[RFC PATCH v2 11/16] softmmu/memory: add memory_region_try_add_subregion function

[Damien Hedde <damien.hedde@xxxxxxxxxxxxx>]

It allows to try to add a subregion to a memory region with error
handling. Like memory_region_add_subregion_overlap, it handles
priority as well.
Apart the error handling, the behavior is the same. It can be used
to do the simple memory_region_add_subregion() (with no overlap) by
setting the priority parameter to 0.

This commit is a preparation to further use this function in the
context of qmp command which needs error handling support.

Signed-off-by: Damien Hedde <damien.hedde@xxxxxxxxxxxxx>
---

Adding a new function is obviously not ideal. But there is ~900
occurrences of memory_region_add_subregion[_overlap] calls in the code
base. We do not really see an alternative here.
---
 include/exec/memory.h | 22 ++++++++++++++++++++++
 softmmu/memory.c      | 22 ++++++++++++++--------
 2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index c3d417d317..422e1eda67 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -2162,6 +2162,28 @@ void memory_region_add_subregion_overlap(MemoryRegion 
*mr,
                                          MemoryRegion *subregion,
                                          int priority);
 
+/**
+ * memory_region_try_add_subregion: Add a subregion to a container
+ *                                  with error handling.
+ *
+ * Behaves like memory_region_add_subregion_overlap(), but errors are
+ * reported if the subregion cannot be added.
+ *
+ * @mr: the region to contain the new subregion; must be a container
+ *      initialized with memory_region_init().
+ * @offset: the offset relative to @mr where @subregion is added.
+ * @subregion: the subregion to be added.
+ * @priority: used for resolving overlaps; highest priority wins.
+ * @errp: pointer to Error*, to store an error if it happens.
+ *
+ * Returns: True in case of success, false otherwise.
+ */
+bool memory_region_try_add_subregion(MemoryRegion *mr,
+                                     hwaddr offset,
+                                     MemoryRegion *subregion,
+                                     int priority,
+                                     Error **errp);
+
 /**
  * memory_region_get_ram_addr: Get the ram address associated with a memory
  *                             region
diff --git a/softmmu/memory.c b/softmmu/memory.c
index bfedaf9c4d..eac61f8236 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -2513,22 +2513,28 @@ done:
     memory_region_transaction_commit();
 }
 
-static void memory_region_add_subregion_common(MemoryRegion *mr,
-                                               hwaddr offset,
-                                               MemoryRegion *subregion)
+bool memory_region_try_add_subregion(MemoryRegion *mr,
+                                     hwaddr offset,
+                                     MemoryRegion *subregion,
+                                     int priority,
+                                     Error **errp)
 {
-    assert(!subregion->container);
+    if (subregion->container) {
+        error_setg(errp, "The memory region is already in another region");
+        return false;
+    }
+    subregion->priority = priority;
     subregion->container = mr;
     subregion->addr = offset;
     memory_region_update_container_subregions(subregion);
+    return true;
 }
 
 void memory_region_add_subregion(MemoryRegion *mr,
                                  hwaddr offset,
                                  MemoryRegion *subregion)
 {
-    subregion->priority = 0;
-    memory_region_add_subregion_common(mr, offset, subregion);
+    memory_region_try_add_subregion(mr, offset, subregion, 0, &error_abort);
 }
 
 void memory_region_add_subregion_overlap(MemoryRegion *mr,
@@ -2536,8 +2542,8 @@ void memory_region_add_subregion_overlap(MemoryRegion *mr,
                                          MemoryRegion *subregion,
                                          int priority)
 {
-    subregion->priority = priority;
-    memory_region_add_subregion_common(mr, offset, subregion);
+    memory_region_try_add_subregion(mr, offset, subregion, priority,
+                                    &error_abort);
 }
 
 void memory_region_del_subregion(MemoryRegion *mr,
-- 
2.33.0