Tidy up ld preload hacks

tests/acceptance/ld_preload.rb

@@ -0,0 +1,36 @@
+require 'tempfile'
+
+# LdPreload is a little wrapper for using LD_PRELOAD when testing flexnbd
+module LdPreload
+  # This takes an object name, sets up a temporary log file, whose name is
+  # recorded in the environment as OUTPUT_obj_name, where obj_name is the
+  # name of the preload module to build and load.
+  def with_ld_preload(obj_name)
+    @ld_preload_logs ||= {}
+    flunk 'Can only load a preload module once!' if @ld_preload_logs[obj_name]
+
+    system("make -C ld_preloads/ #{obj_name}.o > /dev/null") ||
+      flunk("Failed to build object #{obj_name}")
+    orig_env = ENV['LD_PRELOAD']
+    ENV['LD_PRELOAD'] = [orig_env, File.expand_path("./ld_preloads/#{obj_name}.o")].compact.join(' ')
+
+    # Open the log, and stick it in a hash
+    @ld_preload_logs[obj_name] = Tempfile.new(obj_name)
+    ENV['OUTPUT_' + obj_name] = @ld_preload_logs[obj_name].path
+
+    yield
+  ensure
+    if @ld_preload_logs[obj_name]
+      @ld_preload_logs[obj_name].close
+      @ld_preload_logs.delete(obj_name)
+    end
+    ENV['LD_PRELOAD'] = orig_env
+  end
+
+  def read_ld_preload_log(obj_name)
+    lines = []
+    lines << @ld_preload_logs[obj_name].readline.chomp until
+      @ld_preload_logs[obj_name].eof?
+    lines
+  end
+end