[RFC PATCH v5 2/3] softmmu/memory: add memory_region_try_add_subregion function

[Damien Hedde <damien.hedde@greensocs.com>]

It allows adding a subregion to a memory region with error handling.
Like memory_region_add_subregion_overlap(), it handles priority as
well. Apart from 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 of this function in the
context of qapi command which needs error handling support.

Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
---
v5:
 + rebase, new callsite

---
 include/exec/memory.h | 22 ++++++++++++++++++++++
 softmmu/memory.c      | 26 +++++++++++++++++---------
 2 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index f1c19451bc..36f2e86be5 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -2215,6 +2215,28 @@ 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 7ba2048836..5ea4000830 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -2541,27 +2541,34 @@ 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)
 {
     MemoryRegion *alias;
 
-    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;
     for (alias = subregion->alias; alias; alias = alias->alias) {
         alias->mapped_via_alias++;
     }
     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,
@@ -2569,8 +2576,8 @@ 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,
@@ -2626,7 +2633,8 @@ static void memory_region_readd_subregion(MemoryRegion *mr)
         memory_region_transaction_begin();
         memory_region_ref(mr);
         memory_region_del_subregion(container, mr);
-        memory_region_add_subregion_common(container, mr->addr, mr);
+        memory_region_try_add_subregion(container, mr->addr, mr, mr->priority,
+                                        &error_abort);
         memory_region_unref(mr);
         memory_region_transaction_commit();
     }
-- 
2.36.1