Kernel: Move TTY-related code to a new subdirectory under Devices

The TTY subsystem is represented with unix devices, so it should be
under the Devices directory like the Audio, Storage, GPU and HID
subsystems.

Kernel/Devices/TTY/MasterPTY.cpp

@@ -0,0 +1,134 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/API/Ioctl.h>
+#include <Kernel/API/POSIX/errno.h>
+#include <Kernel/API/POSIX/signal_numbers.h>
+#include <Kernel/Debug.h>
+#include <Kernel/Devices/TTY/MasterPTY.h>
+#include <Kernel/Devices/TTY/PTYMultiplexer.h>
+#include <Kernel/Devices/TTY/SlavePTY.h>
+#include <Kernel/Interrupts/InterruptDisabler.h>
+#include <Kernel/Tasks/Process.h>
+
+namespace Kernel {
+
+ErrorOr<NonnullLockRefPtr<MasterPTY>> MasterPTY::try_create(unsigned int index)
+{
+    auto buffer = TRY(DoubleBuffer::try_create("MasterPTY: Buffer"sv));
+    auto master_pty = TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) MasterPTY(index, move(buffer))));
+    auto credentials = Process::current().credentials();
+    auto slave_pty = TRY(adopt_nonnull_lock_ref_or_enomem(new (nothrow) SlavePTY(*master_pty, credentials->uid(), credentials->gid(), index)));
+    master_pty->m_slave = slave_pty;
+    TRY(master_pty->after_inserting());
+    TRY(slave_pty->after_inserting());
+    return master_pty;
+}
+
+MasterPTY::MasterPTY(unsigned index, NonnullOwnPtr<DoubleBuffer> buffer)
+    : CharacterDevice(200, index)
+    , m_index(index)
+    , m_buffer(move(buffer))
+{
+    m_buffer->set_unblock_callback([this]() {
+        if (m_slave)
+            evaluate_block_conditions();
+    });
+}
+
+MasterPTY::~MasterPTY()
+{
+    dbgln_if(MASTERPTY_DEBUG, "~MasterPTY({})", m_index);
+    PTYMultiplexer::the().notify_master_destroyed({}, m_index);
+}
+
+ErrorOr<size_t> MasterPTY::read(OpenFileDescription&, u64, UserOrKernelBuffer& buffer, size_t size)
+{
+    if (!m_slave && m_buffer->is_empty())
+        return 0;
+    return m_buffer->read(buffer, size);
+}
+
+ErrorOr<size_t> MasterPTY::write(OpenFileDescription&, u64, UserOrKernelBuffer const& buffer, size_t size)
+{
+    if (!m_slave)
+        return EIO;
+    m_slave->on_master_write(buffer, size);
+    return size;
+}
+
+bool MasterPTY::can_read(OpenFileDescription const&, u64) const
+{
+    if (!m_slave)
+        return true;
+    return !m_buffer->is_empty();
+}
+
+bool MasterPTY::can_write(OpenFileDescription const&, u64) const
+{
+    return true;
+}
+
+void MasterPTY::notify_slave_closed(Badge<SlavePTY>)
+{
+    dbgln_if(MASTERPTY_DEBUG, "MasterPTY({}): slave closed, my retains: {}, slave retains: {}", m_index, ref_count(), m_slave->ref_count());
+    // +1 ref for my MasterPTY::m_slave
+    // +1 ref for OpenFileDescription::m_device
+    if (m_slave->ref_count() == 2)
+        m_slave = nullptr;
+}
+
+ErrorOr<size_t> MasterPTY::on_slave_write(UserOrKernelBuffer const& data, size_t size)
+{
+    if (m_closed)
+        return EIO;
+    return m_buffer->write(data, size);
+}
+
+bool MasterPTY::can_write_from_slave() const
+{
+    if (m_closed)
+        return true;
+    return m_buffer->space_for_writing() >= 2;
+}
+
+ErrorOr<void> MasterPTY::close()
+{
+    InterruptDisabler disabler;
+    // After the closing OpenFileDescription dies, slave is the only thing keeping me alive.
+    // From this point, let's consider ourselves closed.
+    m_closed = true;
+
+    if (m_slave)
+        m_slave->hang_up();
+
+    return {};
+}
+
+ErrorOr<void> MasterPTY::ioctl(OpenFileDescription& description, unsigned request, Userspace<void*> arg)
+{
+    TRY(Process::current().require_promise(Pledge::tty));
+    if (!m_slave)
+        return EIO;
+    switch (request) {
+    case TIOCGPTN: {
+        int master_pty_index = index();
+        return copy_to_user(static_ptr_cast<int*>(arg), &master_pty_index);
+    }
+    case TIOCSWINSZ:
+    case TIOCGPGRP:
+        return m_slave->ioctl(description, request, arg);
+    default:
+        return EINVAL;
+    }
+}
+
+ErrorOr<NonnullOwnPtr<KString>> MasterPTY::pseudo_path(OpenFileDescription const&) const
+{
+    return KString::formatted("ptm:{}", m_index);
+}
+
+}