lxc-exporter/lib/ns.rb

require 'fiddle'
require 'fiddle/import'
require 'io/extra'

class NS
  extend Fiddle::Importer
  dlload Fiddle.dlopen( nil)
  SetNS_Function = Fiddle::Function.new handler['setns'], [Fiddle::TYPE_VOIDP, Fiddle::TYPE_VOIDP], Fiddle::TYPE_INT

  class <<self
    def setns fd, t
      r = SetNS_Function.call fd.to_i, t.to_i
      SystemCallError.new "setns(#{fd.to_i})", Fiddle.last_error  if -1 == r
      r
    end

    def _open_nsfd pid, type
      File.open "/proc/%d/ns/%s" % [pid, type]
    end

    def open pid, *types, &exe
      ns = new pid, *types
      if block_given?
        begin yield ns
        ensure ns.close
        end
      else ns
      end
    end

    def change pid, *types, &exe
      open pid, *types do |ns|
        ns.change &exe
      end
    end

    def enter pid, keep_open: nil
      new( pid).enter keep_open: keep_open
    end
  end

  attr_reader :pid, :fds

  def initialize pid, *types
    @pid, @fds = pid, {}
    types = Dir.children "/proc/%d/ns" % pid  if types.empty? or types.include?( :any)
    types.each {|t| @fds[t.to_sym] = self.class._open_nsfd pid, t }
  end

  def close_ios *keep_open
    keep_open =
      keep_open.flatten.map do |fd|
        case fd
        when Integer then fd
        when IO then fd.to_i
        when nil # ignore
        else raise ArgumentError, "Unknown file descriptor for keeping opened: #{fd.inspect}"
        end
      end.sort
    IO.fdwalk(0) {|fd| fd.close  unless keep_open.include? fd.to_i }
  end

  def enter keep_open: nil
    close_ios keep_open, @fds.values
    @fds.each {|_, fd| self.class.setns fd, 0 }
    close
    nil
  end

  def close
    @fds.each {|_, fd| fd.close }
  end

  def change &block
    if block_given?
      @owns = @fds.map {|ns, _f| self.class._open_nsfd $$, ns }
      begin
        @fds.each {|type, fd| self.class.setns fd, 0 }
        yield
      ensure
        @owns.each {|fd| self.class.setns fd, 0 }
      end
    else
      @fds.each {|type, fd| self.class.setns fd, 0 }
      nil
    end
  end
end