samples/landlock: Refactor help message

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>
Link: https://lore.kernel.org/r/20241019151534.1400605-3-matthieu@buffet.re


[mic: Move the small cleanups in the next commit]
Signed-off-by: Mickaël Salaün <mic@digikod.net>

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;
 	}