Kernel: Move TTY subsystem to use KString instead of AK::String

This is minor progress on removing the `AK::String` API from the Kernel
in the interest of improving OOM safety.

Kernel/GlobalProcessExposed.cpp

@@ -497,7 +497,7 @@ private:
             process_object.add("nfds", process.fds().open_count());
             process_object.add("name", process.name());
             process_object.add("executable", process.executable() ? process.executable()->absolute_path() : "");
-            process_object.add("tty", process.tty() ? process.tty()->tty_name() : "notty");
+            process_object.add("tty", process.tty() ? process.tty()->tty_name().view() : "notty"sv);
             process_object.add("amount_virtual", process.address_space().amount_virtual());
             process_object.add("amount_resident", process.address_space().amount_resident());
             process_object.add("amount_dirty_private", process.address_space().amount_dirty_private());

Kernel/Syscalls/ttyname.cpp

@@ -18,7 +18,7 @@ KResultOr<FlatPtr> Process::sys$ttyname(int fd, Userspace<char*> buffer, size_t
     auto description = TRY(fds().open_file_description(fd));
     if (!description->is_tty())
         return ENOTTY;
-    auto tty_name = description->tty()->tty_name();
+    auto& tty_name = description->tty()->tty_name();
     if (size < tty_name.length() + 1)
         return ERANGE;
     return copy_to_user(buffer, tty_name.characters(), tty_name.length() + 1);
@@ -32,7 +32,7 @@ KResultOr<FlatPtr> Process::sys$ptsname(int fd, Userspace<char*> buffer, size_t
     auto* master_pty = description->master_pty();
     if (!master_pty)
         return ENOTTY;
-    auto pts_name = master_pty->pts_name();
+    auto& pts_name = master_pty->pts_name();
     if (size < pts_name.length() + 1)
         return ERANGE;
     return copy_to_user(buffer, pts_name.characters(), pts_name.length() + 1);

Kernel/TTY/MasterPTY.cpp

@@ -18,21 +18,25 @@ namespace Kernel {
 
 KResultOr<NonnullRefPtr<MasterPTY>> MasterPTY::try_create(unsigned int index)
 {
+    // FIXME: Don't make a temporary String here
+    auto pts_name = TRY(KString::try_create(String::formatted("/dev/pts/{}", index)));
+    auto tty_name = TRY(pts_name->try_clone());
+
     auto buffer = TRY(DoubleBuffer::try_create());
-    auto master_pty = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) MasterPTY(index, move(buffer))));
+    auto master_pty = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) MasterPTY(index, move(buffer), move(pts_name))));
-    auto slave_pty = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) SlavePTY(*master_pty, index)));
+    auto slave_pty = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) SlavePTY(*master_pty, index, move(tty_name))));
     master_pty->m_slave = slave_pty;
     master_pty->after_inserting();
     slave_pty->after_inserting();
     return master_pty;
 }
 
-MasterPTY::MasterPTY(unsigned index, NonnullOwnPtr<DoubleBuffer> buffer)
+MasterPTY::MasterPTY(unsigned index, NonnullOwnPtr<DoubleBuffer> buffer, NonnullOwnPtr<KString> pts_name)
     : CharacterDevice(200, index)
     , m_index(index)
     , m_buffer(move(buffer))
+    , m_pts_name(move(pts_name))
 {
-    m_pts_name = String::formatted("/dev/pts/{}", m_index);
     auto& process = Process::current();
     set_uid(process.uid());
     set_gid(process.gid());
@@ -49,9 +53,9 @@ MasterPTY::~MasterPTY()
     PTYMultiplexer::the().notify_master_destroyed({}, m_index);
 }
 
-String MasterPTY::pts_name() const
+KString const& MasterPTY::pts_name() const
 {
-    return m_pts_name;
+    return *m_pts_name;
 }
 
 KResultOr<size_t> MasterPTY::read(OpenFileDescription&, u64, UserOrKernelBuffer& buffer, size_t size)

Kernel/TTY/MasterPTY.h

@@ -20,7 +20,7 @@ public:
     virtual ~MasterPTY() override;
 
     unsigned index() const { return m_index; }
-    String pts_name() const;
+    KString const& pts_name() const;
     KResultOr<size_t> on_slave_write(const UserOrKernelBuffer&, size_t);
     bool can_write_from_slave() const;
     void notify_slave_closed(Badge<SlavePTY>);
@@ -29,7 +29,7 @@ public:
     virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const override;
 
 private:
-    explicit MasterPTY(unsigned index, NonnullOwnPtr<DoubleBuffer> buffer);
+    explicit MasterPTY(unsigned index, NonnullOwnPtr<DoubleBuffer> buffer, NonnullOwnPtr<KString> pts_name);
     // ^CharacterDevice
     virtual KResultOr<size_t> read(OpenFileDescription&, u64, UserOrKernelBuffer&, size_t) override;
     virtual KResultOr<size_t> write(OpenFileDescription&, u64, const UserOrKernelBuffer&, size_t) override;
@@ -44,7 +44,7 @@ private:
     unsigned m_index;
     bool m_closed { false };
     NonnullOwnPtr<DoubleBuffer> m_buffer;
-    String m_pts_name;
+    NonnullOwnPtr<KString> m_pts_name;
 };
 
 }

Kernel/TTY/SlavePTY.cpp

@@ -35,12 +35,12 @@ bool SlavePTY::unref() const
     return did_hit_zero;
 }
 
-SlavePTY::SlavePTY(MasterPTY& master, unsigned index)
+SlavePTY::SlavePTY(MasterPTY& master, unsigned index, NonnullOwnPtr<KString> tty_name)
     : TTY(201, index)
     , m_master(master)
     , m_index(index)
+    , m_tty_name(move(tty_name))
 {
-    m_tty_name = String::formatted("/dev/pts/{}", m_index);
     auto& process = Process::current();
     set_uid(process.uid());
     set_gid(process.gid());
@@ -54,9 +54,9 @@ SlavePTY::~SlavePTY()
     dbgln_if(SLAVEPTY_DEBUG, "~SlavePTY({})", m_index);
 }
 
-String const& SlavePTY::tty_name() const
+KString const& SlavePTY::tty_name() const
 {
-    return m_tty_name;
+    return *m_tty_name;
 }
 
 void SlavePTY::echo(u8 ch)

Kernel/TTY/SlavePTY.h

@@ -27,7 +27,7 @@ public:
 
 private:
     // ^TTY
-    virtual String const& tty_name() const override;
+    virtual KString const& tty_name() const override;
     virtual KResultOr<size_t> on_tty_write(const UserOrKernelBuffer&, size_t) override;
     virtual void echo(u8) override;
 
@@ -39,12 +39,12 @@ private:
     virtual KResult close() override;
 
     friend class MasterPTY;
-    SlavePTY(MasterPTY&, unsigned index);
+    SlavePTY(MasterPTY&, unsigned index, NonnullOwnPtr<KString> pts_name);
 
     RefPtr<MasterPTY> m_master;
     time_t m_time_of_last_write { 0 };
     unsigned m_index { 0 };
-    String m_tty_name;
+    NonnullOwnPtr<KString> m_tty_name;
 
     mutable IntrusiveListNode<SlavePTY> m_list_node;
 

Kernel/TTY/TTY.cpp

@@ -578,7 +578,7 @@ KResult TTY::ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg)
 
 KResultOr<NonnullOwnPtr<KString>> TTY::pseudo_path(const OpenFileDescription&) const
 {
-    return KString::try_create(tty_name());
+    return tty_name().try_clone();
 }
 
 void TTY::set_size(unsigned short columns, unsigned short rows)

Kernel/TTY/TTY.h

@@ -28,7 +28,7 @@ public:
     virtual KResult ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg) override final;
     virtual KResultOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const override;
 
-    virtual String const& tty_name() const = 0;
+    virtual KString const& tty_name() const = 0;
 
     unsigned short rows() const { return m_rows; }
     unsigned short columns() const { return m_columns; }

Kernel/TTY/VirtualConsole.cpp

@@ -103,7 +103,12 @@ void VirtualConsole::set_graphical(bool graphical)
 
 UNMAP_AFTER_INIT NonnullRefPtr<VirtualConsole> VirtualConsole::create(size_t index)
 {
-    auto virtual_console_or_error = DeviceManagement::try_create_device<VirtualConsole>(index);
+    // FIXME: Don't make a temporary String here
+    auto pts_name_or_error = KString::try_create(String::formatted("/dev/tty/{}", index));
+    VERIFY(!pts_name_or_error.is_error());
+    auto pts_name = pts_name_or_error.release_value();
+
+    auto virtual_console_or_error = DeviceManagement::try_create_device<VirtualConsole>(index, move(pts_name));
     // FIXME: Find a way to propagate errors
     VERIFY(!virtual_console_or_error.is_error());
     return virtual_console_or_error.release_value();
@@ -123,7 +128,6 @@ UNMAP_AFTER_INIT NonnullRefPtr<VirtualConsole> VirtualConsole::create_with_prese
 
 UNMAP_AFTER_INIT void VirtualConsole::initialize()
 {
-    m_tty_name = String::formatted("/dev/tty{}", m_index);
     VERIFY(GraphicsManagement::the().console());
     set_size(GraphicsManagement::the().console()->max_column(), GraphicsManagement::the().console()->max_row());
     m_console_impl.set_size(GraphicsManagement::the().console()->max_column(), GraphicsManagement::the().console()->max_row());
@@ -174,9 +178,10 @@ void VirtualConsole::refresh_after_resolution_change()
     flush_dirty_lines();
 }
 
-UNMAP_AFTER_INIT VirtualConsole::VirtualConsole(const unsigned index)
+UNMAP_AFTER_INIT VirtualConsole::VirtualConsole(const unsigned index, NonnullOwnPtr<KString> tty_name)
     : TTY(4, index)
     , m_index(index)
+    , m_tty_name(move(tty_name))
     , m_console_impl(*this)
 {
     initialize();

Kernel/TTY/VirtualConsole.h

@@ -86,13 +86,13 @@ public:
     void emit_char(char);
 
 private:
-    explicit VirtualConsole(const unsigned index);
+    explicit VirtualConsole(const unsigned index, NonnullOwnPtr<KString> tty_name);
     // ^KeyboardClient
     virtual void on_key_pressed(KeyEvent) override;
 
     // ^TTY
     virtual KResultOr<size_t> on_tty_write(const UserOrKernelBuffer&, size_t) override;
-    virtual String const& tty_name() const override { return m_tty_name; }
+    virtual KString const& tty_name() const override { return *m_tty_name; }
     virtual void echo(u8) override;
 
     // ^TerminalClient
@@ -114,7 +114,7 @@ private:
     bool m_active { false };
     bool m_graphical { false };
 
-    String m_tty_name;
+    NonnullOwnPtr<KString> m_tty_name;
 
 private:
     void initialize();