Add --list-volumes to list named volumes

Long-only (no free short letter left), lists each volume's name and
host directory, tab-aligned the same way -l/--list-images already
aligns name:tag output -- list_volumes_command() reuses that scheme.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Gv3s5jckJKzh6JkMoi2Akz

src/main.cpp

@@ -41,16 +41,18 @@ namespace {
 
 constexpr std::array<std::string_view, 2> kRequiredTools = {"containers-storage", "bwrap"};
 
-enum class Mode { kNone, kMount, kUnmount, kTest, kRun, kCleanup, kListImages, kVolume };
+enum class Mode { kNone, kMount, kUnmount, kTest, kRun, kCleanup, kListImages, kVolume, kListVolumes };
 
-// --log-level/--user/--group have no short form (--log-level's was freed up so -l
-// could become --list-images; -u is already --umount), so they need long-option
-// vals outside the printable-char range short options use.
+// --log-level/--user/--group/--list-volumes have no short form (--log-level's was
+// freed up so -l could become --list-images; -u is already --umount; --list-volumes
+// has no natural free letter left), so they need long-option vals outside the
+// printable-char range short options use.
 constexpr int kLogLevelOpt = 256;
 constexpr int kUserOpt = 257;
 constexpr int kGroupOpt = 258;
+constexpr int kListVolumesOpt = 259;
 
-constexpr std::array<struct option, 14> kLongOptions = {{
+constexpr std::array<struct option, 15> kLongOptions = {{
     {"help", no_argument, nullptr, 'h'},
     {"version", no_argument, nullptr, 'V'},
     {"test", no_argument, nullptr, 't'},
@@ -64,6 +66,7 @@ constexpr std::array<struct option, 14> kLongOptions = {{
     {"user", required_argument, nullptr, kUserOpt},
     {"group", required_argument, nullptr, kGroupOpt},
     {"volume", required_argument, nullptr, 'v'},
+    {"list-volumes", no_argument, nullptr, kListVolumesOpt},
     {nullptr, 0, nullptr, 0},
 }};
 
@@ -75,6 +78,7 @@ void print_usage(const char* prog) {
         "       {0} -c|--cleanup <layer-id>\n"
         "       {0} -l|--list-images <directory>\n"
         "       {0} -v|--volume <name> <directory>\n"
+        "       {0} --list-volumes\n"
         "       {0} -t|--test\n"
         "       {0} -h|--help\n"
         "       {0} -V|--version\n"
@@ -109,6 +113,8 @@ void print_usage(const char* prog) {
         "  -v, --volume <name> <dir> create a named volume mapped to a host directory\n"
         "                            (created if missing), recorded in the config\n"
         "                            file's volumes section\n"
+        "      --list-volumes        list all named volumes (see -v/--volume) with\n"
+        "                            their host directory\n"
         "  -t, --test                run the test suite\n"
         "      --log-level <level>   set log verbosity (trace, debug, info, warn,\n"
         "                            error, critical, off)\n"
@@ -300,6 +306,25 @@ int create_volume_command(const std::string& name, const std::string& directory,
     return 0;
 }
 
+int list_volumes_command(const AppConfig& config) {
+    size_t max_len = 0;
+    for (const auto& volume : config.volumes) {
+        max_len = std::max(max_len, volume.name.size());
+    }
+
+    // Same tab-alignment scheme as list_images_command(): pad each name to one
+    // 8-column tab stop past the longest one, however long that is.
+    constexpr size_t kTabWidth = 8;
+    size_t target_tabs = max_len / kTabWidth + 1;
+
+    for (const auto& volume : config.volumes) {
+        size_t tabs_used = volume.name.size() / kTabWidth;
+        size_t tabs_needed = target_tabs > tabs_used ? target_tabs - tabs_used : 1;
+        fmt::print("{}{}{}\n", volume.name, std::string(tabs_needed, '\t'), volume.directory);
+    }
+    return 0;
+}
+
 int run_container(const std::filesystem::path& image_tar,
                    const std::vector<std::string>& requested_command, bool use_nsenter,
                    const std::optional<std::string>& user, const std::optional<std::string>& group) {
@@ -387,7 +412,8 @@ int main(int argc, char* argv[]) {
             case 'r':
             case 'c':
             case 'l':
-            case 'v': {
+            case 'v':
+            case kListVolumesOpt: {
                 Mode requested;
                 switch (opt) {
                     case 't':
@@ -408,9 +434,12 @@ int main(int argc, char* argv[]) {
                     case 'l':
                         requested = Mode::kListImages;
                         break;
-                    default:
+                    case 'v':
                         requested = Mode::kVolume;
                         break;
+                    default:
+                        requested = Mode::kListVolumes;
+                        break;
                 }
                 if (mode != Mode::kNone && mode != requested) {
                     spdlog::error("multiple actions specified");
@@ -484,6 +513,9 @@ int main(int argc, char* argv[]) {
     if (mode == Mode::kVolume) {
         return create_volume_command(mode_arg, argv[optind], config_path, *config);
     }
+    if (mode == Mode::kListVolumes) {
+        return list_volumes_command(*config);
+    }
     if (mode == Mode::kRun) {
         std::vector<std::string> command(argv + optind, argv + argc);
         // As root, containers-storage mount doesn't need to reexec into a private