diff -r 80ea5f59f09a -r b421f396097a src/dev/storage/disk_image.hh
--- a/src/dev/storage/disk_image.hh	Thu Nov 26 10:03:43 2015 +0000
+++ b/src/dev/storage/disk_image.hh	Thu Nov 26 10:11:52 2015 +0000
@@ -82,6 +82,8 @@
     RawDiskImage(const Params *p);
     ~RawDiskImage();
 
+    void notifyFork() override;
+
     void close();
     void open(const std::string &filename, bool rd_only = false);
 
@@ -123,6 +125,8 @@
     CowDiskImage(const Params *p);
     ~CowDiskImage();
 
+    void notifyFork() override;
+
     void initSectorTable(int hash_size);
     bool open(const std::string &file);
     void save() const;
diff -r 80ea5f59f09a -r b421f396097a src/dev/storage/disk_image.cc
--- a/src/dev/storage/disk_image.cc	Thu Nov 26 10:03:43 2015 +0000
+++ b/src/dev/storage/disk_image.cc	Thu Nov 26 10:11:52 2015 +0000
@@ -65,6 +65,17 @@
 { close(); }
 
 void
+RawDiskImage::notifyFork()
+{
+    if (initialized && !readonly)
+        panic("Attempting to fork system with read-write raw disk image.");
+
+    const Params *p(dynamic_cast<const Params *>(params()));
+    close();
+    open(p->image_file, p->read_only);
+}
+
+void
 RawDiskImage::open(const string &filename, bool rd_only)
 {
     if (!filename.empty()) {
@@ -198,6 +209,16 @@
 }
 
 void
+CowDiskImage::notifyFork()
+{
+    if (!dynamic_cast<const Params *>(params())->read_only &&
+        !filename.empty()) {
+        inform("Disabling saving of COW image in forked child process.\n");
+        filename = "";
+    }
+}
+
+void
 SafeRead(ifstream &stream, void *data, int count)
 {
     stream.read((char *)data, count);
@@ -311,8 +332,12 @@
 void
 CowDiskImage::save() const
 {
-    save(filename);
-}
+    // filename will be set to the empty string to disable saving of
+    // the COW image in a forked child process. Save will still be
+    // called because there is no easy way to unregister the exit
+    // callback.
+    if (!filename.empty())
+        save(filename);}
 
 void
 CowDiskImage::save(const string &file) const