Kernel: Convert SlavePTY all-instances HashTable to an IntrusiveList

This simplifies the DevPtsFS implementation somewhat, as it no longer
requires SlavePTY to register itself with it, since it can now simply
use the list of SlavePTY instances.

Kernel/FileSystem/DevPtsFS.cpp

@@ -1,11 +1,10 @@
 /*
  * Copyright (c) 2019-2020, Sergey Bugaev <bugaevc@serenityos.org>
+ * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/Singleton.h>
-#include <AK/StringView.h>
 #include <Kernel/FileSystem/DevPtsFS.h>
 #include <Kernel/FileSystem/VirtualFileSystem.h>
 #include <Kernel/TTY/SlavePTY.h>
@@ -25,8 +24,6 @@ DevPtsFS::~DevPtsFS()
 {
 }
 
-static Singleton<HashTable<unsigned>> s_ptys;
-
 KResult DevPtsFS::initialize()
 {
     m_root_inode = adopt_ref_if_nonnull(new (nothrow) DevPtsFSInode(*this, 1, nullptr));
@@ -80,16 +77,6 @@ RefPtr<Inode> DevPtsFS::get_inode(InodeIdentifier inode_id) const
     return inode;
 }
 
-void DevPtsFS::register_slave_pty(SlavePTY& slave_pty)
-{
-    s_ptys->set(slave_pty.index());
-}
-
-void DevPtsFS::unregister_slave_pty(SlavePTY& slave_pty)
-{
-    s_ptys->remove(slave_pty.index());
-}
-
 DevPtsFSInode::DevPtsFSInode(DevPtsFS& fs, InodeIndex index, SlavePTY* pty)
     : Inode(fs, index)
 {
@@ -129,11 +116,13 @@ KResult DevPtsFSInode::traverse_as_directory(Function<bool(FileSystem::Directory
     callback({ ".", identifier(), 0 });
     callback({ "..", identifier(), 0 });
 
-    for (unsigned pty_index : *s_ptys) {
-        String name = String::number(pty_index);
-        InodeIdentifier identifier = { fsid(), pty_index_to_inode_index(pty_index) };
-        callback({ name, identifier, 0 });
-    }
+    SlavePTY::all_instances().with([&](auto& list) {
+        for (SlavePTY& slave_pty : list) {
+            String name = String::number(slave_pty.index());
+            InodeIdentifier identifier = { fsid(), pty_index_to_inode_index(slave_pty.index()) };
+            callback({ name, identifier, 0 });
+        }
+    });
 
     return KSuccess;
 }
@@ -146,14 +135,20 @@ KResultOr<NonnullRefPtr<Inode>> DevPtsFSInode::lookup(StringView name)
         return *this;
 
     auto pty_index = name.to_uint();
-    if (pty_index.has_value() && s_ptys->contains(pty_index.value())) {
-        auto inode = fs().get_inode({ fsid(), pty_index_to_inode_index(pty_index.value()) });
-        if (!inode)
-            return ENOENT;
-        return inode.release_nonnull();
-    }
+    if (!pty_index.has_value())
+        return ENOENT;
 
-    return ENOENT;
+    return SlavePTY::all_instances().with([&](auto& list) -> KResultOr<NonnullRefPtr<Inode>> {
+        for (SlavePTY& slave_pty : list) {
+            if (slave_pty.index() != pty_index.value())
+                continue;
+            auto inode = fs().get_inode({ fsid(), pty_index_to_inode_index(pty_index.value()) });
+            if (!inode)
+                return ENOENT;
+            return inode.release_nonnull();
+        }
+        return ENOENT;
+    });
 }
 
 void DevPtsFSInode::flush_metadata()

Kernel/FileSystem/DevPtsFS.h

@@ -27,9 +27,6 @@ public:
 
     virtual Inode& root_inode() override;
 
-    static void register_slave_pty(SlavePTY&);
-    static void unregister_slave_pty(SlavePTY&);
-
 private:
     DevPtsFS();
     RefPtr<Inode> get_inode(InodeIdentifier) const;

Kernel/TTY/SlavePTY.cpp

@@ -1,9 +1,10 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/Singleton.h>
 #include <Kernel/Debug.h>
 #include <Kernel/FileSystem/DevPtsFS.h>
 #include <Kernel/Process.h>
@@ -12,6 +13,26 @@
 
 namespace Kernel {
 
+static Singleton<SpinLockProtectedValue<SlavePTY::List>> s_all_instances;
+
+SpinLockProtectedValue<SlavePTY::List>& SlavePTY::all_instances()
+{
+    return s_all_instances;
+}
+
+bool SlavePTY::unref() const
+{
+    bool did_hit_zero = SlavePTY::all_instances().with([&](auto&) {
+        if (deref_base())
+            return false;
+        m_list_node.remove();
+        return true;
+    });
+    if (did_hit_zero)
+        delete this;
+    return did_hit_zero;
+}
+
 SlavePTY::SlavePTY(MasterPTY& master, unsigned index)
     : TTY(201, index)
     , m_master(master)
@@ -21,14 +42,14 @@ SlavePTY::SlavePTY(MasterPTY& master, unsigned index)
     auto process = Process::current();
     set_uid(process->uid());
     set_gid(process->gid());
-    DevPtsFS::register_slave_pty(*this);
     set_size(80, 25);
+
+    SlavePTY::all_instances().with([&](auto& list) { list.append(*this); });
 }
 
 SlavePTY::~SlavePTY()
 {
     dbgln_if(SLAVEPTY_DEBUG, "~SlavePTY({})", m_index);
-    DevPtsFS::unregister_slave_pty(*this);
 }
 
 String const& SlavePTY::tty_name() const

Kernel/TTY/SlavePTY.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -15,6 +15,7 @@ class MasterPTY;
 
 class SlavePTY final : public TTY {
 public:
+    virtual bool unref() const override;
     virtual ~SlavePTY() override;
 
     void on_master_write(const UserOrKernelBuffer&, size_t);
@@ -47,6 +48,12 @@ private:
     time_t m_time_of_last_write { 0 };
     unsigned m_index { 0 };
     String m_tty_name;
+
+    mutable IntrusiveListNode<SlavePTY> m_list_node;
+
+public:
+    using List = IntrusiveList<SlavePTY, RawPtr<SlavePTY>, &SlavePTY::m_list_node>;
+    static SpinLockProtectedValue<SlavePTY::List>& all_instances();
 };
 
 }