Kernel: Make the Jails' internal design a lot more sane

This is done with 2 major steps:
1. Remove JailManagement singleton and use a structure that resembles
    what we have with the Process object. This is required later for the
    second step in this commit, but on its own, is a major change that
    removes this clunky singleton that had no real usage by itself.
2. Use IntrusiveLists to keep references to Process objects in the same
    Jail so it will be much more straightforward to iterate on this kind
    of objects when needed. Previously we locked the entire Process list
    and we did a simple pointer comparison to check if the checked
    Process we iterate on is in the same Jail or not, which required
    taking multiple Spinlocks in a very clumsy and heavyweight way.

Kernel/Jail.cpp

@@ -1,21 +1,70 @@
 /*
- * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ * Copyright (c) 2022-2023, Liav A. <liavalb@hotmail.co.il>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/IntrusiveList.h>
+#include <AK/Singleton.h>
 #include <Kernel/Jail.h>
+#include <Kernel/Process.h>
 
 namespace Kernel {
 
-ErrorOr<NonnullLockRefPtr<Jail>> Jail::create(Badge<JailManagement>, NonnullOwnPtr<KString> name, JailIndex index)
+static Atomic<u64> s_jail_id;
+static Singleton<SpinlockProtected<Jail::List, LockRank::None>> s_all_instances {};
+
+static JailIndex generate_jail_id()
 {
-    return adopt_nonnull_lock_ref_or_enomem(new (nothrow) Jail(move(name), index));
+    return s_jail_id.fetch_add(1);
 }
 
-Jail::Jail(NonnullOwnPtr<KString> name, JailIndex index)
+NonnullRefPtr<ProcessList> Jail::process_list()
+{
+    return m_process_list;
+}
+
+ErrorOr<NonnullLockRefPtr<Jail>> Jail::create(NonnullOwnPtr<KString> name)
+{
+    return s_all_instances->with([&](auto& list) -> ErrorOr<NonnullLockRefPtr<Jail>> {
+        auto process_list = TRY(ProcessList::create());
+        auto jail = TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) Jail(move(name), generate_jail_id(), move(process_list))));
+        list.append(jail);
+        return jail;
+    });
+}
+
+ErrorOr<void> Jail::for_each_when_process_is_not_jailed(Function<ErrorOr<void>(Jail const&)> callback)
+{
+    return Process::current().jail().with([&](auto const& my_jail) -> ErrorOr<void> {
+        // Note: If we are in a jail, don't reveal anything about the outside world,
+        // not even the fact that we are in which jail...
+        if (my_jail)
+            return {};
+        return s_all_instances->with([&](auto& list) -> ErrorOr<void> {
+            for (auto& jail : list) {
+                TRY(callback(jail));
+            }
+            return {};
+        });
+    });
+}
+
+LockRefPtr<Jail> Jail::find_by_index(JailIndex index)
+{
+    return s_all_instances->with([&](auto& list) -> LockRefPtr<Jail> {
+        for (auto& jail : list) {
+            if (jail.index() == index)
+                return jail;
+        }
+        return {};
+    });
+}
+
+Jail::Jail(NonnullOwnPtr<KString> name, JailIndex index, NonnullRefPtr<ProcessList> process_list)
     : m_name(move(name))
     , m_index(index)
+    , m_process_list(move(process_list))
 {
 }
 
@@ -26,7 +75,7 @@ void Jail::detach(Badge<Process>)
         VERIFY(my_attach_count > 0);
         my_attach_count--;
         if (my_attach_count == 0) {
-            m_jail_list_node.remove();
+            m_list_node.remove();
         }
     });
 }