Add a PTY multiplexer (/dev/ptmx) device.

When you open /dev/ptmx, you get a file descriptor pointing to one of the
available MasterPTY's. If none are available, you get an EBUSY.

This makes it possible to open multiple (up to 4) Terminals. :^)

To support this, I also added a CharacterDevice::open() that gets control
when VFS is opening a CharacterDevice. This is useful when we want to return
a custom FileDescriptor like we do here.

1 files changed, 27 insertions, 0 deletions

diff --git a/Kernel/PTYMultiplexer.cpp b/Kernel/PTYMultiplexer.cpp
new file mode 100644
index 0000000000..26403e898c
--- /dev/null
+++ b/Kernel/PTYMultiplexer.cpp
@@ -0,0 +1,27 @@
+#include "PTYMultiplexer.h"
+#include "MasterPTY.h"
+#include <LibC/errno_numbers.h>
+
+PTYMultiplexer::PTYMultiplexer()
+    : CharacterDevice(5, 2)
+{
+    m_freelist.ensureCapacity(4);
+    for (int i = 4; i > 0; --i)
+        m_freelist.unchecked_append(adopt(*new MasterPTY(i - 1)));
+}
+
+PTYMultiplexer::~PTYMultiplexer()
+{
+}
+
+RetainPtr<FileDescriptor> PTYMultiplexer::open(int& error, int options)
+{
+    LOCKER(m_lock);
+    if (m_freelist.is_empty()) {
+        error = -EBUSY;
+        return nullptr;
+    }
+    auto master = m_freelist.takeLast();
+    dbgprintf("PTYMultiplexer::open: Vending master %u\n", master->index());
+    return VFS::the().open(move(master), error, options);
+}