Userland: Add the losetup utility to manage loop devices

The new utility implements an option to create a new loop device based
on path of source image, as well as an option to delete an existing
device.

Base/usr/share/man/man1/losetup.md

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+## Name
+
+losetup - manage loop devices
+
+## Synopsis
+
+```**sh
+$ losetup [options...] [path]
+```
+
+## Description
+
+losetup is a utility for managing loop devices. It can create new devices or delete
+existing ones.
+
+## Options
+
+* `-d`, `--delete`: Remove an existing loop device based on the `path` argument.
+* `-c`, `--create`: Create a new loop device based on the `path` argument.
+
+## Files
+
+* `/dev/devctl` - device control device inode, which allows creating and deleting loop devices.
+
+## Examples
+
+```sh
+$ losetup -c test.img
+Created new device at /dev/loop/0
+$ losetup -d /dev/loop/0
+```

Userland/Utilities/losetup.cpp

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+/*
+ * Copyright (c) 2024, Liav A. <[email protected]>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/String.h>
+#include <AK/StringUtils.h>
+#include <AK/StringView.h>
+#include <LibCore/ArgsParser.h>
+#include <LibCore/File.h>
+#include <LibCore/System.h>
+#include <LibMain/Main.h>
+
+ErrorOr<int> serenity_main(Main::Arguments arguments)
+{
+    TRY(Core::System::pledge("stdio rpath wpath"));
+    StringView path;
+    bool flag_delete_device = false;
+    bool flag_add_new_device = false;
+
+    Core::ArgsParser args_parser;
+    args_parser.set_general_help("Manage loop devices.");
+    args_parser.add_option(flag_delete_device, "Delete a loop device", "delete", 'd');
+    args_parser.add_option(flag_add_new_device, "Add new device", "create", 'c');
+    args_parser.add_positional_argument(path, "Path", "path", Core::ArgsParser::Required::No);
+    args_parser.parse(arguments);
+
+    if (!(flag_delete_device || flag_add_new_device))
+        return Error::from_string_literal("No specified option was requested.");
+
+    if (path.is_null())
+        return Error::from_string_literal("No specified path to handle.");
+
+    auto devctl_device = TRY(Core::File::open("/dev/devctl"sv, Core::File::OpenMode::Read));
+    if (flag_delete_device) {
+        constexpr StringView base_dev_loop_path = "/dev/loop/"sv;
+        if (!path.starts_with(base_dev_loop_path))
+            return Error::from_string_literal("Invalid loop device path.");
+        auto number = path.substring_view(base_dev_loop_path.length());
+        auto possible_number = number.to_number<u64>();
+        if (!possible_number.has_value())
+            return Error::from_string_literal("Invalid loop device number.");
+        auto loop_device_index = possible_number.release_value();
+        TRY(Core::System::ioctl(devctl_device->fd(), DEVCTL_DESTROY_LOOP_DEVICE, &loop_device_index));
+        return 0;
+    }
+
+    VERIFY(flag_add_new_device);
+    auto value = TRY(Core::System::open(path, O_RDWR));
+    TRY(Core::System::ioctl(devctl_device->fd(), DEVCTL_CREATE_LOOP_DEVICE, &value));
+    int loop_device_index = value;
+
+    auto loop_device_path = TRY(String::formatted("/dev/loop/{}", loop_device_index));
+    outln("Created new device at {}", loop_device_path);
+    return 0;
+}