kublk stores at most MAX_BACK_FILES backing file arguments. The
argument parser currently stops collecting paths when that limit is
reached and silently ignores any remaining paths.

Reject the command instead so that a test cannot accidentally run with
fewer backing files than requested. Add a regression test that exercises
the error without requiring a ublk device.

Fixes: 6aecda00b7d1 ("selftests: ublk: add kernel selftests for ublk")
Assisted-by: LLM
Signed-off-by: Ruben Sutton <ruben@scstudios.tech>
---
 tools/testing/selftests/ublk/Makefile       |  4 +++-
 tools/testing/selftests/ublk/kublk.c        |  5 +++++
 tools/testing/selftests/ublk/test_cli_01.sh | 15 +++++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100755 tools/testing/selftests/ublk/test_cli_01.sh

diff --git a/tools/testing/selftests/ublk/Makefile b/tools/testing/selftests/ublk/Makefile
index 5daf36c6c3..28ce542d4e 100644
--- a/tools/testing/selftests/ublk/Makefile
+++ b/tools/testing/selftests/ublk/Makefile
@@ -7,7 +7,9 @@ endif
 
 LDLIBS += -lpthread -lm -luring
 
-TEST_PROGS := test_generic_02.sh
+TEST_PROGS := test_cli_01.sh
+
+TEST_PROGS += test_generic_02.sh
 TEST_PROGS += test_generic_03.sh
 TEST_PROGS += test_generic_06.sh
 TEST_PROGS += test_generic_07.sh
diff --git a/tools/testing/selftests/ublk/kublk.c b/tools/testing/selftests/ublk/kublk.c
index 2400b46157..3af2f10ca8 100644
--- a/tools/testing/selftests/ublk/kublk.c
+++ b/tools/testing/selftests/ublk/kublk.c
@@ -2525,6 +2525,11 @@ int main(int argc, char *argv[])
 	while (i < argc && ctx.nr_files < MAX_BACK_FILES) {
 		ctx.files[ctx.nr_files++] = argv[i++];
 	}
+	if (i < argc) {
+		fprintf(stderr, "too many backing files (maximum is %d)\n",
+			MAX_BACK_FILES);
+		return -EINVAL;
+	}
 
 	ops = ublk_find_tgt(ctx.tgt_type);
 	if (ops && ops->parse_cmd_line) {
diff --git a/tools/testing/selftests/ublk/test_cli_01.sh b/tools/testing/selftests/ublk/test_cli_01.sh
new file mode 100755
index 0000000000..e937b8e20b
--- /dev/null
+++ b/tools/testing/selftests/ublk/test_cli_01.sh
@@ -0,0 +1,15 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+UBLK_PROG="$(dirname "$0")/kublk"
+expected="too many backing files (maximum is 4)"
+
+if output=$("${UBLK_PROG}" add -t stripe a b c d e 2>&1); then
+	echo "kublk accepted more than four backing files"
+	exit 1
+fi
+
+if [ "${output}" != "${expected}" ]; then
+	echo "unexpected error: ${output}"
+	exit 1
+fi

base-commit: 893e11787f78e43b534e252249ac3fff4d1333f8
-- 
2.54.0 (Apple Git-157)