flexnbd: Move building the allocation map to before server socket bind()

Building the allocation map takes time, which scales with the size of the disc
being presented. By building that map in the space between bind() and accept(),
we leave the process in a useless state after the only good signal we have for
"we are ready" and the state where it is actually ready. This was breaking
migrations of large files.

src/serve.c

@@ -816,8 +816,8 @@ int do_serve(struct server* params)
 	int has_control;
 
 	error_set_handler((cleanup_handler*) serve_cleanup, params);
-	serve_open_server_socket(params);
 	serve_init_allocation_map(params);
+	serve_open_server_socket(params);
 	serve_accept_loop(params);
 	has_control = params->has_control;
 	serve_cleanup(params, 0);

tests/acceptance/flexnbd.rb

@@ -314,9 +314,16 @@ module FlexNBD
 
       while !File.socket?(ctrl)
         pid, status = Process.wait2(@pid, Process::WNOHANG)
-        raise "server did not start (#{cmd})" if pid
+        raise "server did not start (#{cmd}) - UNIX socket didn't appear" if pid
         sleep 0.1
       end
+
+      while !socket_open?
+        pid, status = Process.wait2(@pid, Process::WNOHANG)
+        raise "server did not start (#{cmd}) - TCP socket didn't appear" if pid
+        sleep 0.1
+      end
+
       at_exit { kill }
     end
     private :run_serve_cmd
@@ -511,7 +518,15 @@ module FlexNBD
       hsh
     end
 
+    def socket_open?
+      sock = (TCPSocket.new(@ip, @port) rescue nil)
+      !!sock
+    ensure
+      sock.close rescue nil if sock
+    end
+
 
   end
 
 end
+

tests/acceptance/flexnbd/fake_source.rb

@@ -8,16 +8,35 @@ module FlexNBD
   class FakeSource
 
     def initialize( addr, port, err_msg, source_addr=nil, source_port=0 )
-      timing_out( 2, err_msg ) do
-        @sock = if source_addr
-          TCPSocket.new( addr, port, source_addr, source_port )
+      timing_out( 10, err_msg ) {
+        @sock = wait_for_server_socket( addr, port, source_addr, source_port )
+      }
+    end
+
+
+    def wait_for_server_socket(addr, port, saddr = nil, sport = 0)
+      sock = nil
+
+      loop do
+        sock = try_get_server_socket( addr, port, saddr, sport )
+        break if sock
+        sleep 0.1
+      end
+
+      sock
+    end
+
+    def try_get_server_socket(addr, port, saddr = nil, sport = 0)
+      if saddr
+        TCPSocket.new( addr, port, saddr, sport ) rescue nil
       else
-          TCPSocket.new( addr, port )
-        end
+        TCPSocket.new( addr, port ) rescue nil
       end
     end
 
 
+
+
     def close
       @sock.close
     end
@@ -137,3 +156,4 @@ module FlexNBD
 
   end # class FakeSource
 end # module FlexNBD
+