ardupilot/libraries/AP_Filesystem/AP_Filesystem_ROMFS.h

/*
   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#pragma once

#include "AP_Filesystem_backend.h"

class AP_Filesystem_ROMFS : public AP_Filesystem_Backend
{
public:
    // functions that closely match the equivalent posix calls
    int open(const char *fname, int flags, bool allow_absolute_paths = false) override;
    int close(int fd) override;
    int32_t read(int fd, void *buf, uint32_t count) override;
    int32_t write(int fd, const void *buf, uint32_t count) override;
    int fsync(int fd) override;
    int32_t lseek(int fd, int32_t offset, int whence) override;
    int stat(const char *pathname, struct stat *stbuf) override;
    int unlink(const char *pathname) override;
    int mkdir(const char *pathname) override;
    void *opendir(const char *pathname) override;
    struct dirent *readdir(void *dirp) override;
    int closedir(void *dirp) override;

    // return free disk space in bytes, -1 on error
    int64_t disk_free(const char *path) override;

    // return total disk space in bytes, -1 on error
    int64_t disk_space(const char *path) override;

    // set modification time on a file
    bool set_mtime(const char *filename, const uint32_t mtime_sec) override;

    /*
      load a full file. Use delete to free the data
     */
    FileData *load_file(const char *filename) override;

    // unload data from load_file()
    void unload_file(FileData *fd) override;
    
private:
    // only allow up to 4 files at a time
    static constexpr uint8_t max_open_file = 4;
    static constexpr uint8_t max_open_dir = 4;
    struct rfile {
        const uint8_t *data;
        uint32_t size;
        uint32_t ofs;
    } file[max_open_file];

    // allow up to 4 directory opens
    struct rdir {
        char *path;
        uint16_t ofs;
        struct dirent de;
    } dir[max_open_dir];
};