Add a test case that tickles a deadlock bug when migrating active source discs

tests/acceptance/active_migration_test/check.rb

@@ -0,0 +1,76 @@
+#!/usr/bin/env ruby
+require 'rubygems'
+require 'linux/nbd_client'
+require 'socket'
+require 'fileutils'
+
+Thread.abort_on_exception = true
+
+SIZE = 1024*1024*1024*10 # 10G
+WRITE_DATA = "foo!" * 2048 # 8K write
+
+puts "Cleaning up from old runs..."
+FileUtils.rm_f "src*"
+FileUtils.rm_f "dst*"
+
+puts "Creating source & destination files..."
+FileUtils.touch("src.file")
+File.truncate("src.file", SIZE)
+FileUtils.touch("dst.file")
+File.truncate("dst.file", SIZE)
+
+puts "Making filesystem on source..."
+result = Kernel.system "/sbin/mkfs.ext3 -F src.file" # some data to start with
+puts "Result of making filesystem: #{result.inspect}"
+
+puts "Starting destination process..."
+dst_proc = fork() {
+  exec("flexnbd listen -l 127.0.0.1 -p 9991 -f dst.file -s dst.sock -v >dst.stdout 2>dst.stderr")
+}
+
+puts "Starting source process..."
+src_proc = fork() {
+  exec("flexnbd serve -l 127.0.0.1 -p 9990 -f src.file -s src.sock -v >src.stdout 2>src.stderr")
+}
+
+puts "Sleeping to let flexnbds run..."
+sleep 10
+
+
+
+# Start writing to the source
+puts "Creating thread to write to the source..."
+src_writer = Thread.new do
+  client = Linux::NbdClient.new("127.0.0.1", 9990, true)
+  loop do
+    begin
+      client.write(0, WRITE_DATA)
+    rescue => err
+      puts "Writer encountered #{err.inspect} writing to source"
+      break
+    end
+  end
+end
+
+puts "Starting mirroring process..."
+UNIXSocket.open("src.sock") {|sock|
+  sock.write(["mirror", "127.0.0.1", "9991", "unlink"].join("\x0A") + "\x0A\x0A")
+  sock.flush
+  rsp = sock.readline
+  puts "Response: #{rsp}"
+}
+
+# tell serve to migrate to the listen one
+
+puts "Waiting for destination to exit..."
+dst_result = Process::waitpid2(dst_proc)
+puts "destination exited: #{dst_result.inspect}"
+
+puts "Waiting for source to exit..."
+src_result = Process::waitpid2(src_proc)
+puts "Source exited: #{src_result.inspect}"
+
+puts "Waiting for writer to die..."
+src_writer.join
+puts "Writer has died"
+