[PATCH v2 2/3] samples/landlock: Refactor --help message in function

[Mickaël Salaün]

This series looks good to me, but each patch still needs to pass
clang-format.

On Thu, Oct 03, 2024 at 02:50:41AM +0200, Matthieu Buffet wrote:
> Help message is getting larger with each new supported feature (scopes,
> and soon UDP). Refactor it away into a separate helper function.
> 
> Signed-off-by: Matthieu Buffet <matthieu at buffet.re>
> ---
>  samples/landlock/sandboxer.c | 87 +++++++++++++++++++-----------------
>  1 file changed, 46 insertions(+), 41 deletions(-)
> 
> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
> index aff5ef808e22..f16994d35d9e 100644
> --- a/samples/landlock/sandboxer.c
> +++ b/samples/landlock/sandboxer.c
> @@ -295,6 +295,51 @@ static bool check_ruleset_scope(const char *const env_var,
>  
>  #define LANDLOCK_ABI_LAST 6
>  
> +static void print_help(const char *argv0)
> +{
> +	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, 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");
> +	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, argv0);
> +	fprintf(stderr,
> +		"This sandboxer can use Landlock features "
> +		"up to ABI version %d.\n",
> +		LANDLOCK_ABI_LAST);
> +}

While we are at it, could you please transform this set of fprintf()
calls to a static const char[] with "%1$s" where we need argv0, and use
the defined constants in place instead of %s (with string conversion for
the ABI).  This would make the whole help easier to read and maintain.

We'll need some help from the preprocessor as explained in
https://gcc.gnu.org/onlinedocs/cpp/Stringizing.html:

#define XSTR(s) STR(s)
#define STR(s) #s

static const char help[] =
"usage: " ENV_FS_RO_NAME "=\"...\" [...] %1$s "
[...]
"up to ABI version " XSTR(LANDLOCK_ABI_LAST) ".\n";

> +
>  int main(const int argc, char *const argv[], char *const *const envp)
>  {
>  	const char *cmd_path;
> @@ -313,47 +358,7 @@ 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);
> +		print_help(argv[0]);
>  		return 1;
>  	}
>  
> -- 
> 2.39.2
> 
>