Added some record-keeping / printing to fuzzer to assist with backtracking.

tests/fuzz

@@ -30,6 +30,13 @@ end
 @serve = FlexNBD.new(binary, "127.0.0.1", 41234)
 @serve.serve(testname_serve)
 
+$record = []
+def print_record
+  $record.each do |offset, length, byte|
+    STDERR.print "  wrote #{byte} to #{offset}+#{length}\n"
+  end
+end
+
 repetitions.times do |n|
 
   begin
@@ -44,6 +51,7 @@ repetitions.times do |n|
   
     if md5_local != md5_serve
       STDERR.print "Before pass #{n}: MD5 error: local=#{md5_local} serve=#{md5_serve}\n"
+      print_record
       STDERR.print "**** Local contents:\n"
       system("hexdump #{testname_local}")
       STDERR.print "**** Serve contents:\n"
@@ -51,12 +59,14 @@ repetitions.times do |n|
       exit 1
     end
 
-    length = rand(max_length)
+    length = rand(max_length/8)
     length &= 0xfffff000 if CHEAT_AND_ROUND_DOWN
     offset = rand(test_size - length)
     offset &= 0xfffff000 if CHEAT_AND_ROUND_DOWN
     
-    content = (n%2 == 0) ? ("\0" * length) : ( ((n/2)&255).chr * length)
+    content = (n%2 == 0) ? ("\0" * length) : ( (n&255).chr * length)
+    
+    $record << [offset, length, content[0]]
         
     @local.seek(offset, IO::SEEK_SET)
     @local.write(content)
@@ -67,6 +77,7 @@ repetitions.times do |n|
     check_read = @serve.read(offset, length)
     if check_read != content
       STDERR.print "After pass #{n}: Didn't read back what we wrote!\n"
+      print_record
       STDERR.print "*** We wrote these #{content.length} bytes...\n"
       IO.popen("hexdump", "w") { |io| io.print(content) }
       STDERR.print "*** But we got back these #{check_read.length} bytes...\n"
@@ -76,6 +87,7 @@ repetitions.times do |n|
     
   rescue StandardError => ex
     STDERR.print "During pass #{n}: Exception: #{ex}"
+      print_record
     STDERR.print ex.backtrace.join("\n") + "\n"
     exit 2
   end