Add support for compressed snapshot merges in fastboot.

SnapshotManager::New() is now preferred in recovery. Previously we used
NewForFirstStageMount(), which is technically incorrect as that enables
code paths specifically for first-stage init.

We also explicitly label the snapuserd context, since rootfs in recovery
has unlabelled files.

Finally, we add a timeout to internal calls to
CreateSnapshotsAndLogicalPartitions. Without this, WaitForDevice() calls
will terminate immediately, which breaks VABC given the more complex
device stacking that is created.

Bug: 168258606
Test: fastboot snapshot-update merge
Change-Id: I3a663b95c0b1eabaf14e6fde409c6902653c3c5e
diff --git a/fastboot/device/commands.cpp b/fastboot/device/commands.cpp
index 2b2a0bf..b2b6a9e 100644
--- a/fastboot/device/commands.cpp
+++ b/fastboot/device/commands.cpp
@@ -659,7 +659,7 @@
             return device->WriteFail("No snapshot merge is in progress");
         }
 
-        auto sm = SnapshotManager::NewForFirstStageMount();
+        auto sm = SnapshotManager::New();
         if (!sm) {
             return device->WriteFail("Unable to create SnapshotManager");
         }
diff --git a/fs_mgr/libsnapshot/snapshot.cpp b/fs_mgr/libsnapshot/snapshot.cpp
index 9329725..a171c23 100644
--- a/fs_mgr/libsnapshot/snapshot.cpp
+++ b/fs_mgr/libsnapshot/snapshot.cpp
@@ -94,7 +94,11 @@
     if (!info) {
         info = new DeviceInfo();
     }
-    return std::unique_ptr<SnapshotManager>(new SnapshotManager(info));
+    auto sm = std::unique_ptr<SnapshotManager>(new SnapshotManager(info));
+    if (info->IsRecovery()) {
+        sm->ForceLocalImageManager();
+    }
+    return sm;
 }
 
 std::unique_ptr<SnapshotManager> SnapshotManager::NewForFirstStageMount(IDeviceInfo* info) {
@@ -3169,7 +3173,7 @@
 
     auto slot_number = SlotNumberForSlotSuffix(device_->GetSlotSuffix());
     auto super_path = device_->GetSuperDevice(slot_number);
-    if (!CreateLogicalAndSnapshotPartitions(super_path)) {
+    if (!CreateLogicalAndSnapshotPartitions(super_path, 20s)) {
         LOG(ERROR) << "Unable to map partitions to complete merge.";
         return false;
     }
@@ -3209,7 +3213,7 @@
 
     auto slot_number = SlotNumberForSlotSuffix(device_->GetSlotSuffix());
     auto super_path = device_->GetSuperDevice(slot_number);
-    if (!CreateLogicalAndSnapshotPartitions(super_path)) {
+    if (!CreateLogicalAndSnapshotPartitions(super_path, 20s)) {
         LOG(ERROR) << "Unable to map partitions to complete merge.";
         return false;
     }
@@ -3355,7 +3359,7 @@
     auto slot_suffix = device_->GetOtherSlotSuffix();
     auto slot_number = SlotNumberForSlotSuffix(slot_suffix);
     auto super_path = device_->GetSuperDevice(slot_number);
-    if (!CreateLogicalAndSnapshotPartitions(super_path)) {
+    if (!CreateLogicalAndSnapshotPartitions(super_path, 20s)) {
         LOG(ERROR) << "Unable to map partitions.";
         return CreateResult::ERROR;
     }
diff --git a/fs_mgr/libsnapshot/snapuserd.rc b/fs_mgr/libsnapshot/snapuserd.rc
index f2d21ac..4bf34a2 100644
--- a/fs_mgr/libsnapshot/snapuserd.rc
+++ b/fs_mgr/libsnapshot/snapuserd.rc
@@ -4,3 +4,4 @@
     disabled
     user root
     group root system
+    seclabel u:r:snapuserd:s0