bootloader_message: Add helpers for handling IBootControl MergeStatus.

Move merge_status from bootloader_control_ab, which is in vendor space,
to a new generic AOSP struct in system space. This will allow more
devices to share the same HAL implementation.

This patch also changes libboot_control to compensate for merge_status
moving out of vendor space. The reference HAL library now also provides
separate helper functions for managing the merge status, so devices
using a custom boot control HAL can still take advantage of the new misc
implementation.

Bug: 139156011
Test: manual test
Change-Id: I5cd824e25f9d07aad1476301def5cdc3f506b029

bootloader_message/bootloader_message.cpp

@@ -292,6 +292,49 @@ bool WriteMiscPartitionVendorSpace(const void* data, size_t size, size_t offset,
                               err);
 }
 
+static bool ValidateSystemSpaceRegion(size_t offset, size_t size, std::string* err) {
+  if (size <= SYSTEM_SPACE_SIZE_IN_MISC && offset <= (SYSTEM_SPACE_SIZE_IN_MISC - size)) {
+    return true;
+  }
+  *err = android::base::StringPrintf("Out of bound access (offset %zu size %zu)", offset, size);
+  return false;
+}
+
+static bool ReadMiscPartitionSystemSpace(void* data, size_t size, size_t offset, std::string* err) {
+  if (!ValidateSystemSpaceRegion(offset, size, err)) {
+    return false;
+  }
+  auto misc_blk_device = get_misc_blk_device(err);
+  if (misc_blk_device.empty()) {
+    return false;
+  }
+  return read_misc_partition(data, size, misc_blk_device, SYSTEM_SPACE_OFFSET_IN_MISC + offset,
+                             err);
+}
+
+static bool WriteMiscPartitionSystemSpace(const void* data, size_t size, size_t offset,
+                                          std::string* err) {
+  if (!ValidateSystemSpaceRegion(offset, size, err)) {
+    return false;
+  }
+  auto misc_blk_device = get_misc_blk_device(err);
+  if (misc_blk_device.empty()) {
+    return false;
+  }
+  return write_misc_partition(data, size, misc_blk_device, SYSTEM_SPACE_OFFSET_IN_MISC + offset,
+                              err);
+}
+
+bool ReadMiscVirtualAbMessage(misc_virtual_ab_message* message, std::string* err) {
+  return ReadMiscPartitionSystemSpace(message, sizeof(*message),
+                                      offsetof(misc_system_space_layout, virtual_ab_message), err);
+}
+
+bool WriteMiscVirtualAbMessage(const misc_virtual_ab_message& message, std::string* err) {
+  return WriteMiscPartitionSystemSpace(&message, sizeof(message),
+                                       offsetof(misc_system_space_layout, virtual_ab_message), err);
+}
+
 extern "C" bool write_reboot_bootloader(void) {
   std::string err;
   return write_reboot_bootloader(&err);