[PATCH v2 3/3] selftests: ublk: add test to verify that feat_map is complete

[Uday Shankar <ushankar@purestorage.com>]

Add a test that verifies that the currently running kernel does not
report support for any features that are unrecognized by kublk. This
should catch cases where features are added without updating kublk's
feat_map accordingly, which has happened multiple times in the past (see
[1], [2]).

Note that this new test may fail if the test suite is older than the
kernel, and the newer kernel contains a newly introduced feature. I
believe this is not a use case we currently care about - we only care
about newer test suites passing on older kernels.

[1] https://lore.kernel.org/linux-block/20250606214011.2576398-1-csander@purestorage.com/t/#u
[2] https://lore.kernel.org/linux-block/2a370ab1-d85b-409d-b762-f9f3f6bdf705@nvidia.com/t/#m1c520a058448d594fd877f07804e69b28908533f

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
---
 tools/testing/selftests/ublk/Makefile           |  1 +
 tools/testing/selftests/ublk/test_generic_13.sh | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/tools/testing/selftests/ublk/Makefile b/tools/testing/selftests/ublk/Makefile
index 5d7f4ecfb81612f919a89eb442f948d6bfafe225..770269efe42ab460366485ccc80abfa145a0c57b 100644
--- a/tools/testing/selftests/ublk/Makefile
+++ b/tools/testing/selftests/ublk/Makefile
@@ -20,6 +20,7 @@ TEST_PROGS += test_generic_09.sh
 TEST_PROGS += test_generic_10.sh
 TEST_PROGS += test_generic_11.sh
 TEST_PROGS += test_generic_12.sh
+TEST_PROGS += test_generic_13.sh
 
 TEST_PROGS += test_null_01.sh
 TEST_PROGS += test_null_02.sh
diff --git a/tools/testing/selftests/ublk/test_generic_13.sh b/tools/testing/selftests/ublk/test_generic_13.sh
new file mode 100755
index 0000000000000000000000000000000000000000..b7aa90b1cb74615dd4727187a6a5aa9ed93088f7
--- /dev/null
+++ b/tools/testing/selftests/ublk/test_generic_13.sh
@@ -0,0 +1,20 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+. "$(cd "$(dirname "$0")" && pwd)"/test_common.sh
+
+TID="generic_13"
+ERR_CODE=0
+
+_prep_test "null" "check that feature list is complete"
+
+if ${UBLK_PROG} features | grep -q unknown; then
+        echo "# unknown feature detected!"
+        echo "# did you add a feature and forget to update feat_map in kublk?"
+        echo "# this failure is expected if running an older test suite against"
+        echo "# a newer kernel with new features added"
+        ERR_CODE=255
+fi
+
+_cleanup_test "null"
+_show_result $TID $ERR_CODE

-- 
2.34.1