fastboot: Implement helper commands for Virtual A/B.

This introduces two new commands to the fastboot protocol:

  - getvar snapshot-update-status - Return "none", "snapshotted", or
    "merging" depending on the current status set by the boot control
    HAL.
  - snapshot-update [cancel] - Cancel any pending snapshot-based updates
    via the boot control HAL. After this, the HAL should return
    MergeStatus::CANCELLED and "update-merge-status" should be "none".
    If no argument is specified, the snapshot-update-status is returned
    via an INFO response.

Bootloaders are expected to implement this in a manner consistent with
the boot control HAL.

Fastboot-based tooling should expect wipes of userdata to fail when
update-merge-status returns "merging". Thus, the force flag now cancel
any pending snapshots.

Bug: 139154945
Test: fastboot getvar snapshot-update-status
      fastboot snapshot-update cancel
      fastboot snapshot-update

Change-Id: Idc423fe7656b212e929e64eb0e6b85b453e0e8dc

1 files changed, 25 insertions, 0 deletions

diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index 2fe3b1a9e..7ce7c7c0e 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -396,6 +396,9 @@ static int show_help() {
             " gsi wipe|disable           Wipe or disable a GSI installation (fastbootd only).\n"
             " wipe-super [SUPER_EMPTY]   Wipe the super partition. This will reset it to\n"
             "                            contain an empty set of default dynamic partitions.\n"
+            " snapshot-update cancel     On devices that support snapshot-based updates, cancel\n"
+            "                            an in-progress update. This may make the device\n"
+            "                            unbootable until it is reflashed.\n"
             "\n"
             "boot image:\n"
             " boot KERNEL [RAMDISK [SECOND]]\n"
@@ -1216,6 +1219,14 @@ static void reboot_to_userspace_fastboot() {
     target_sparse_limit = -1;
 }
 
+static void CancelSnapshotIfNeeded() {
+    std::string merge_status = "none";
+    if (fb->GetVar(FB_VAR_SNAPSHOT_UPDATE_STATUS, &merge_status) == fastboot::SUCCESS &&
+        merge_status != "none") {
+        fb->SnapshotUpdateCommand("Cancel");
+    }
+}
+
 class ImageSource {
   public:
     virtual bool ReadFile(const std::string& name, std::vector<char>* out) const = 0;
@@ -1268,6 +1279,8 @@ void FlashAllTool::Flash() {
     DetermineSecondarySlot();
     CollectImages();
 
+    CancelSnapshotIfNeeded();
+
     // First flash boot partitions. We allow this to happen either in userspace
     // or in bootloader fastboot.
     FlashImages(boot_images_);
@@ -2071,12 +2084,24 @@ int FastBootTool::Main(int argc, char* argv[]) {
                 image = next_arg(&args);
             }
             do_wipe_super(image, slot_override);
+        } else if (command == "snapshot-update") {
+            std::string arg;
+            if (!args.empty()) {
+                arg = next_arg(&args);
+            }
+            if (!arg.empty() && arg != "cancel") {
+                syntax_error("expected: snapshot-update [cancel]");
+            }
+            fb->SnapshotUpdateCommand(arg);
         } else {
             syntax_error("unknown command %s", command.c_str());
         }
     }
 
     if (wants_wipe) {
+        if (force_flash) {
+            CancelSnapshotIfNeeded();
+        }
         std::vector<std::string> partitions = { "userdata", "cache", "metadata" };
         for (const auto& partition : partitions) {
             std::string partition_type;