[PATCH v3 2/3] samples/landlock: Refactor help message

[Matthieu Buffet <matthieu@buffet.re>]

Help message is getting larger with each new supported feature (scopes,
and soon UDP). Also the large number of calls to fprintf with environment
variables make it hard to read. Refactor it away into a single simpler
constant format string.

Signed-off-by: Matthieu Buffet <matthieu@buffet.re>
---
 samples/landlock/sandboxer.c | 79 +++++++++++++++++-------------------
 1 file changed, 38 insertions(+), 41 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index 4cbef9d2f15b..38fc6ebd7222 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -290,6 +290,43 @@ static bool check_ruleset_scope(const char *const env_var,
 
 #define LANDLOCK_ABI_LAST 6
 
+#define XSTR(s) #s
+#define STR(s) XSTR(s)
+
+/* clang-format off */
+
+static const char help[] =
+	"usage: "
+	ENV_FS_RO_NAME "=\"...\" "
+	ENV_FS_RW_NAME "=\"...\" "
+	ENV_TCP_BIND_NAME "=\"...\" "
+	ENV_TCP_CONNECT_NAME "=\"...\" "
+	ENV_SCOPED_NAME "=\"...\" %1$s <cmd> [args]...\n"
+	"\n"
+	"Execute a command in a restricted environment.\n"
+	"\n"
+	"Environment variables containing paths and ports each separated by a colon:\n"
+	"* " ENV_FS_RO_NAME ": list of paths allowed to be used in a read-only way\n"
+	"* " ENV_FS_RW_NAME ": list of paths allowed to be used in a read-write way\n"
+	"\n"
+	"Environment variables containing ports are optional and could be skipped.\n"
+	"* " ENV_TCP_BIND_NAME ": list of ports allowed to bind (server)\n"
+	"* " ENV_TCP_CONNECT_NAME ": list of ports allowed to connect (client)\n"
+	"* " ENV_SCOPED_NAME ": list of scoped IPCs\n"
+	"\n"
+	"Example:\n"
+	ENV_FS_RO_NAME "=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" "
+	ENV_FS_RW_NAME "=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
+	ENV_TCP_BIND_NAME "=\"9418\" "
+	ENV_TCP_CONNECT_NAME "=\"80:443\" "
+	ENV_SCOPED_NAME "=\"a:s\" "
+	"%1$s bash -i\n"
+	"\n"
+	"This sandboxer can use Landlock features up to ABI version "
+	STR(LANDLOCK_ABI_LAST) ".\n";
+
+/* clang-format on */
+
 int main(const int argc, char *const argv[], char *const *const envp)
 {
 	const char *cmd_path;
@@ -308,47 +345,7 @@ int main(const int argc, char *const argv[], char *const *const envp)
 	};
 
 	if (argc < 2) {
-		fprintf(stderr,
-			"usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\" %s "
-			"<cmd> [args]...\n\n",
-			ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
-			ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]);
-		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");
-		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",
-			ENV_FS_RW_NAME);
-		fprintf(stderr,
-			"Environment variables containing ports are optional "
-			"and could be skipped.\n");
-		fprintf(stderr,
-			"* %s: list of ports allowed to bind (server).\n",
-			ENV_TCP_BIND_NAME);
-		fprintf(stderr,
-			"* %s: list of ports allowed to connect (client).\n",
-			ENV_TCP_CONNECT_NAME);
-		fprintf(stderr, "* %s: list of scoped IPCs.\n",
-			ENV_SCOPED_NAME);
-		fprintf(stderr,
-			"\nexample:\n"
-			"%s=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" "
-			"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
-			"%s=\"9418\" "
-			"%s=\"80:443\" "
-			"%s=\"a:s\" "
-			"%s bash -i\n\n",
-			ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
-			ENV_TCP_CONNECT_NAME, ENV_SCOPED_NAME, argv[0]);
-		fprintf(stderr,
-			"This sandboxer can use Landlock features "
-			"up to ABI version %d.\n",
-			LANDLOCK_ABI_LAST);
+		fprintf(stderr, help, argv[0]);
 		return 1;
 	}
 
-- 
2.39.5