Kernel: More work towards POSIX SHM, also add ftruncate().

Kernel/SharedMemory.cpp

@@ -0,0 +1,27 @@
+#include <Kernel/SharedMemory.h>
+#include <Kernel/VM/VMObject.h>
+
+SharedMemory::SharedMemory()
+{
+}
+
+SharedMemory::~SharedMemory()
+{
+}
+
+KResult SharedMemory::truncate(int length)
+{
+    if (!length) {
+        m_vmo = nullptr;
+        return KSuccess;
+    }
+
+    if (!m_vmo) {
+        m_vmo = VMObject::create_anonymous(length);
+        return KSuccess;
+    }
+
+    // FIXME: Support truncation.
+    ASSERT_NOT_REACHED();
+    return KResult(-ENOTIMPL);
+}