From 9b4f3eaf17e3200fe77a7b094abb6a7a5f7a854f Mon Sep 17 00:00:00 2001
From: Yi-Yo Chiang <yochiang@google.com>
Date: Sun, 20 Mar 2022 16:49:32 +0800
Subject: [PATCH] dynsystem.SparseInputStream: Implement read(buf, off, len)

InstallationAsyncTask calls SparseInputStream.read(buf, off, len),
however SparseInputStream didn't override that method, so the method
actually fallbacks to the default implementation, which is a for-loop
calling read() (single byte). This is a significant performance hit.

This modest fix boosts the DSU installation time significantly:
* physical device: 45s -> 15s
* virtual device: 30s -> 7s

Bug: 225310919
Test: start a Dynamic System installation
Change-Id: I5a61dc2e9554719aece43491b813f6647b4bcc65
---
 .../android/dynsystem/SparseInputStream.java  | 20 ++++++++-----------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/packages/DynamicSystemInstallationService/src/com/android/dynsystem/SparseInputStream.java b/packages/DynamicSystemInstallationService/src/com/android/dynsystem/SparseInputStream.java
index 4117d0f07e0f4..7d2326693a174 100644
--- a/packages/DynamicSystemInstallationService/src/com/android/dynsystem/SparseInputStream.java
+++ b/packages/DynamicSystemInstallationService/src/com/android/dynsystem/SparseInputStream.java
@@ -133,36 +133,32 @@ public class SparseInputStream extends InputStream {
         return mLeft == 0;
     }
 
-    /**
-     * It overrides the InputStream.read(byte[] buf)
-     */
-    public int read(byte[] buf) throws IOException {
+    @Override
+    public int read(byte[] buf, int off, int len) throws IOException {
         if (!mIsSparse) {
-            return mIn.read(buf);
+            return mIn.read(buf, off, len);
         }
         if (prepareChunk()) return -1;
         int n = -1;
         switch (mCur.mChunkType) {
             case SparseChunk.RAW:
-                n = mIn.read(buf, 0, (int) min(mLeft, buf.length));
+                n = mIn.read(buf, off, (int) min(mLeft, len));
                 mLeft -= n;
                 return n;
             case SparseChunk.DONTCARE:
-                n = (int) min(mLeft, buf.length);
-                Arrays.fill(buf, 0, n - 1, (byte) 0);
+                n = (int) min(mLeft, len);
+                Arrays.fill(buf, off, off + n, (byte) 0);
                 mLeft -= n;
                 return n;
             case SparseChunk.FILL:
                 // The FILL type is rarely used, so use a simple implmentation.
-                return super.read(buf);
+                return super.read(buf, off, len);
             default:
                 throw new IOException("Unsupported Chunk:" + mCur.toString());
         }
     }
 
-    /**
-     * It overrides the InputStream.read()
-     */
+    @Override
     public int read() throws IOException {
         if (!mIsSparse) {
             return mIn.read();