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+Introduction:
+
+This document describes lock order dependencies in Ganeti.
+It is divided by functional sections
+
+
+Opcode Execution Locking:
+
+These locks are declared by Logical Units (LUs) (in cmdlib.py) and acquired by
+the Processor (in mcpu.py) with the aid of the Ganeti Locking Library
+(locking.py). They are acquired in the following order:
+
+ * BGL: this is the Big Ganeti Lock, it exists for retrocompatibility. New LUs
+ acquire it in a shared fashion, and are able to execute all toghether
+ (baring other lock waits) while old LUs acquire it exclusively and can only
+ execute one at a time, and not at the same time with new LUs.
+ * Instance locks: can be declared in ExpandNames() o DeclareLocks() by an LU,
+ and have the same name as the instance itself. They are acquired as a set.
+ Internally the locking library acquired them in alphabetical order.
+ * Node locks: can be declared in ExpandNames() o DeclareLocks() by an LU, and
+ have the same name as the node itself. They are acquired as a set.
+ Internally the locking library acquired them in alphabetical order. Given
+ this order it's possible to safely acquire a set of instances, and then the
+ nodes they reside on.
+
+The ConfigWriter (in config.py) is also protected by a SharedLock, which is
+shared by functions that read the config and acquired exclusively by functions
+that modify it. Since the ConfigWriter calls rpc.call_upload_file to all nodes
+to distribute the config without holding the node locks, this call must be able
+to execute on the nodes in parallel with other operations (but not necessarily
+concurrently with itself on the same file, as inside the ConfigWriter this is
+called with the internal config lock held.
+