init: Pass a uevent regen callback to libsnapshot.

In first-stage init, libsnapshot needs to know how to wait for device
paths, since ueventd isn't running yet. We do this by passing a callback
wrapping BlockDevInitializer.

Bug: 173476209
Test: device boots into first-stage init after full VABC ota
Change-Id: I9a87f98824e65a9379cb0b99c001e28cccd9d205

init/block_dev_initializer.cpp

@@ -40,8 +40,8 @@ bool BlockDevInitializer::InitDeviceMapper() {
     return InitMiscDevice("device-mapper");
 }
 
-bool BlockDevInitializer::InitDmUser() {
-    return InitMiscDevice("dm-user");
+bool BlockDevInitializer::InitDmUser(const std::string& name) {
+    return InitMiscDevice("dm-user!" + name);
 }
 
 bool BlockDevInitializer::InitMiscDevice(const std::string& name) {

init/block_dev_initializer.h

@@ -27,7 +27,7 @@ class BlockDevInitializer final {
     BlockDevInitializer();
 
     bool InitDeviceMapper();
-    bool InitDmUser();
+    bool InitDmUser(const std::string& name);
     bool InitDevices(std::set<std::string> devices);
     bool InitDmDevice(const std::string& device);
 

init/first_stage_mount.cpp

@@ -343,6 +343,15 @@ bool FirstStageMount::CreateLogicalPartitions() {
             if (!InitRequiredDevices({"userdata"})) {
                 return false;
             }
+            sm->SetUeventRegenCallback([this](const std::string& device) -> bool {
+                if (android::base::StartsWith(device, "/dev/block/dm-")) {
+                    return block_dev_init_.InitDmDevice(device);
+                }
+                if (android::base::StartsWith(device, "/dev/dm-user/")) {
+                    return block_dev_init_.InitDmUser(android::base::Basename(device));
+                }
+                return block_dev_init_.InitDevices({device});
+            });
             return sm->CreateLogicalAndSnapshotPartitions(super_path_);
         }
     }