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
diff --git a/fastboot/device/commands.cpp b/fastboot/device/commands.cpp
index 4c77c75..dfd5690 100644
--- a/fastboot/device/commands.cpp
+++ b/fastboot/device/commands.cpp
@@ -25,6 +25,7 @@
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
 #include <android-base/unique_fd.h>
+#include <android/hardware/boot/1.1/IBootControl.h>
 #include <cutils/android_reboot.h>
 #include <ext4_utils/wipe.h>
 #include <fs_mgr.h>
@@ -44,8 +45,10 @@
 using ::android::hardware::boot::V1_0::BoolResult;
 using ::android::hardware::boot::V1_0::CommandResult;
 using ::android::hardware::boot::V1_0::Slot;
+using ::android::hardware::boot::V1_1::MergeStatus;
 using ::android::hardware::fastboot::V1_0::Result;
 using ::android::hardware::fastboot::V1_0::Status;
+using IBootControl1_1 = ::android::hardware::boot::V1_1::IBootControl;
 
 struct VariableHandlers {
     // Callback to retrieve the value of a single variable.
@@ -101,7 +104,8 @@
             {FB_VAR_BATTERY_VOLTAGE, {GetBatteryVoltage, nullptr}},
             {FB_VAR_BATTERY_SOC_OK, {GetBatterySoCOk, nullptr}},
             {FB_VAR_HW_REVISION, {GetHardwareRevision, nullptr}},
-            {FB_VAR_SUPER_PARTITION_NAME, {GetSuperPartitionName, nullptr}}};
+            {FB_VAR_SUPER_PARTITION_NAME, {GetSuperPartitionName, nullptr}},
+            {FB_VAR_SNAPSHOT_UPDATE_STATUS, {GetSnapshotUpdateStatus, nullptr}}};
 
     if (args.size() < 2) {
         return device->WriteFail("Missing argument");
@@ -547,3 +551,40 @@
     }
     return device->WriteStatus(FastbootResult::OKAY, "Success");
 }
+
+bool SnapshotUpdateHandler(FastbootDevice* device, const std::vector<std::string>& args) {
+    // Note that we use the HAL rather than mounting /metadata, since we want
+    // our results to match the bootloader.
+    auto hal = device->boot_control_hal();
+    if (!hal) return device->WriteFail("Not supported");
+
+    android::sp<IBootControl1_1> hal11 = IBootControl1_1::castFrom(hal);
+    if (!hal11) return device->WriteFail("Not supported");
+
+    // If no arguments, return the same thing as a getvar. Note that we get the
+    // HAL first so we can return "not supported" before we return the less
+    // specific error message below.
+    if (args.size() < 2 || args[1].empty()) {
+        std::string message;
+        if (!GetSnapshotUpdateStatus(device, {}, &message)) {
+            return device->WriteFail("Could not determine update status");
+        }
+        device->WriteInfo(message);
+        return device->WriteOkay("");
+    }
+
+    if (args.size() != 2 || args[1] != "cancel") {
+        return device->WriteFail("Invalid arguments");
+    }
+
+    MergeStatus status = hal11->getSnapshotMergeStatus();
+    switch (status) {
+        case MergeStatus::SNAPSHOTTED:
+        case MergeStatus::MERGING:
+            hal11->setSnapshotMergeStatus(MergeStatus::CANCELLED);
+            break;
+        default:
+            break;
+    }
+    return device->WriteStatus(FastbootResult::OKAY, "Success");
+}