Improved fuzz test to find an actual code bug (previous bug was in the test

<g>).

tests/flexnbd.rb

@@ -7,7 +7,7 @@ class FlexNBD
 
   def initialize(bin, ip, port)
     @bin  = bin
-    @debug = `#{@bin} serve --help` =~ /--debug/ ? "--debug" : ""
+    @debug = "--verbose" # tests always run in debug mode!
     @valgrind = ENV['VALGRIND'] ? "valgrind " : ""
     @bin = "#{@valgrind}#{@bin}"
     raise "#{bin} not executable" unless File.executable?(bin)
@@ -25,6 +25,7 @@ class FlexNBD
          "--sock #{ctrl} "\
          "#{@debug} "\
          "#{acl.join(' ')}"
+    #STDERR.print "#{cmd}\n"
     @pid = fork do
       exec(cmd)
     end
@@ -42,15 +43,17 @@ class FlexNBD
   end
 
   def read(offset, length)
-    IO.popen("#{@bin} read "\
+    
+    out = IO.popen("#{@bin} read "\
              "--addr #{ip} "\
              "--port #{port} "\
              "--from #{offset} "\
              "#{@debug} "\
              "--size #{length}","r") do |fh|
-      return fh.read
+      fh.read
     end
-    raise "read failed" unless $?.success?
+    raise IOError.new "NBD read failed" unless $?.success?
+    out
   end
 
   def write(offset, data)
@@ -62,7 +65,7 @@ class FlexNBD
              "--size #{data.length}","w") do |fh|
       fh.write(data)
     end
-    raise "write failed" unless $?.success?
+    raise IOError.new "NBD write failed" unless $?.success?
     nil
   end
 

tests/fuzz

@@ -22,7 +22,7 @@ end
 testname_local = "#{$0}.test.#{$$}.local"
 testname_serve = "#{$0}.test.#{$$}.serve"
 [testname_local, testname_serve].each do |name|
-  File.open(name, "w+") { |fh| fh.seek(test_size-1, IO::SEEK_SET); fh.write("0") }
+  File.open(name, "w+") { |fh| fh.seek(test_size-1, IO::SEEK_SET); fh.write("\0") }
 end
 
 @local = File.open(testname_local, "r+")
@@ -55,15 +55,22 @@ repetitions.times do |n|
     length &= 0xfffff000 if CHEAT_AND_ROUND_DOWN
     offset = rand(test_size - length)
     offset &= 0xfffff000 if CHEAT_AND_ROUND_DOWN
-    content = (n%2 == 1) ? ("x" * length) : ("\0" * length)
+    
+    content = (n%2 == 0) ? ("\0" * length) : ( ((n/2)&255).chr * length)
         
     @local.seek(offset, IO::SEEK_SET)
     @local.write(content)
+    @local.fsync
   
     @serve.write(offset, content)
   
-    if @serve.read(offset, length) != content
+    check_read = @serve.read(offset, length)
-      STDERR.print "After pass #{n}: Didn't read back what we wrote!"
+    if check_read != content
+      STDERR.print "After pass #{n}: Didn't read back what we wrote!\n"
+      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"
+      IO.popen("hexdump", "w") { |io| io.print(check_read) }
       exit 1
     end