[PATCH v3 1/2] selftests: watchdog: Validate optional file argument

[Eugeniu Rosca <erosca@de.adit-jv.com>]

From: "George G. Davis" <george_davis@mentor.com>

The newly added optional file argument does not validate if the
file is indeed a watchdog, e.g.:

./watchdog-test  -f /dev/zero
Watchdog Ticking Away!

Fix it by confirming that the WDIOC_GETSUPPORT ioctl succeeds.

Fixes: c3f2490d6e9257 ("selftests: watchdog: Add optional file argument")
Reported-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Signed-off-by: George G. Davis <george_davis@mentor.com>
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
---
v3:
 - Used v1 as starting point and simplified commit description
 - Added Fixes tag (WARNING: commit id is from linux-next!)
 - No change in the contents
 - Applied cleanly to the same base as used in [v1]
v2:
 - https://patchwork.kernel.org/patch/11147663/
v1:
 - https://patchwork.kernel.org/patch/11136283/
 - Applied/tested on commit ce54eab71e210f ("kunit: fix failure to build without printk") of
   https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git/log/?h=next
---
 tools/testing/selftests/watchdog/watchdog-test.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tools/testing/selftests/watchdog/watchdog-test.c b/tools/testing/selftests/watchdog/watchdog-test.c
index afff120c7be6..6ed822dc2222 100644
--- a/tools/testing/selftests/watchdog/watchdog-test.c
+++ b/tools/testing/selftests/watchdog/watchdog-test.c
@@ -97,6 +97,7 @@ int main(int argc, char *argv[])
 	int c;
 	int oneshot = 0;
 	char *file = "/dev/watchdog";
+	struct watchdog_info info;
 
 	setbuf(stdout, NULL);
 
@@ -118,6 +119,16 @@ int main(int argc, char *argv[])
 		exit(-1);
 	}
 
+	/*
+	 * Validate that `file` is a watchdog device
+	 */
+	ret = ioctl(fd, WDIOC_GETSUPPORT, &info);
+	if (ret) {
+		printf("WDIOC_GETSUPPORT error '%s'\n", strerror(errno));
+		close(fd);
+		exit(ret);
+	}
+
 	optind = 0;
 
 	while ((c = getopt_long(argc, argv, sopts, lopts, NULL)) != -1) {
-- 
2.23.0