docs/devel: more documentation on the use of suffixes

Using _qemu is a little confusing. Let's use _compat for these sorts
of things. We should also mention _impl which is another common suffix
in the code base.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20220105135009.1584676-25-alex.bennee@linaro.org>

docs/devel/style.rst

@@ -151,6 +151,12 @@ 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``.
 
+If a function is a shim designed to deal with compatibility
+workarounds we use the suffix ``_compat``. These are generally not
+called directly and aliased to the plain function name via the
+pre-processor. Another common suffix is ``_impl``; it is used for the
+concrete implementation of a function that will not be called
+directly, but rather through a macro or an inline function.
 
 Block structure
 ===============

include/glib-compat.h

@@ -46,9 +46,9 @@
  *    int g_foo(const char *wibble)
  *
  * We must define a static inline function with the same signature that does
- * what we need, but with a "_qemu" suffix e.g.
+ * what we need, but with a "_compat" suffix e.g.
  *
- * static inline void g_foo_qemu(const char *wibble)
+ * static inline void g_foo_compat(const char *wibble)
  * {
  *     #if GLIB_CHECK_VERSION(X, Y, 0)
  *        g_foo(wibble)
@@ -61,7 +61,7 @@
  * ensuring this wrapper function impl doesn't trigger the compiler warning
  * about using too new glib APIs. Finally we can do
  *
- *   #define g_foo(a) g_foo_qemu(a)
+ *   #define g_foo(a) g_foo_compat(a)
  *
  * So now the code elsewhere in QEMU, which *does* have the
  * -Wdeprecated-declarations warning active, can call g_foo(...) as normal,