Utilities: Add a new utility to hold a file descriptor open on a path

It helps checking permissions (RW or read-only) of a path and allows us
to keep a file descriptor open on a path, hence keeping the responsible
mount busy.

Author: supercomputer7

Userland/Utilities/CMakeLists.txt

@@ -1,5 +1,6 @@
 set(CMD_SOURCES_CPP
     abench.cpp
+    access.cpp
     aconv.cpp
     adjtime.cpp
     allocate.cpp
@@ -241,7 +242,7 @@ list(APPEND REQUIRED_TARGETS
 )
 list(APPEND RECOMMENDED_TARGETS
     aconv adjtime aplay abench asctl bt checksum chres cksum copy fortune gzip install keymap lsdev lsirq lsof lspci lzcat man mkfs.fat mknod mktemp
-    nc netstat notify ntpquery open passwd pixelflut pls printf pro shot strings tar tt unzip wallpaper xzcat zip
+    nc netstat notify ntpquery open access passwd pixelflut pls printf pro shot strings tar tt unzip wallpaper xzcat zip
 )
 
 # FIXME: Support specifying component dependencies for utilities (e.g. WebSocket for telws)

Userland/Utilities/access.cpp

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2020, Sergey Bugaev <bugaevc@serenityos.org>
+ * Copyright (c) 2020, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/ArgsParser.h>
+#include <LibCore/System.h>
+#include <LibMain/Main.h>
+#include <fcntl.h>
+#include <stdint.h>
+
+ErrorOr<int> serenity_main(Main::Arguments arguments)
+{
+    StringView path;
+    Core::ArgsParser parser;
+    bool readonly = false;
+    bool dont_exit_on_success = false;
+    parser.set_general_help("Open a file in a filesystem in the intention to keep the mount busy.");
+    parser.add_option(readonly, "Open in read-only mode", "readonly", 'r');
+    parser.add_option(dont_exit_on_success, "Don't exit on success", "keep-access", 's');
+    parser.add_positional_argument(path, "file path to open", "path");
+    parser.parse(arguments);
+
+    int fd = -1;
+    if (readonly)
+        fd = TRY(Core::System::open(path, O_RDONLY));
+    else
+        fd = TRY(Core::System::open(path, O_RDWR));
+
+    (void)fd;
+
+    if (!dont_exit_on_success)
+        return 0;
+
+    while (true) {
+    }
+
+    return 0;
+}