Try to preserve sparse files when dumping with no compression

Implemented by Thomas Wagner <wagner-thomas@gmx.at>

virt-backup

@@ -584,8 +584,16 @@ sub run_dump{
                 $cmd .= " | $dumpcmd 2>/dev/null";
             }
 	    else {
-                print "\nStarting dump of $source to $dest\n\n" if ($opts{debug});
-                $cmd = "$opts{ionice} dd if=$source bs=$opts{blocksize} | $opts{nice} $opts{compcmd} > $dest 2>/dev/null";
+		if ( -f $source && $opts{compcmd} eq 'cat' ){
+                    # Source disk is a regular file and no compression was selected
+                    # thus use cp instead of dd to preserve possible sparsity
+                    print "\nStarting dump of $source to $dest using cp -a\n\n" if ($opts{debug});
+                    $cmd = "$opts{ionice} cp -a $source $dest";
+                }
+                else {
+                    print "\nStarting dump of $source to $dest using dd\n\n" if ($opts{debug});
+                    $cmd = "$opts{ionice} dd if=$source bs=$opts{blocksize} | $opts{nice} $opts{compcmd} > $dest 2>/dev/null";
+                }
             }
         }
         unless( system("$cmd") == 0 ){