kata-ctl: Add option to dump config files

Add a `--show-default-config-paths` command line option for parity with
`kata-runtime`.

Note that this requires the `KataCtlCli.command` to be optional so that
the user can run simply:

```bash
$ kata-ctl --show-default-config-paths
```

... without also specifying a (sub-)command.

Fixes: #8640.

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

src/tools/kata-ctl/src/args.rs

@@ -10,10 +10,15 @@ use clap::{Args, Parser, Subcommand, ValueEnum};
 use thiserror::Error;
 
 #[derive(Parser, Debug)]
-#[clap(name = "kata-ctl", author, about = "Kata Containers control tool")]
+#[clap(
+    name = "kata-ctl",
+    author,
+    about = "Kata Containers control tool",
+    arg_required_else_help = true
+)]
 pub struct KataCtlCli {
     #[clap(subcommand)]
-    pub command: Commands,
+    pub command: Option<Commands>,
     #[clap(short, long, value_enum, value_parser = parse_log_level)]
     /// Sets the minimum log level required for log messages to be displayed. Default is 'info'.
     /// Valid values are: trace, debug, info, warning, error, critical
@@ -21,6 +26,10 @@ pub struct KataCtlCli {
     #[clap(short, long, action)]
     /// If enabled, log messages will be JSON formatted for easier machine parsing
     pub json_logging: bool,
+
+    /// If specified, display a list of config file locations.
+    #[clap(long, action)]
+    pub show_default_config_paths: bool,
 }
 
 fn parse_log_level(arg: &str) -> Result<slog::Level, String> {

src/tools/kata-ctl/src/main.rs

@@ -20,12 +20,12 @@ mod utils;
 
 use crate::log_parser::log_parser;
 use anyhow::Result;
-use clap::{crate_name, Parser};
+use args::{Commands, KataCtlCli};
+use clap::{crate_name, CommandFactory, Parser};
+use kata_types::config::TomlConfig;
 use std::io;
 use std::process::exit;
 
-use args::{Commands, KataCtlCli};
-
 use ops::check_ops::{
     handle_check, handle_factory, handle_iptables, handle_metrics, handle_monitor, handle_version,
 };
@@ -43,6 +43,14 @@ macro_rules! sl {
 fn real_main() -> Result<()> {
     let args = KataCtlCli::parse();
 
+    if args.show_default_config_paths {
+        TomlConfig::get_default_config_file_list()
+            .iter()
+            .for_each(|p| println!("{}", p.display()));
+
+        return Ok(());
+    }
+
     let log_level = args.log_level.unwrap_or(slog::Level::Info);
 
     let (logger, _guard) = if args.json_logging {
@@ -53,17 +61,35 @@ fn real_main() -> Result<()> {
 
     let _guard = slog_scope::set_global_logger(logger);
 
-    let res = match args.command {
-        Commands::Check(args) => handle_check(args),
-        Commands::DirectVolume(args) => handle_direct_volume(args),
-        Commands::Exec(args) => handle_exec(args),
-        Commands::Env(args) => handle_env(args),
-        Commands::Factory => handle_factory(),
-        Commands::Iptables(args) => handle_iptables(args),
-        Commands::Metrics(args) => handle_metrics(args),
-        Commands::Monitor(args) => handle_monitor(args),
-        Commands::Version => handle_version(),
-        Commands::LogParser(args) => log_parser(args),
+    let res = if let Some(command) = args.command {
+        match command {
+            Commands::Check(args) => handle_check(args),
+            Commands::DirectVolume(args) => handle_direct_volume(args),
+            Commands::Exec(args) => handle_exec(args),
+            Commands::Env(args) => handle_env(args),
+            Commands::Factory => handle_factory(),
+            Commands::Iptables(args) => handle_iptables(args),
+            Commands::Metrics(args) => handle_metrics(args),
+            Commands::Monitor(args) => handle_monitor(args),
+            Commands::Version => handle_version(),
+            Commands::LogParser(args) => log_parser(args),
+        }
+    } else {
+        // The user specified an option, but not a subcommand. We've already
+        // handled show_default_config_paths, so this is an invalid CLI hence
+        // display usage and exit.
+
+        let help = KataCtlCli::command().render_help().to_string();
+
+        eprintln!("ERROR: need command");
+
+        eprintln!("{help}");
+
+        // We need to exit here rather than returning an error to match clap's
+        // standard behaviour.
+        //
+        // Note: the return value matches the clap-internal USAGE_CODE.
+        exit(2);
     };
 
     // Log errors here, then let the logger go out of scope in main() to ensure