rtnl: ifinfmsg: symbolic flags improvement

Now the mask (`change`) is calculated automatically,
and to clean the flag one can provide it in a simple
'!FLAG' notation:

```
ip.link('set', index=dev, flags=['IFF_UP'])
ip.link('set', index=dev, flags=['!IFF_UP'])
```

Bug-Url: #69

pyroute2/netlink/rtnl/ifinfmsg.py

@@ -23,6 +23,8 @@
 IFF_DORMANT = 0x20000 # driver signals dormant
 IFF_ECHO = 0x40000 # echo sent packets
 
+(IFF_NAMES, IFF_VALUES) = map_namespace('IFF', globals())
+
 IFF_MASK = IFF_UP |\
  IFF_DEBUG |\
  IFF_NOTRAILERS |\
@@ -40,8 +42,6 @@
  IFF_LOWER_UP |\
  IFF_DORMANT
 
-(IFF_NAMES, IFF_VALUES) = map_namespace('IFF', globals())
-
 states = ('UNKNOWN',
  'NOTPRESENT',
  'DOWN',
@@ -131,24 +131,29 @@ class ifinfmsg(nlmsg):
  ('IFLA_NUM_RX_QUEUES', 'uint32'))
 
  @staticmethod
- def flags2names(flags):
+ def flags2names(flags, mask=0xffffffff):
  ret = []
  for flag in IFF_VALUES:
- if flag & flags:
+ if (flag & mask & flags) == flag:
  ret.append(IFF_VALUES[flag])
  return ret
 
  @staticmethod
  def names2flags(flags):
  ret = 0
+ mask = 0
  for flag in flags:
- ret |= IFF_NAMES[flag]
- return ret
+ if flag[0] == '!':
+ flag = flag[1:]
+ else:
+ ret |= IFF_NAMES[flag]
+ mask |= IFF_NAMES[flag]
+ return (ret, mask)
 
  def encode(self):
  # convert flags
  if isinstance(self['flags'], (set, tuple, list)):
- self['flags'] = self.names2flags(self['flags'])
+ self['flags'], self['change'] = self.names2flags(self['flags'])
  return nlmsg.encode(self)
 
  class wireless(iw_event):

tests/test_ipr.py

@@ -279,6 +279,14 @@ def test_route_table_2048(self):
  pattern='172.16.1.0/24.*172.16.0.1')
  remove_link('bala')
 
+ def test_symbolic_flags(self):
+ require_user('root')
+ dev = self.dev[0]
+ self.ip.link('set', index=dev, flags=['IFF_UP'])
+ assert self.ip.get_links(dev)[0]['flags'] & 1
+ self.ip.link('set', index=dev, flags=['!IFF_UP'])
+ assert not (self.ip.get_links(dev)[0]['flags'] & 1)
+
  def test_updown_link(self):
  require_user('root')
  dev = self.dev[0]