From d2046e79cfd915429b4755ef8e1338a1baa7815f Mon Sep 17 00:00:00 2001
From: Andreas Kling <awesomekling@gmail.com>
Date: Fri, 16 Nov 2018 17:56:18 +0100
Subject: [PATCH] Add a DoubleBuffer thingy to allow TTY read/write to be
 interleaved.

I feel like this concept might be useful in more places. It's very naive
right now and uses dynamically growing buffers. It should really use static
size buffers and never kmalloc().
---
 AK/Vector.h    |  8 ++++++++
 Kernel/TTY.cpp | 42 +++++++++++++++++++++++++++++++-----------
 Kernel/TTY.h   | 25 ++++++++++++++++++++++++-
 3 files changed, 63 insertions(+), 12 deletions(-)

diff --git a/AK/Vector.h b/AK/Vector.h
index 8824e10a46..d52cea64e2 100644
--- a/AK/Vector.h
+++ b/AK/Vector.h
@@ -188,6 +188,14 @@ public:
         ++m_impl->m_size;
     }
 
+    void append(const T* values, size_t count)
+    {
+        ensureCapacity(size() + count);
+        for (size_t i = 0; i < count; ++i)
+            new (m_impl->slot(m_impl->m_size + i)) T(values[i]);
+        m_impl->m_size += count;
+    }
+
     void ensureCapacity(size_t neededCapacity)
     {
         if (capacity() >= neededCapacity)
diff --git a/Kernel/TTY.cpp b/Kernel/TTY.cpp
index 754bef3f52..fca09c7f00 100644
--- a/Kernel/TTY.cpp
+++ b/Kernel/TTY.cpp
@@ -4,6 +4,32 @@
 #include <LibC/signal_numbers.h>
 #include <LibC/sys/ioctl_numbers.h>
 
+void DoubleBuffer::flip()
+{
+    ASSERT(m_read_buffer_index == m_read_buffer->size());
+    swap(m_read_buffer, m_write_buffer);
+    m_write_buffer->clear();
+    m_read_buffer_index = 0;
+}
+
+Unix::ssize_t DoubleBuffer::write(const byte* data, size_t size)
+{
+    m_write_buffer->append(data, size);
+    return size;
+}
+
+Unix::ssize_t DoubleBuffer::read(byte* data, size_t size)
+{
+    if (m_read_buffer_index >= m_read_buffer->size() && !m_write_buffer->isEmpty())
+        flip();
+    if (m_read_buffer_index >= m_read_buffer->size())
+        return 0;
+    ssize_t nread = min(m_read_buffer->size() - m_read_buffer_index, size);
+    memcpy(data, m_read_buffer->data() + m_read_buffer_index, nread);
+    m_read_buffer_index += nread;
+    return nread;
+}
+
 TTY::TTY(unsigned major, unsigned minor)
     : CharacterDevice(major, minor)
 {
@@ -17,15 +43,7 @@ TTY::~TTY()
 
 ssize_t TTY::read(byte* buffer, size_t size)
 {
-    ssize_t nread = min(m_buffer.size(), size);
-    memcpy(buffer, m_buffer.data(), nread);
-    if (nread == (ssize_t)m_buffer.size())
-        m_buffer.clear();
-    else {
-        kprintf("had %u, read %u\n", m_buffer.size(), nread);
-        ASSERT_NOT_REACHED();
-    }
-    return nread;
+    return m_buffer.read(buffer, size);
 }
 
 ssize_t TTY::write(const byte* buffer, size_t size)
@@ -36,12 +54,12 @@ ssize_t TTY::write(const byte* buffer, size_t size)
 
 bool TTY::hasDataAvailableForRead() const
 {
-    return !m_buffer.isEmpty();
+    return !m_buffer.is_empty();
 }
 
 void TTY::emit(byte ch)
 {
-    m_buffer.append(ch);
+    m_buffer.write(&ch, 1);
 }
 
 void TTY::interrupt()
@@ -93,6 +111,8 @@ int TTY::ioctl(Process& process, unsigned request, unsigned arg)
         *tp = m_termios;
         return 0;
     case TCSETS:
+    case TCSETSF:
+    case TCSETSW:
         tp = reinterpret_cast<Unix::termios*>(arg);
         if (!process.validate_read(tp, sizeof(Unix::termios)))
             return -EFAULT;
diff --git a/Kernel/TTY.h b/Kernel/TTY.h
index 8018012ce0..b1a45ab9a2 100644
--- a/Kernel/TTY.h
+++ b/Kernel/TTY.h
@@ -5,6 +5,29 @@
 
 class Process;
 
+class DoubleBuffer {
+public:
+    DoubleBuffer()
+        : m_write_buffer(&m_buffer1)
+        , m_read_buffer(&m_buffer2)
+    {
+    }
+
+    Unix::ssize_t write(const byte*, size_t);
+    Unix::ssize_t read(byte*, size_t);
+
+    bool is_empty() const { return m_read_buffer_index >= m_read_buffer->size() && m_write_buffer->isEmpty(); }
+
+private:
+    void flip();
+
+    Vector<byte>* m_write_buffer { nullptr };
+    Vector<byte>* m_read_buffer { nullptr };
+    Vector<byte> m_buffer1;
+    Vector<byte> m_buffer2;
+    size_t m_read_buffer_index { 0 };
+};
+
 class TTY : public CharacterDevice {
 public:
     virtual ~TTY() override;
@@ -35,7 +58,7 @@ protected:
     void interrupt();
 
 private:
-    Vector<byte> m_buffer;
+    DoubleBuffer m_buffer;
     pid_t m_pgid { 0 };
     Unix::termios m_termios;
 };