Add capabilities to storage driver

Storage capabilities is used to indicate the static and dynamic ability
of the storage driver object based on current driver implementation or
particular driver configuration and backend status.

Use storage capabilities glance_store can do more proper operations on
backend to support upper layer request, like to enable or disable add()
function to glance, or if allow glance reuse driver instance for all
request according to whether the driver and/or backend is stateless.

This patch implemented some initial capabilities for existing drivers,
and change the foundational code to make them be aware. Mainly it
contains:

1. Implemented essential code to enable driver capabilities, adding
necessary capabilities.

2. Added a generic checker on necessary storage operations, to make sure
the capabilities of the driver are capable of handling requested
operation. We can enhance the check logic as needed easily in future.

3. Added a callback based schedule logic to update dynamic capabilities
of store when operator enabled it by a option.

4. Refactoring on existing disablement logic on driver add() interface,
to use consistent capabilities way to handle it, removed add_disabled().

5. Therefor the related exception conversion logic for other interfaces
are redundant, due to now we can raise proper exception directly from
the checker.

6. Added the logic to recreate drive object if the storage and/or driver
isn't stateless.

Few minor changes need to be added to Glance side:
Change Ibbc85b6bc2ea98c564d316db2874d7df5aac32a6 .

docImpact
Implements: blueprint store-capabilities

Change-Id: Iedf0d4f829e46ca64c3f4fc6a7dfee54d9b0605b
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>

1 files changed, 210 insertions, 0 deletions

diff --git a/glance_store/capabilities.py b/glance_store/capabilities.py
new file mode 100644
index 0000000..704ed5d
--- /dev/null
+++ b/glance_store/capabilities.py
@@ -0,0 +1,210 @@
+# Copyright (c) 2015 IBM, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Glance Store capability"""
+
+import logging
+import threading
+import time
+
+from eventlet import tpool
+
+from glance_store import exceptions
+from glance_store import i18n
+
+_LW = i18n._LW
+_STORE_CAPABILITES_UPDATE_SCHEDULING_BOOK = {}
+_STORE_CAPABILITES_UPDATE_SCHEDULING_LOCK = threading.Lock()
+LOG = logging.getLogger(__name__)
+
+# Store capability constants
+NONE = 0b00000000
+ALL = 0b11111111
+READ_ACCESS = 0b00000001
+READ_OFFSET = 0b00000011  # Included READ_ACCESS
+READ_CHUNK = 0b00000101  # Included READ_ACCESS
+READ_RANDOM = 0b00000111  # READ_OFFSET | READ_CHUNK
+WRITE_ACCESS = 0b00001000
+WRITE_OFFSET = 0b00011000  # Included WRITE_ACCESS
+WRITE_CHUNK = 0b00101000  # Included WRITE_ACCESS
+WRITE_RANDOM = 0b00111000  # WRITE_OFFSET | WRITE_CHUNK
+RW_ACCESS = 0b00001001  # READ_ACCESS | WRITE_ACCESS
+RW_OFFSET = 0b00011011  # READ_OFFSET | WRITE_OFFSET
+RW_CHUNK = 0b00101101  # READ_CHUNK | WRITE_CHUNK
+RW_RANDOM = 0b00111111  # RW_OFFSET | RW_CHUNK
+DRIVER_REUSABLE = 0b01000000  # driver is stateless and can be reused safely
+
+
+class StoreCapability(object):
+
+    def __init__(self):
+        # Set static store capabilities base on
+        # current driver implementation.
+        self._capabilities = getattr(self.__class__, "_CAPABILITIES", 0)
+
+    @property
+    def capabilities(self):
+        return self._capabilities
+
+    @staticmethod
+    def contains(x, y):
+        return x & y == y
+
+    def update_capabilities(self):
+        """
+        Update dynamic storage capabilities based on current
+        driver configuration and backend status when needed.
+
+        As a hook, the function will be triggered in two cases:
+        calling once after store driver get configured, it was
+        used to update dynamic storage capabilities based on
+        current driver configuration, or calling when the
+        capabilities checking of an operation failed every time,
+        this was used to refresh dynamic storage capabilities
+        based on backend status then.
+
+        This function shouldn't raise any exception out.
+        """
+        LOG.debug(("Store %s doesn't support updating dynamic "
+                   "storage capabilities. Please overwrite "
+                   "'update_capabilities' method of the store to "
+                   "implement updating logics if needed.") %
+                  self.__class__.__name__)
+
+    def is_capable(self, *capabilities):
+        """
+        Check if requested capability(s) are supported by
+        current driver instance.
+
+        :param capabilities: required capability(s).
+        """
+        caps = 0
+
+        for cap in capabilities:
+            caps |= int(cap)
+
+        return self.contains(self.capabilities, caps)
+
+    def set_capabilities(self, *dynamic_capabilites):
+        """
+        Set dynamic storage capabilities based on current
+        driver configuration and backend status.
+
+        :param dynamic_capabilites: dynamic storage capability(s).
+        """
+        for cap in dynamic_capabilites:
+            self._capabilities |= int(cap)
+
+    def unset_capabilities(self, *dynamic_capabilites):
+        """
+        Unset dynamic storage capabilities.
+
+        :param dynamic_capabilites: dynamic storage capability(s).
+        """
+        caps = 0
+
+        for cap in dynamic_capabilites:
+            caps |= int(cap)
+
+        # TODO(zhiyan): Cascaded capability removal is
+        # skipped currently, we can add it back later
+        # when a concrete requirement comes out.
+        # For example, when removing READ_ACCESS, all
+        # read related capabilities need to be removed
+        # together, e.g. READ_RANDOM.
+
+        self._capabilities &= ~caps
+
+
+def _schedule_capabilities_update(store):
+    def _update_capabilities(store, context):
+        with context['lock']:
+            if context['updating']:
+                return
+            context['updating'] = True
+            try:
+                store.update_capabilities()
+            except Exception:
+                pass
+            finally:
+                context['updating'] = False
+                # NOTE(zhiyan): Update 'latest_update' field
+                # in anyway even an exception raised, to
+                # prevent call problematic routine cyclically.
+                context['latest_update'] = int(time.time())
+
+    global _STORE_CAPABILITES_UPDATE_SCHEDULING_BOOK
+    book = _STORE_CAPABILITES_UPDATE_SCHEDULING_BOOK
+    if store not in book:
+        with _STORE_CAPABILITES_UPDATE_SCHEDULING_LOCK:
+            if store not in book:
+                book[store] = {'latest_update': int(time.time()),
+                               'lock': threading.Lock(),
+                               'updating': False}
+    else:
+        context = book[store]
+        # NOTE(zhiyan): We don't need to lock 'latest_update'
+        # field for check since time increased one-way only.
+        sec = (int(time.time()) - context['latest_update'] -
+               store.conf.glance_store.store_capabilities_update_min_interval)
+        if sec >= 0:
+            if not context['updating']:
+                # NOTE(zhiyan): Using a real thread pool instead
+                # of green pool due to store capabilities updating
+                # probably calls some inevitably blocking code for
+                # IO operation on remote or local storage.
+                # Eventlet allows operator to uses environment var
+                # EVENTLET_THREADPOOL_SIZE to desired pool size.
+                tpool.execute(_update_capabilities, store, context)
+
+
+def check(store_op_fun):
+
+    def op_checker(store, *args, **kwargs):
+        # NOTE(zhiyan): Trigger the hook of updating store
+        # dynamic capabilities based on current store status.
+        if store.conf.glance_store.store_capabilities_update_min_interval > 0:
+            _schedule_capabilities_update(store)
+
+        op_cap_map = {
+            'get': [READ_ACCESS,
+                    READ_OFFSET if kwargs.get('offset') else NONE,
+                    READ_CHUNK if kwargs.get('chunk_size') else NONE],
+            'add': [WRITE_ACCESS],
+            'delete': [WRITE_ACCESS]}
+
+        op_exec_map = {
+            'get': (exceptions.StoreRandomGetNotSupported
+                    if kwargs.get('offset') or kwargs.get('chunk_size') else
+                    exceptions.StoreGetNotSupported),
+            'add': exceptions.StoreAddDisabled,
+            'delete': exceptions.StoreDeleteNotSupported}
+
+        op = store_op_fun.__name__.lower()
+
+        try:
+            req_cap = op_cap_map[op]
+        except KeyError:
+            LOG.warn(_LW('The capability of operation "%s" '
+                         'could not be checked.' % op))
+        else:
+            if not store.is_capable(*req_cap):
+                kwargs.setdefault('offset', 0)
+                kwargs.setdefault('chunk_size', None)
+                raise op_exec_map[op](**kwargs)
+
+        return store_op_fun(store, *args, **kwargs)
+
+    return op_checker