Rework DiskDevice's read() and write() to be non-virtual wrappers.

This way subclasses only have to implement readBlock() and writeBlock().
read() and write() require that the offset and length are both divisible
by the blockSize().

VirtualFileSystem/DiskDevice.cpp

@@ -7,3 +7,39 @@ DiskDevice::DiskDevice()
 DiskDevice::~DiskDevice()
 {
 }
+
+bool DiskDevice::read(qword offset, unsigned length, byte* out) const
+{
+    ASSERT((offset % blockSize()) == 0);
+    ASSERT((length % blockSize()) == 0);
+    qword firstBlock = offset / blockSize();
+    qword endBlock = (offset + length) / blockSize();
+    ASSERT(firstBlock <= 0xffffffff);
+    ASSERT(endBlock <= 0xffffffff);
+    byte* outptr = out;
+    unsigned remainingCount = length;
+    for (unsigned bi = firstBlock; bi < endBlock; ++bi) {
+        if (!readBlock(bi, outptr))
+            return false;
+        outptr += blockSize();
+    }
+    return true;
+}
+
+bool DiskDevice::write(qword offset, unsigned length, const byte* in)
+{
+    ASSERT((offset % blockSize()) == 0);
+    ASSERT((length % blockSize()) == 0);
+    qword firstBlock = offset / blockSize();
+    qword endBlock = (offset + length) / blockSize();
+    ASSERT(firstBlock <= 0xffffffff);
+    ASSERT(endBlock <= 0xffffffff);
+    const byte* inptr = in;
+    for (unsigned bi = firstBlock; bi < endBlock; ++bi) {
+        if (!writeBlock(bi, inptr))
+            return false;
+        inptr += blockSize();
+    }
+    return true;
+}
+