cvd: Add support for logging to a file

Implement timestamped log file creation for the cvd command. Logs are
saved in PerUserDir() + "/logs/" with a name like
cvd_YYYYMMDD_HHMMSS.ms.log. This ensures logs are preserved across runs.

Assisted-by: Jetski <jetski@google.com>
Bug: b/507600500

Author: Databean

base/cvd/cuttlefish/host/commands/cvd/BUILD.bazel

@@ -35,6 +35,7 @@ cf_cc_binary(
         "//cuttlefish/common/libs/utils:flag_parser",
         "//cuttlefish/common/libs/utils:subprocess",
         "//cuttlefish/common/libs/utils:tee_logging",
+        "//cuttlefish/host/commands/cvd/cli:log_files",
         "//cuttlefish/host/commands/cvd/utils",
         "//cuttlefish/host/commands/cvd/version",
         "//cuttlefish/host/libs/vm_manager",

base/cvd/cuttlefish/host/commands/cvd/cli/BUILD.bazel

@@ -51,6 +51,17 @@ cf_cc_library(
     ],
 )
 
+cf_cc_library(
+    name = "log_files",
+    srcs = ["log_files.cpp"],
+    hdrs = ["log_files.h"],
+    deps = [
+        "//cuttlefish/common/libs/utils:files",
+        "//cuttlefish/host/commands/cvd/utils",
+        "@abseil-cpp//absl/strings",
+    ],
+)
+
 # Commands that may invoke other commands
 cf_cc_library(
     name = "nesting_commands",

base/cvd/cuttlefish/host/commands/cvd/cli/log_files.cpp

@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2026 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 "cuttlefish/host/commands/cvd/cli/log_files.h"
+
+#include <chrono>
+#include <iomanip>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <vector>
+
+#include "absl/strings/str_cat.h"
+
+#include "cuttlefish/common/libs/utils/files.h"
+#include "cuttlefish/host/commands/cvd/utils/common.h"
+
+namespace cuttlefish {
+
+std::optional<std::string> GetLogFile() {
+  std::string log_dir = PerUserDir() + "/logs";
+  if (!EnsureDirectoryExists(log_dir, 0777).ok()) {
+    std::cerr << "Failed to create log directory: " << log_dir
+              << ". Logging to file disabled." << std::endl;
+    return std::nullopt;
+  }
+
+  std::chrono::system_clock::time_point now = std::chrono::system_clock::now();
+  std::time_t now_time_t = std::chrono::system_clock::to_time_t(now);
+  std::chrono::milliseconds now_ms =
+      std::chrono::duration_cast<std::chrono::milliseconds>(
+          now.time_since_epoch()) %
+      1000;
+
+  std::tm tm_now;
+  localtime_r(&now_time_t, &tm_now);
+
+  std::stringstream ss;
+  ss << std::put_time(&tm_now, "%Y%m%d_%H%M%S") << "." << std::setfill('0')
+     << std::setw(3) << now_ms.count();
+  return absl::StrCat(log_dir, "/cvd_", ss.str(), ".log");
+}
+
+}  // namespace cuttlefish

base/cvd/cuttlefish/host/commands/cvd/cli/log_files.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2026 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
+
+#include <optional>
+#include <string>
+
+namespace cuttlefish {
+
+/**
+ * Returns the path to a new timestamped log file for the
+ * cvd command. The log file is created in PerUserDir() + "/logs/" with a name
+ * like cvd_YYYYMMDD_HHMMSS.ms.log. If the logs directory cannot be created, the
+ * function returns std::nullopt.
+ */
+std::optional<std::string> GetLogFile();
+
+}  // namespace cuttlefish

base/cvd/cuttlefish/host/commands/cvd/main.cc

@@ -26,17 +26,18 @@
 #include <unordered_map>
 #include <vector>
 
-#include <android-base/file.h>
 #include "absl/cleanup/cleanup.h"
-#include "absl/strings/str_split.h"
-#include <fmt/format.h>
 #include "absl/log/log.h"
+#include "absl/strings/str_split.h"
+#include "android-base/file.h"
+#include "fmt/format.h"
 
 #include "cuttlefish/common/libs/utils/environment.h"
 #include "cuttlefish/common/libs/utils/files.h"
 #include "cuttlefish/common/libs/utils/flag_parser.h"
 #include "cuttlefish/common/libs/utils/subprocess.h"
 #include "cuttlefish/common/libs/utils/tee_logging.h"
+#include "cuttlefish/host/commands/cvd/cli/log_files.h"
 #include "cuttlefish/host/commands/cvd/cvd.h"
 #include "cuttlefish/host/commands/cvd/utils/common.h"
 #include "cuttlefish/host/commands/cvd/version/version.h"
@@ -216,6 +217,7 @@ bool ValidateHostConfiguration() {
 }
 
 }  // namespace
+
 }  // namespace cuttlefish
 
 int main(int argc, char** argv) {
@@ -228,7 +230,13 @@ int main(int argc, char** argv) {
   cuttlefish::MetadataLevel metadata_level =
       isatty(0) ? cuttlefish::MetadataLevel::ONLY_MESSAGE
                 : cuttlefish::MetadataLevel::FULL;
-  cuttlefish::LogToStderr("", metadata_level, verbosity);
+
+  std::optional<std::string> log_file = cuttlefish::GetLogFile();
+  std::vector<std::string> log_files;
+  if (log_file) {
+    log_files.push_back(*log_file);
+  }
+  cuttlefish::LogToStderrAndFiles(log_files, "", metadata_level, verbosity);
 
   if (!cuttlefish::ValidateHostConfiguration()) {
     return -1;