--- qemu-0.9.0.20070921/block.c.orig	2007-09-21 21:10:53.000000000 +0200
+++ qemu-0.9.0.20070921/block.c	2007-09-22 10:09:32.000000000 +0200
@@ -331,6 +331,7 @@
 
     if (flags & BDRV_O_SNAPSHOT) {
         BlockDriverState *bs1;
+        BlockDriver *drv1;
         int64_t total_size;
 
         /* if snapshot, we create a temporary backing file and open it
@@ -346,10 +347,22 @@
             return -1;
         }
         total_size = bdrv_getlength(bs1) >> SECTOR_BITS;
+        drv1 = bs1->drv;
         bdrv_delete(bs1);
 
         get_tmp_filename(tmp_filename, sizeof(tmp_filename));
-        realpath(filename, backing_filename);
+        /*
+         * for vvfat protocol the string "fat:<options>:" should remain
+         * the prefix of the filename even after realpath() call ...
+         */
+        if (drv1 == &bdrv_vvfat) {
+            int i = strrchr(filename, ':') - filename + 1;
+
+            strncpy(backing_filename, filename, i);
+            realpath(filename + i, backing_filename + i);
+        } else {
+            realpath(filename, backing_filename);
+        }
         if (bdrv_create(&bdrv_qcow2, tmp_filename,
                         total_size, backing_filename, 0) < 0) {
             return -1;