Implement logic in CarStorageMonitoringManager to detect the cost (in terms of disk I/O) of the previous shutdown

ext4 and f2fs offer lifetime_write_kbytes files via sysfs that let userspace discover the amount of data
written to each individual partition throughout its lifetime.

Using this information, we execute this algorithm:
- when CarService goes down, store lifetime_write_kbytes info for all mounted partitions;
- at the next boot, calculate lifetime_write_kbytes for all mounted partitions again;
- for every partition that existed at both shutdown and reboot, calculate the difference of the written amount;
- add up those deltas: this is the total amount of writes since CarService went down;
- take the aggregate UID I/O activity, and add up all bytes written to disk inferred from there: this is the cost of getting where we are;
- subtract this aggregate from the previously computed total delta: this is a fair approximation of the cost of shutdown

Test: tests in carservice_test and carservice_unit_test
Bug: 32512551
Change-Id: Ia791eaa1fdb4bf026c1760e2bd333c30a413721f
Fixes: 72236603

2 files changed, 18 insertions, 0 deletions

diff --git a/tests/common_utils/src/com/android/car/test/utils/TemporaryDirectory.java b/tests/common_utils/src/com/android/car/test/utils/TemporaryDirectory.java
index fa5727d903..e1c4735faa 100644
--- a/tests/common_utils/src/com/android/car/test/utils/TemporaryDirectory.java
+++ b/tests/common_utils/src/com/android/car/test/utils/TemporaryDirectory.java
@@ -60,6 +60,10 @@ public class TemporaryDirectory implements AutoCloseable {
 
     private static final SimpleFileVisitor<Path> DELETE = new DeletingVisitor();
 
+    TemporaryDirectory(Path directory) throws IOException {
+        mDirectory = Files.createDirectory(directory);
+    }
+
     public TemporaryDirectory(@Nullable String prefix) throws IOException {
         if (prefix == null) {
             prefix = TemporaryDirectory.class.getSimpleName();
@@ -77,4 +81,10 @@ public class TemporaryDirectory implements AutoCloseable {
     public File getDirectory() {
         return mDirectory.toFile();
     }
+
+    public Path getPath() { return mDirectory; }
+
+    public TemporaryDirectory getSubdirectory(String name) throws IOException {
+        return new TemporaryDirectory(mDirectory.resolve(name));
+    }
 }
diff --git a/tests/common_utils/src/com/android/car/test/utils/TemporaryFile.java b/tests/common_utils/src/com/android/car/test/utils/TemporaryFile.java
index 518f4a9b4d..cd0f323223 100644
--- a/tests/common_utils/src/com/android/car/test/utils/TemporaryFile.java
+++ b/tests/common_utils/src/com/android/car/test/utils/TemporaryFile.java
@@ -46,6 +46,10 @@ public final class TemporaryFile implements AutoCloseable {
         mFile = File.createTempFile(prefix, String.valueOf(SystemClock.elapsedRealtimeNanos()));
     }
 
+    public TemporaryFile(File path) {
+        mFile = path;
+    }
+
     @Override
     public void close() throws Exception {
         Files.delete(mFile.toPath());
@@ -57,6 +61,10 @@ public final class TemporaryFile implements AutoCloseable {
         writer.close();
     }
 
+    public FileWriter newFileWriter() throws IOException {
+        return new FileWriter(mFile);
+    }
+
     public File getFile() {
         return mFile;
     }