[PATCH v2] CODING_STYLE.rst: flesh out our naming conventions.

[Alex Bennée]

Mention a few of the more common naming conventions we follow in the
code base including common variable names and function prefix and
suffix examples.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---
v2
  - punctuation fixes suggested by Cornelia
  - re-worded section on qemu_ prefix
  - expanded on _locked suffix
---
 CODING_STYLE.rst | 30 ++++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/CODING_STYLE.rst b/CODING_STYLE.rst
index 427699e0e42..e7ae44aed7f 100644
--- a/CODING_STYLE.rst
+++ b/CODING_STYLE.rst
@@ -109,8 +109,34 @@ names are lower_case_with_underscores_ending_with_a_t, 
like the POSIX
 uint64_t and family.  Note that this last convention contradicts POSIX
 and is therefore likely to be changed.
 
-When wrapping standard library functions, use the prefix ``qemu_`` to alert
-readers that they are seeing a wrapped version; otherwise avoid this prefix.
+Variable Naming Conventions
+---------------------------
+
+A number of short naming conventions exist for variables that use
+common QEMU types. For example, the architecture independent CPUState
+this is often held as a ``cs`` pointer variable, whereas the concrete
+CPUArchState us usually held in a pointer called ``env``.
+
+Likewise, in device emulation code the common DeviceState is usually
+called ``dev`` with the actual status structure often uses the terse
+``s`` or maybe ``foodev``.
+
+Function Naming Conventions
+---------------------------
+
+The ``qemu_`` prefix is used for utility functions that are widely
+called from across the code-base. This includes wrapped versions of
+standard library functions (e.g. qemu_strtol) where the prefix is
+added to the function name to alert readers that they are seeing a
+wrapped version; otherwise avoid this prefix.
+
+If there are two versions of a function to be called with or without a
+lock held, the function that expects the lock to be already held
+usually uses the suffix ``_locked``.
+
+Public functions (i.e. declared in public headers) tend to be prefixed
+with the subsystem or file they came from. For example, ``tlb_`` for
+functions from ``cputlb.c`` or ``cpu_`` for functions from cpus.c.
 
 Block structure
 ===============
-- 
2.20.1