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 <algorithm>
#include <iterator>
#include <string>
#include <vector>

#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"

std::vector<std::pair<std::string, std::string>> fs_mgr_parse_boot_config(const std::string& cmdline) {
    static constexpr char quote = '"';

    std::vector<std::pair<std::string, std::string>> result;
    size_t base = 0;
    while (true) {
        // skip quoted spans
        auto found = base;
        while (((found = cmdline.find_first_of(" \"", found)) != cmdline.npos) &&
               (cmdline[found] == quote)) {
            // unbalanced quote is ok
            if ((found = cmdline.find(quote, found + 1)) == cmdline.npos) break;
            ++found;
        }
        std::string piece;
        auto source = cmdline.substr(base, found - base);
        std::remove_copy(source.begin(), source.end(),
                         std::back_insert_iterator<std::string>(piece), quote);
        auto equal_sign = piece.find('=');
        if (equal_sign == piece.npos) {
            if (!piece.empty()) {
                // no difference between <key> and <key>=
                result.emplace_back(std::move(piece), "");
            }
        } else {
            result.emplace_back(piece.substr(0, equal_sign), piece.substr(equal_sign + 1));
        }
        if (found == cmdline.npos) break;
        base = found + 1;
    }

    return result;
}

bool fs_mgr_get_boot_config_from_kernel(const std::string& cmdline, const std::string& android_key,
                                        std::string* out_val) {
    FS_MGR_CHECK(out_val != nullptr);

    const std::string cmdline_key("androidboot." + android_key);
    for (const auto& [key, value] : fs_mgr_parse_boot_config(cmdline)) {
        if (key == cmdline_key) {
            *out_val = value;
            return true;
        }
    }

    *out_val = "";
    return false;
}

// Tries to get the given boot config value from kernel cmdline.
// Returns true if successfully found, false otherwise.
bool fs_mgr_get_boot_config_from_kernel_cmdline(const std::string& key, std::string* out_val) {
    std::string cmdline;
    if (!android::base::ReadFileToString("/proc/cmdline", &cmdline)) return false;
    if (!cmdline.empty() && cmdline.back() == '\n') {
        cmdline.pop_back();
    }
    return fs_mgr_get_boot_config_from_kernel(cmdline, key, out_val);
}

// Tries to get the boot config value in device tree, properties and
// kernel cmdline (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);

    // firstly, check the device tree
    if (is_dt_compatible()) {
        std::string file_name = get_android_dt_dir() + "/" + key;
        if (android::base::ReadFileToString(file_name, out_val)) {
            if (!out_val->empty()) {
                out_val->pop_back();  // Trims the trailing '\0' out.
                return true;
            }
        }
    }

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

    // finally, fallback to kernel cmdline, properties may not be ready yet
    if (fs_mgr_get_boot_config_from_kernel_cmdline(key, out_val)) {
        return true;
    }

    return false;
}