Wait for dm device to be ready before format

It can sometimes take a moment for the dm-device to appear after
creation, causing operations on it such as formatting to fail.
Ensure the device exists before create_crypto_blk_dev returns.

Test: adb sm set-virtual-disk true and format as adoptable.
Bug: 117586466
Change-Id: Id8f571b551f50fc759e78d917e4ac3080e926722
diff --git a/Utils.cpp b/Utils.cpp
index d348f71..8af616d 100644
--- a/Utils.cpp
+++ b/Utils.cpp
@@ -19,6 +19,7 @@
 #include "Process.h"
 #include "sehandle.h"
 
+#include <android-base/chrono_utils.h>
 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/properties.h>
@@ -41,13 +42,16 @@
 #include <sys/sysmacros.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+
 #include <list>
 #include <mutex>
+#include <thread>
 
 #ifndef UMOUNT_NOFOLLOW
 #define UMOUNT_NOFOLLOW 0x00000008 /* Don't follow symlink on umount */
 #endif
 
+using namespace std::chrono_literals;
 using android::base::ReadFileToString;
 using android::base::StringPrintf;
 
@@ -858,5 +862,20 @@
     return OK;
 }
 
+// TODO(118708649): fix duplication with init/util.h
+status_t WaitForFile(const char* filename, std::chrono::nanoseconds timeout) {
+    android::base::Timer t;
+    while (t.duration() < timeout) {
+        struct stat sb;
+        if (stat(filename, &sb) != -1) {
+            LOG(INFO) << "wait for '" << filename << "' took " << t;
+            return 0;
+        }
+        std::this_thread::sleep_for(10ms);
+    }
+    LOG(WARNING) << "wait for '" << filename << "' timed out and took " << t;
+    return -1;
+}
+
 }  // namespace vold
 }  // namespace android