From 56abaa0959e8cf691d176517b1cea276da01a638 Mon Sep 17 00:00:00 2001
From: Frederick Mayle <fmayle@google.com>
Date: Tue, 13 Dec 2022 15:40:57 -0800
Subject: [PATCH] debuggerd: simplify output handling

Just noticed some opportunities while skimming.

Test: adb shell debuggerd $(adb shell pidof com.android.systemui)
Test: All unit tests pass (both 32 bit and 64 bit).
Test: Ran unit tests in a loop hundreds of times.
Change-Id: I428d0cf599ed603a21944b084b95594db893cbd5
---
 debuggerd/client/debuggerd_client.cpp |  7 +++++++
 debuggerd/debuggerd.cpp               | 28 ++++-----------------------
 2 files changed, 11 insertions(+), 24 deletions(-)

diff --git a/debuggerd/client/debuggerd_client.cpp b/debuggerd/client/debuggerd_client.cpp
index c9e097ea3..bd1e91d34 100644
--- a/debuggerd/client/debuggerd_client.cpp
+++ b/debuggerd/client/debuggerd_client.cpp
@@ -276,6 +276,13 @@ bool debuggerd_trigger_dump(pid_t tid, DebuggerdDumpType dump_type, unsigned int
       return false;
     }
 
+    // WARNING: It's not possible to replace the below with a splice call.
+    // Due to the way debuggerd does many small writes across the pipe,
+    // this would cause splice to copy a page for each write. The second
+    // pipe fills up based on the number of pages being copied, even
+    // though there is not much data being transferred per page. When
+    // the second pipe is full, everything stops since there is nothing
+    // reading the second pipe to clear it.
     char buf[1024];
     rc = TEMP_FAILURE_RETRY(read(pipe_read.get(), buf, sizeof(buf)));
     if (rc == 0) {
diff --git a/debuggerd/debuggerd.cpp b/debuggerd/debuggerd.cpp
index e20e8d9e1..26726cf89 100644
--- a/debuggerd/debuggerd.cpp
+++ b/debuggerd/debuggerd.cpp
@@ -41,22 +41,6 @@ static void usage(int exit_code) {
   _exit(exit_code);
 }
 
-static std::thread spawn_redirect_thread(unique_fd fd) {
-  return std::thread([fd{ std::move(fd) }]() {
-    while (true) {
-      char buf[BUFSIZ];
-      ssize_t rc = TEMP_FAILURE_RETRY(read(fd.get(), buf, sizeof(buf)));
-      if (rc <= 0) {
-        return;
-      }
-
-      if (!android::base::WriteFully(STDOUT_FILENO, buf, rc)) {
-        return;
-      }
-    }
-  });
-}
-
 int main(int argc, char* argv[]) {
   if (argc <= 1) usage(0);
   if (argc > 3) usage(1);
@@ -107,14 +91,11 @@ int main(int argc, char* argv[]) {
     }
   }
 
-  unique_fd piperead, pipewrite;
-  if (!Pipe(&piperead, &pipewrite)) {
-    err(1, "failed to create pipe");
+  unique_fd output_fd(fcntl(STDOUT_FILENO, F_DUPFD_CLOEXEC, 0));
+  if (output_fd.get() == -1) {
+    err(1, "failed to fcntl dup stdout");
   }
-
-  std::thread redirect_thread = spawn_redirect_thread(std::move(piperead));
-  if (!debuggerd_trigger_dump(proc_info.pid, dump_type, 0, std::move(pipewrite))) {
-    redirect_thread.join();
+  if (!debuggerd_trigger_dump(proc_info.pid, dump_type, 0, std::move(output_fd))) {
     if (pid == proc_info.pid) {
       errx(1, "failed to dump process %d", pid);
     } else {
@@ -122,6 +103,5 @@ int main(int argc, char* argv[]) {
     }
   }
 
-  redirect_thread.join();
   return 0;
 }