snapuserd: Factor setpriority/settid calls into a helper.

This allows disabling the code in host builds, since settid() isn't
available in the glibc prebuilt.

Bug: 288273605
Test: snapuserd_test
Change-Id: Ifddb5cb8b04484a1ab0a29794d65c9839759a919

fs_mgr/libsnapshot/snapuserd/Android.bp

@@ -72,6 +72,7 @@ cc_library_static {
         "user-space-merge/snapuserd_transitions.cpp",
         "user-space-merge/snapuserd_verify.cpp",
         "user-space-merge/worker.cpp",
+        "utility.cpp",
     ],
     static_libs: [
         "libbase",

fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp

@@ -16,6 +16,7 @@
 #include "merge_worker.h"
 
 #include "snapuserd_core.h"
+#include "utility.h"
 
 namespace android {
 namespace snapshot {
@@ -550,8 +551,8 @@ bool MergeWorker::Run() {
         return true;
     }
 
-    if (setpriority(PRIO_PROCESS, gettid(), kNiceValueForMergeThreads)) {
-        SNAP_PLOG(ERROR) << "Failed to set priority for TID: " << gettid();
+    if (!SetThreadPriority(kNiceValueForMergeThreads)) {
+        SNAP_PLOG(ERROR) << "Failed to set thread priority";
     }
 
     SNAP_LOG(INFO) << "Merge starting..";

fs_mgr/libsnapshot/snapuserd/user-space-merge/read_worker.cpp

@@ -17,6 +17,7 @@
 #include "read_worker.h"
 
 #include "snapuserd_core.h"
+#include "utility.h"
 
 namespace android {
 namespace snapshot {
@@ -208,8 +209,8 @@ bool ReadWorker::Init() {
 bool ReadWorker::Run() {
     SNAP_LOG(INFO) << "Processing snapshot I/O requests....";
 
-    if (setpriority(PRIO_PROCESS, gettid(), kNiceValueForMergeThreads)) {
-        SNAP_PLOG(ERROR) << "Failed to set priority for TID: " << gettid();
+    if (!SetThreadPriority(kNiceValueForMergeThreads)) {
+        SNAP_PLOG(ERROR) << "Failed to set thread priority";
     }
 
     // Start serving IO

fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp

@@ -17,6 +17,7 @@
 #include "snapuserd_readahead.h"
 
 #include "snapuserd_core.h"
+#include "utility.h"
 
 namespace android {
 namespace snapshot {
@@ -765,8 +766,8 @@ bool ReadAhead::RunThread() {
 
     InitializeIouring();
 
-    if (setpriority(PRIO_PROCESS, gettid(), kNiceValueForMergeThreads)) {
-        SNAP_PLOG(ERROR) << "Failed to set priority for TID: " << gettid();
+    if (!SetThreadPriority(kNiceValueForMergeThreads)) {
+        SNAP_PLOG(ERROR) << "Failed to set thread priority";
     }
 
     while (!RAIterDone()) {

fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_test.cpp

@@ -43,6 +43,7 @@
 #include "snapuserd_core.h"
 #include "testing/dm_user_harness.h"
 #include "testing/temp_device.h"
+#include "utility.h"
 
 DEFINE_string(force_config, "", "Force testing mode with iouring disabled");
 

fs_mgr/libsnapshot/snapuserd/utility.cpp

@@ -0,0 +1,36 @@
+// Copyright (C) 2023 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "utility.h"
+
+#include <sys/resource.h>
+#include <unistd.h>
+
+#include <android-base/file.h>
+
+namespace android {
+namespace snapshot {
+
+using android::base::unique_fd;
+
+bool SetThreadPriority([[maybe_unused]] int priority) {
+#ifdef __ANDROID__
+    return setpriority(PRIO_PROCESS, gettid(), priority) != -1;
+#else
+    return true;
+#endif
+}
+
+}  // namespace snapshot
+}  // namespace android

fs_mgr/libsnapshot/snapuserd/utility.h

@@ -0,0 +1,23 @@
+// Copyright (C) 2023 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+namespace android {
+namespace snapshot {
+
+bool SetThreadPriority(int priority);
+
+}  // namespace snapshot
+}  // namespace android