fs_mgr/fs_mgr_boot_config.cpp

/*
 * Copyright (C) 2017 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 <android-base/file.h>
#include <android-base/stringprintf.h>
#include <android-base/strings.h>
#include <android-base/properties.h>

#include "fs_mgr_priv.h"

// Tries to get the boot config value in properties, kernel cmdline and
// device tree (in that order).  returns 'true' if successfully found, 'false'
// otherwise
bool fs_mgr_get_boot_config(const std::string& key, std::string* out_val) {
    FS_MGR_CHECK(out_val != nullptr);

    // first check if we have "ro.boot" property already
    *out_val = android::base::GetProperty("ro.boot." + key, "");
    if (!out_val->empty()) {
        return true;
    }

    // fallback to kernel cmdline, properties may not be ready yet
    std::string cmdline;
    std::string cmdline_key("androidboot." + key);
    if (android::base::ReadFileToString("/proc/cmdline", &cmdline)) {
        for (const auto& entry : android::base::Split(android::base::Trim(cmdline), " ")) {
            std::vector<std::string> pieces = android::base::Split(entry, "=");
            if (pieces.size() == 2) {
                if (pieces[0] == cmdline_key) {
                    *out_val = pieces[1];
                    return true;
                }
            }
        }
    }

    // lastly, check the device tree
    if (is_dt_compatible()) {
        std::string file_name = kAndroidDtDir + "/" + key;
        // DT entries terminate with '\0' but so do the properties
        if (android::base::ReadFileToString(file_name, out_val)) {
            return true;
        }
    }

    return false;
}