apex/apexd/apex_database.h

/*
 * Copyright (C) 2018 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.
 */

#ifndef ANDROID_APEXD_APEX_DATABASE_H_
#define ANDROID_APEXD_APEX_DATABASE_H_

#include <android-base/logging.h>
#include <android-base/result.h>
#include <android-base/thread_annotations.h>

#include <map>
#include <mutex>
#include <optional>
#include <set>
#include <string>
#include <unordered_set>

namespace android {
namespace apex {

class MountedApexDatabase {
 public:
  // Stores associated low-level data for a mounted APEX. To conserve memory,
  // the APEX file isn't stored, but must be opened to retrieve specific data.
  struct MountedApexData {
    int version = 0;        // APEX version for this mount
    std::string loop_name;  // Loop device used (fs path).
    std::string full_path;  // Full path to the apex file.
    std::string mount_point;  // Path this apex is mounted on.
    std::string device_name;  // Name of the dm verity device.
    // Whenever apex file specified in full_path was deleted.
    bool deleted = false;

    MountedApexData() = default;
    MountedApexData(int version, const std::string& loop_name,
                    const std::string& full_path,
                    const std::string& mount_point,
                    const std::string& device_name)
        : version(version),
          loop_name(loop_name),
          full_path(full_path),
          mount_point(mount_point),
          device_name(device_name),
          deleted(false) {}

    inline auto operator<=>(const MountedApexData& rhs) const = default;
  };

  template <typename... Args>
  inline void AddMountedApexLocked(const std::string& package, Args&&... args)
      REQUIRES(mounted_apexes_mutex_) {
    auto [_, inserted] =
        mounted_apexes_[package].emplace(std::forward<Args>(args)...);
    CHECK(inserted);
  }

  template <typename... Args>
  inline void AddMountedApex(const std::string& package, Args&&... args)
      REQUIRES(!mounted_apexes_mutex_) {
    std::lock_guard lock(mounted_apexes_mutex_);
    AddMountedApexLocked(package, std::forward<Args>(args)...);
  }

  inline void RemoveMountedApex(const std::string& package,
                                const std::string& full_path)
      REQUIRES(!mounted_apexes_mutex_) {
    std::lock_guard lock(mounted_apexes_mutex_);
    auto it = mounted_apexes_.find(package);
    if (it == mounted_apexes_.end()) {
      return;
    }

    auto& pkg_set = it->second;

    for (auto pkg_it = pkg_set.begin(); pkg_it != pkg_set.end(); ++pkg_it) {
      if (pkg_it->full_path == full_path) {
        pkg_set.erase(pkg_it);
        return;
      }
    }
  }

  // Invoke handler if the passed package is the latest
  inline base::Result<void> DoIfLatest(
      const std::string& package, const std::string& full_path,
      const std::function<base::Result<void>()>& handler)
      REQUIRES(!mounted_apexes_mutex_) {
    std::lock_guard lock(mounted_apexes_mutex_);
    auto it = mounted_apexes_.find(package);
    CHECK(it != mounted_apexes_.end());
    CHECK(!it->second.empty());

    auto latest = it->second.rbegin();
    if (latest->full_path == full_path) {
      return handler();
    }
    return {};
  }

  template <typename T>
  inline void ForallMountedApexes(const std::string& package,
                                  const T& handler) const
      REQUIRES(!mounted_apexes_mutex_) {
    std::lock_guard lock(mounted_apexes_mutex_);
    auto outer_it = mounted_apexes_.find(package);
    if (outer_it == mounted_apexes_.end()) {
      return;
    }
    for (auto it = outer_it->second.rbegin(), end = outer_it->second.rend();
         it != end; it++) {
      bool latest = (it == outer_it->second.rbegin());
      handler(*it, latest);
    }
  }

  template <typename T>
  inline void ForallMountedApexes(const T& handler) const
      REQUIRES(!mounted_apexes_mutex_) {
    std::lock_guard lock(mounted_apexes_mutex_);
    for (const auto& pkg : mounted_apexes_) {
      for (auto it = pkg.second.rbegin(), end = pkg.second.rend(); it != end;
           it++) {
        bool latest = (it == pkg.second.rbegin());
        handler(pkg.first, *it, latest);
      }
    }
  }

  inline std::optional<MountedApexData> GetLatestMountedApex(
      const std::string& package) const REQUIRES(!mounted_apexes_mutex_) {
    std::optional<MountedApexData> ret;
    ForallMountedApexes(package,
                        [&ret](const MountedApexData& data, bool latest) {
                          if (latest) {
                            ret.emplace(data);
                          }
                        });
    return ret;
  }

  void PopulateFromMounts(const std::vector<std::string>& data_dirs);

  // Resets state of the database. Should only be used in testing.
  inline void Reset() REQUIRES(!mounted_apexes_mutex_) {
    std::lock_guard lock(mounted_apexes_mutex_);
    mounted_apexes_.clear();
  }

 private:
  // A map from package name to mounted apexes.
  // Note: using std::maps to
  //         a) so we do not have to worry about iterator invalidation.
  //         b) do not have to const_cast (over std::set)
  // TODO(b/158467745): This structure (and functions) need to be guarded by
  //   locks.
  std::map<std::string, std::set<MountedApexData>> mounted_apexes_
      GUARDED_BY(mounted_apexes_mutex_);

  // To fix thread safety negative capability warning
  class Mutex : public std::mutex {
   public:
    // for negative capabilities
    const Mutex& operator!() const { return *this; }
  };
  mutable Mutex mounted_apexes_mutex_;
};

}  // namespace apex
}  // namespace android

#endif  // ANDROID_APEXD_APEX_DATABASE_H_