmware/timeout
 	fi
 	if [ "$OLD_FWPATH" = "" ]; then
-		OLD_FWPATH=" "
+		# A zero-length write won't work; write a null byte
+		printf '\000' >/sys/module/firmware_class/parameters/path
+	else
+		echo -n "$OLD_FWPATH" >/sys/module/firmware_class/parameters/path
 	fi
-	echo -n "$OLD_FWPATH" >/sys/module/firmware_class/parameters/path
 	rm -f "$FW"
 	rmdir "$FWPATH"
 }
-- 
2.11.0