Expose named caches as dimensions.

appengine/swarming/swarming_bot/api/os_utilities.py

Index: appengine/swarming/swarming_bot/api/os_utilities.py
diff --git a/appengine/swarming/swarming_bot/api/os_utilities.py b/appengine/swarming/swarming_bot/api/os_utilities.py
index 28710d916c0135d0bbd602314a48aaca87677906..202f565f45ffbee336c3914b514f517f390edd49 100644
--- a/appengine/swarming/swarming_bot/api/os_utilities.py
+++ b/appengine/swarming/swarming_bot/api/os_utilities.py
@@ -1,3 +1,4 @@
+# coding: utf-8
 # Copyright 2014 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
@@ -514,6 +515,30 @@ def get_uptime():
   return platforms.linux.get_uptime()
 
 
+def get_named_caches():
+  """Returns the list of named caches."""
+  # Strictly speaking, this is a layering violation. This data is managed by
+  # run_isolated.py but this is valuable to expose this as a Swarming bot
+  # dimensions so ¯\_(ツ)_/¯
+  #
+  # Assumptions:
+  # - ../__main__.py calls os.chdir(__file__)
+  # - ../bot_code/bot_main.py specifies
+  #   --named-cache-root os.path.join(botobj.base_dir, 'c') to run_isolated.
+  # - ../client/named_cache.py behavior
+  #
+  # A better implementation would require:
+  # - Access to bot.Bot instance to query bot.base_dir
+  # - Access to named_cache.py to load state.json
+  # - Access to --named-cache-root hardcoded in bot_main.py
+  #
+  # but hey, the following code is 4 lines...
+  d = os.path.join(os.getcwd(), u'c', u'named')

[nodir, 2017/05/31 16:52:06]

"named" symlinks are best effort. Better not to put them to the critical path.

Can we read c/state.json here instead? the code would be still simple

[M-A Ruel, 2017/05/31 20:45:32]

Then maybe we shouldn't create them. :/
Either we ensure the symlinks are good when cleanup() is called, either we drop
them, I prefer to not keep mostly-works paths.
Done.

[nodir, 2017/05/31 21:03:21]

we keep them for troopers and alike. My point is that it is not fatal to fail to
create a symlink, for example.

+  if not os.path.isdir(d):
+    return []
+  return [i for i in os.listdir(d)]
+
+
 class AuthenticatedHttpRequestFailure(Exception):
   pass
 
@@ -849,6 +874,9 @@ def get_dimensions():
     u'os': [os_name],
     u'pool': [u'default'],
   }
+  caches = get_named_caches()
+  if caches:
+    dimensions[u'caches'] = caches
   if u'avx2' in cpuinfo.get(u'flags', []):
     dimensions[u'cpu'].append(cpu_type + u'-' + cpu_bitness + u'-avx2')
   if any(u'avx512' in x for x in cpuinfo.get(u'flags', [])):