BlockDevice -> DiskDevice.

BlockDevice was the wrong name for this abstraction, since a block device
is a type of file in a unix system, and we should use that name for that
concept in the fs implementation.

VirtualFileSystem/DiskBackedFileSystem.cpp

@@ -0,0 +1,78 @@
+#include "DiskBackedFileSystem.h"
+
+//#define DBFS_DEBUG
+
+DiskBackedFileSystem::DiskBackedFileSystem(RetainPtr<DiskDevice>&& device)
+    : m_device(std::move(device))
+{
+    ASSERT(m_device);
+}
+
+DiskBackedFileSystem::~DiskBackedFileSystem()
+{
+}
+
+bool DiskBackedFileSystem::writeBlock(unsigned index, const ByteBuffer& data)
+{
+    ASSERT(data.size() == blockSize());
+#ifdef DBFS_DEBUG
+    printf("DiskBackedFileSystem::writeBlock %u\n", index);
+#endif
+    qword baseOffset = static_cast<qword>(index) * static_cast<qword>(blockSize());
+    return device().write(baseOffset, blockSize(), data.pointer());
+}
+
+bool DiskBackedFileSystem::writeBlocks(unsigned index, unsigned count, const ByteBuffer& data)
+{
+#ifdef DBFS_DEBUG
+    printf("DiskBackedFileSystem::writeBlocks %u x%u\n", index, count);
+#endif
+    qword baseOffset = static_cast<qword>(index) * static_cast<qword>(blockSize());
+    return device().write(baseOffset, count * blockSize(), data.pointer());
+}
+
+ByteBuffer DiskBackedFileSystem::readBlock(unsigned index) const
+{
+#ifdef DBFS_DEBUG
+    printf("DiskBackedFileSystem::readBlock %u\n", index);
+#endif
+    auto buffer = ByteBuffer::createUninitialized(blockSize());
+    qword baseOffset = static_cast<qword>(index) * static_cast<qword>(blockSize());
+    auto* bufferPointer = buffer.pointer();
+    device().read(baseOffset, blockSize(), bufferPointer);
+    ASSERT(buffer.size() == blockSize());
+    return buffer;
+}
+
+ByteBuffer DiskBackedFileSystem::readBlocks(unsigned index, unsigned count) const
+{
+    if (!count)
+        return nullptr;
+    if (count == 1)
+        return readBlock(index);
+    auto blocks = ByteBuffer::createUninitialized(count * blockSize());
+    byte* out = blocks.pointer();
+
+    for (unsigned i = 0; i < count; ++i) {
+        auto block = readBlock(index + i);
+        if (!block)
+            return nullptr;
+        memcpy(out, block.pointer(), block.size());
+        out += blockSize();
+    }
+
+    return blocks;
+}
+
+void DiskBackedFileSystem::setBlockSize(unsigned blockSize)
+{
+    if (blockSize == m_blockSize)
+        return;
+    m_blockSize = blockSize;
+    invalidateCaches();
+}
+
+void DiskBackedFileSystem::invalidateCaches()
+{
+    // FIXME: Implement block cache.
+}