[PATCH v5 1/2] memory: Update inline documentation

[Akihiko Odaki]

Do not refer to "memory region's reference count"
-------------------------------------------------

Now MemoryRegions do have their own reference counts, but they will not
be used when their owners are not themselves. However, the documentation
of memory_region_ref() says it adds "1 to a memory region's reference
count", which is confusing. Avoid referring to "memory region's
reference count" and just say: "Add a reference to a memory region".
Make a similar change to memory_region_unref() too.

Refer to docs/devel/memory.rst for "owner"
------------------------------------------

memory_region_ref() and memory_region_unref() used to have their own
descriptions of "owner", but they are somewhat out-of-date and
misleading.

In particular, they say "whenever memory regions are accessed outside
the BQL, they need to be preserved against hot-unplug", but protecting
against hot-unplug is not mandatory if it is known that they will never
be hot-unplugged. They also say "MemoryRegions actually do not have
their own reference count", but they actually do. They just will not be
used unless their owners are not themselves.

Refer to docs/devel/memory.rst as the single source of truth instead of
maintaining duplicate descriptions of "owner".

Clarify that owner may be missing

---------------------------------
A memory region may not have an owner, and memory_region_ref() and
memory_region_unref() do nothing for such.

memory: Clarify owner must not call memory_region_ref()
--------------------------------------------------------

The owner must not call this function as it results in a circular
reference.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
 include/exec/memory.h | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 9458e2801d50..cd91fe0c51cf 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -1220,29 +1220,21 @@ void memory_region_init(MemoryRegion *mr,
                         uint64_t size);
 
 /**
- * memory_region_ref: Add 1 to a memory region's reference count
+ * memory_region_ref: Add a reference to a memory region
  *
- * Whenever memory regions are accessed outside the BQL, they need to be
- * preserved against hot-unplug.  MemoryRegions actually do not have their
- * own reference count; they piggyback on a QOM object, their "owner".
- * This function adds a reference to the owner.
- *
- * All MemoryRegions must have an owner if they can disappear, even if the
- * device they belong to operates exclusively under the BQL.  This is because
- * the region could be returned at any time by memory_region_find, and this
- * is usually under guest control.
+ * This function adds a reference to the owner if present.
+ * The owner must not call this function as it results in a circular reference.
+ * See docs/devel/memory.rst to know about owner.
  *
  * @mr: the #MemoryRegion
  */
 void memory_region_ref(MemoryRegion *mr);
 
 /**
- * memory_region_unref: Remove 1 to a memory region's reference count
+ * memory_region_unref: Remove a reference to a memory region
  *
- * Whenever memory regions are accessed outside the BQL, they need to be
- * preserved against hot-unplug.  MemoryRegions actually do not have their
- * own reference count; they piggyback on a QOM object, their "owner".
- * This function removes a reference to the owner and possibly destroys it.
+ * This function removes a reference to the owner and possibly destroys it if
+ * present. See docs/devel/memory.rst to know about owner.
  *
  * @mr: the #MemoryRegion
  */

-- 
2.47.1