Changeset 14910 in vbox

Timestamp:

Dec 2, 2008 3:14:24 PM (16 years ago)

Author:

vboxsync

Message:

Storage/VHD: comment change, documenting why the current code works for diff images. Tiny cleanup to be on the safe side, signalling that no extra data is needed.

File:

• trunk/src/VBox/Devices/Storage/VHDHDDCore.cpp (modified) (2 diffs)

trunk/src/VBox/Devices/Storage/VHDHDDCore.cpp

@@ -1021 +1021 @@
         /*
          * If the block is not allocated the content of the entry is ~0
-         * and we need to allocate a new block.
+         * and we need to allocate a new block. Note that while blocks are
+         * allocated with a relatively big granularity, each sector has its
+         * own bitmap entry, indicating whether it has been written or not.
+         * So that means for the purposes of the higher level that the
+         * granularity is invisible.
          */
-        /** @todo Integrate this properly into the unallocated block logic.
-         * The current code wouldn't be able to handle diff images at all. */
         if (pImage->pBlockAllocationTable[cBlockAllocationTableEntry] == ~0U)
         {
@@ -1087 +1089 @@
     if (pcbWriteProcess)
         *pcbWriteProcess = cbToWrite;
+
+    /* Stay on the safe side. Do not run the risk of confusing the higher
+     * level, as that can be pretty lethal to image consistency. */
+    *pcbPreRead = 0;
+    *pcbPostRead = 0;
 
     return rc;