2 files changed, 69 insertions, 0 deletions

diff --git a/bootloader_message/bootloader_message.cpp b/bootloader_message/bootloader_message.cpp
index f838930fd..4f7085db9 100644
--- a/bootloader_message/bootloader_message.cpp
+++ b/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);
diff --git a/bootloader_message/include/bootloader_message/bootloader_message.h b/bootloader_message/include/bootloader_message/bootloader_message.h
index e3425fc8b..3a3b862aa 100644
--- a/bootloader_message/include/bootloader_message/bootloader_message.h
+++ b/bootloader_message/include/bootloader_message/bootloader_message.h
@@ -185,6 +185,28 @@ static_assert(sizeof(struct bootloader_control) ==
               "struct bootloader_control has wrong size");
 #endif
 
+// Holds Virtual A/B merge status information. Current version is 1. New fields
+// must be added to the end.
+struct misc_virtual_ab_message {
+  uint8_t version;
+  uint8_t merge_status;  // IBootControl 1.1, MergeStatus enum.
+  uint8_t source_slot;   // Slot number when merge_status was written.
+  uint8_t reserved[61];
+} __attribute__((packed));
+
+#define MISC_VIRTUAL_AB_MESSAGE_VERSION 1
+
+#if (__STDC_VERSION__ >= 201112L) || defined(__cplusplus)
+static_assert(sizeof(struct misc_virtual_ab_message) == 64,
+              "struct misc_virtual_ab_message has wrong size");
+#endif
+
+// This struct is not meant to be used directly, rather, it is to make
+// computation of offsets easier. New fields must be added to the end.
+struct misc_system_space_layout {
+  misc_virtual_ab_message virtual_ab_message;
+} __attribute__((packed));
+
 #ifdef __cplusplus
 
 #include <string>
@@ -247,6 +269,10 @@ bool ReadMiscPartitionVendorSpace(void* data, size_t size, size_t offset, std::s
 // offset is in relative to the start of the vendor space.
 bool WriteMiscPartitionVendorSpace(const void* data, size_t size, size_t offset, std::string* err);
 
+// Read or write the Virtual A/B message from system space in /misc.
+bool ReadMiscVirtualAbMessage(misc_virtual_ab_message* message, std::string* err);
+bool WriteMiscVirtualAbMessage(const misc_virtual_ab_message& message, std::string* err);
+
 #else
 
 #include <stdbool.h>