[PATCH v2 3/3] samples/landlock: Clarify option parsing behaviour

[Matthieu Buffet <matthieu@buffet.re>]

- Clarify which environment variables are optional, which ones are
  mandatory
- Clarify the difference between unset variables and empty ones

Signed-off-by: Matthieu Buffet <matthieu@buffet.re>
---
 samples/landlock/sandboxer.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index f16994d35d9e..a28e4a9c5f87 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -298,24 +298,27 @@ static bool check_ruleset_scope(const char *const env_var,
 static void print_help(const char *argv0)
 {
 	fprintf(stderr,
-		"usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s "
+		"usage: %s=\"...\" %s=\"...\" [other environment variables] %s "
 		"<cmd> [args]...\n\n",
-		ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
-		ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv0);
+		ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv0);
 	fprintf(stderr,
 		"Execute a command in a restricted environment.\n\n");
 	fprintf(stderr,
-		"Environment variables containing paths and ports "
-		"each separated by a colon:\n");
+		"All environment variables can be multi-valued, with a "
+		"colon delimiter.\n"
+		"\n"
+		"Mandatory settings:\n");
 	fprintf(stderr,
 		"* %s: list of paths allowed to be used in a read-only way.\n",
 		ENV_FS_RO_NAME);
 	fprintf(stderr,
-		"* %s: list of paths allowed to be used in a read-write way.\n\n",
+		"* %s: list of paths allowed to be used in a read-write way.\n",
 		ENV_FS_RW_NAME);
 	fprintf(stderr,
-		"Environment variables containing ports are optional "
-		"and could be skipped.\n");
+		"\n"
+		"Optional settings (when not set, their associated access "
+		"check is always allowed, which is different from an empty "
+		"string which means an empty list)\n");
 	fprintf(stderr,
 		"* %s: list of ports allowed to bind (server).\n",
 		ENV_TCP_BIND_NAME);
@@ -325,7 +328,8 @@ static void print_help(const char *argv0)
 	fprintf(stderr, "* %s: list of scoped IPCs.\n",
 		ENV_SCOPED_NAME);
 	fprintf(stderr,
-		"\nexample:\n"
+		"\n"
+		"Example:\n"
 		"%s=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" "
 		"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
 		"%s=\"9418\" "
-- 
2.39.2