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/FileBackedDiskDevice.cpp

@@ -0,0 +1,82 @@
+#define _FILE_OFFSET_BITS 64
+
+#include "FileBackedDiskDevice.h"
+#include <cstring>
+#include <sys/stat.h>
+
+//#define FBBD_DEBUG
+#define IGNORE_FILE_LENGTH // Useful for e.g /dev/hda2
+
+RetainPtr<FileBackedDiskDevice> FileBackedDiskDevice::create(String&& imagePath, unsigned blockSize)
+{
+    return adopt(*new FileBackedDiskDevice(std::move(imagePath), blockSize));
+}
+
+FileBackedDiskDevice::FileBackedDiskDevice(String&& imagePath, unsigned blockSize)
+    : m_imagePath(std::move(imagePath))
+    , m_blockSize(blockSize)
+{
+    struct stat st;
+    int result = stat(m_imagePath.characters(), &st);
+    ASSERT(result != -1);
+    m_fileLength = st.st_size;
+    m_file = fopen(m_imagePath.characters(), "r+");
+}
+
+FileBackedDiskDevice::~FileBackedDiskDevice()
+{
+}
+
+unsigned FileBackedDiskDevice::blockSize() const
+{
+    return m_blockSize;
+}
+
+bool FileBackedDiskDevice::readBlock(unsigned index, byte* out) const
+{
+    qword offset = index * m_blockSize;
+    return read(offset, blockSize(), out);
+}
+
+bool FileBackedDiskDevice::writeBlock(unsigned index, const byte* data)
+{
+    qword offset = index * m_blockSize;
+    return write(offset, blockSize(), data);
+}
+
+bool FileBackedDiskDevice::read(qword offset, unsigned length, byte* out) const
+{
+#ifndef IGNORE_FILE_LENGTH
+    if (offset + length >= m_fileLength)
+        return false;
+#endif
+#ifdef FBBD_DEBUG
+    printf("[FileBackedDiskDevice] Read device @ offset %llx, length %u\n", offset, length);
+#endif
+    fseeko(m_file, offset, SEEK_SET);
+    unsigned nread = fread(out, sizeof(byte), length, m_file);
+    ASSERT(nread == length);
+    return true;
+}
+
+bool FileBackedDiskDevice::write(qword offset, unsigned length, const byte* data)
+{
+#ifndef IGNORE_FILE_LENGTH
+    if (offset + length >= m_fileLength)
+        return false;
+#endif
+#ifdef FBBD_DEBUG
+    printf("[FileBackedDiskDevice] Write device @ offset %llx, length %u\n", offset, length);
+#endif
+    fseeko(m_file, offset, SEEK_SET);
+    // size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream);
+    unsigned nwritten = fwrite(data, sizeof(byte), length, m_file);
+    ASSERT(nwritten == length);
+    return true;
+}
+
+const char* FileBackedDiskDevice::className() const
+{
+    return "FileBackedDiskDevice";
+}
+