open_file_map.hpp

/*
  Copyright 2018-2019, Barcelona Supercomputing Center (BSC), Spain
  Copyright 2015-2019, Johannes Gutenberg Universitaet Mainz, Germany

  This software was partially supported by the
  EC H2020 funded project NEXTGenIO (Project ID: 671951, www.nextgenio.eu).

  This software was partially supported by the
  ADA-FS project under the SPPEXA project funded by the DFG.

  SPDX-License-Identifier: MIT
*/


#ifndef GEKKOFS_OPEN_FILE_MAP_HPP
#define GEKKOFS_OPEN_FILE_MAP_HPP

#include <map>
#include <mutex>
#include <memory>
#include <atomic>

/* Forward declaration */
class OpenDir;


enum class OpenFile_flags {
    append = 0,
    creat,
    trunc,
    rdonly,
    wronly,
    rdwr,
    cloexec,
    flag_count // this is purely used as a size variable of this enum class
};

enum class FileType {
    regular,
    directory
};

class OpenFile {
protected:
    FileType type_;
    std::string path_;
    std::array<bool, static_cast<int>(OpenFile_flags::flag_count)> flags_ = {{false}};
    unsigned long pos_;
    std::mutex pos_mutex_;
    std::mutex flag_mutex_;

public:
    // multiple threads may want to update the file position if fd has been duplicated by dup()

    OpenFile(const std::string& path, int flags, FileType type = FileType::regular);

    ~OpenFile();

    // getter/setter
    std::string path() const;

    void path(const std::string& path_);

    unsigned long pos();

    void pos(unsigned long pos_);

    bool get_flag(OpenFile_flags flag);

    void set_flag(OpenFile_flags flag, bool value);

    FileType type() const;
};


class OpenFileMap {

private:
    std::map<int, std::shared_ptr<OpenFile>> files_;
    std::recursive_mutex files_mutex_;

    int safe_generate_fd_idx_();

    /*
     * TODO: Setting our file descriptor index to a specific value is dangerous because we might clash with the kernel.
     * E.g., if we would passthrough and not intercept and the kernel assigns a file descriptor but we will later use
     * the same fd value, we will intercept calls that were supposed to be going to the kernel. This works the other way around too.
     * To mitigate this issue, we set the initial fd number to a high value. We "hope" that we do not clash but this is no permanent solution.
     * Note: This solution will probably work well already for many cases because kernel fd values are reused, unlike to ours.
     * The only case where we will clash with the kernel is, if one process has more than 100000 files open at the same time.
     */
    int fd_idx;
    std::mutex fd_idx_mutex;
    std::atomic<bool> fd_validation_needed;

public:
    OpenFileMap();

    std::shared_ptr<OpenFile> get(int fd);

    std::shared_ptr<OpenDir> get_dir(int dirfd);

    bool exist(int fd);

    int add(std::shared_ptr<OpenFile>);

    bool remove(int fd);

    int dup(int oldfd);

    int dup2(int oldfd, int newfd);

    int generate_fd_idx();
    int get_fd_idx();
};


#endif //GEKKOFS_OPEN_FILE_MAP_HPP