text: // Copyright 2015-2019 Espressif Systems (Shanghai) PTE LTD
  //
  // 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 __ESP_VFS_H__
  #define __ESP_VFS_H__
  
  #include <stdint.h>
  #include <stddef.h>
  #include <stdarg.h>
  #include <unistd.h>
  #include <utime.h>
  #include "freertos/FreeRTOS.h"
  #include "freertos/semphr.h"
  #include "esp_err.h"
  #include <sys/types.h>
  #include <sys/reent.h>
  #include <sys/stat.h>
  #include <sys/time.h>
  #include <sys/termios.h>
  #include <sys/poll.h>
  #include <dirent.h>
  #include <string.h>
  #include "sdkconfig.h"
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  #ifndef _SYS_TYPES_FD_SET
  #error "VFS should be used with FD_SETSIZE and FD_SET from sys/types.h"
  #endif
  
  /**
   * Maximum number of (global) file descriptors.
   */
  #define MAX_FDS         FD_SETSIZE /* for compatibility with fd_set and select() */
  
  /**
   * Maximum length of path prefix (not including zero terminator)
   */
  #define ESP_VFS_PATH_MAX 15
  
  /**
   * Default value of flags member in esp_vfs_t structure.
   */
  #define ESP_VFS_FLAG_DEFAULT        0
  
  /**
   * Flag which indicates that FS needs extra context pointer in syscalls.
   */
  #define ESP_VFS_FLAG_CONTEXT_PTR    1
  
  /*
   * @brief VFS identificator used for esp_vfs_register_with_id()
   */
  typedef int esp_vfs_id_t;
  
  /**
   * @brief VFS definition structure
   *
   * This structure should be filled with pointers to corresponding
   * FS driver functions.
   *
   * VFS component will translate all FDs so that the filesystem implementation
   * sees them starting at zero. The caller sees a global FD which is prefixed
   * with an pre-filesystem-implementation.
   *
   * Some FS implementations expect some state (e.g. pointer to some structure)
   * to be passed in as a first argument. For these implementations,
   * populate the members of this structure which have _p suffix, set
   * flags member to ESP_VFS_FLAG_CONTEXT_PTR and provide the context pointer
   * to esp_vfs_register function.
   * If the implementation doesn't use this extra argument, populate the
   * members without _p suffix and set flags member to ESP_VFS_FLAG_DEFAULT.
   *
   * If the FS driver doesn't provide some of the functions, set corresponding
   * members to NULL.
   */
  typedef struct
  {
      int flags;      /*!< ESP_VFS_FLAG_CONTEXT_PTR or ESP_VFS_FLAG_DEFAULT */
      union {
          ssize_t (*write_p)(void* p, int fd, const void * data, size_t size);
          ssize_t (*write)(int fd, const void * data, size_t size);
      };
      union {
          off_t (*lseek_p)(void* p, int fd, off_t size, int mode);
          off_t (*lseek)(int fd, off_t size, int mode);
      };
      union {
          ssize_t (*read_p)(void* ctx, int fd, void * dst, size_t size);
          ssize_t (*read)(int fd, void * dst, size_t size);
      };
      union {
          int (*open_p)(void* ctx, const char * path, int flags, int mode);
          int (*open)(const char * path, int flags, int mode);
      };
      union {
          int (*close_p)(void* ctx, int fd);
          int (*close)(int fd);
      };
      union {
          int (*fstat_p)(void* ctx, int fd, struct stat * st);
          int (*fstat)(int fd, struct stat * st);
      };
      union {
          int (*stat_p)(void* ctx, const char * path, struct stat * st);
          int (*stat)(const char * path, struct stat * st);
      };
      union {
          int (*link_p)(void* ctx, const char* n1, const char* n2);
          int (*link)(const char* n1, const char* n2);
      };
      union {
          int (*unlink_p)(void* ctx, const char *path);
          int (*unlink)(const char *path);
      };
      union {
          int (*rename_p)(void* ctx, const char *src, const char *dst);
          int (*rename)(const char *src, const char *dst);
      };
      union {
          DIR* (*opendir_p)(void* ctx, const char* name);
          DIR* (*opendir)(const char* name);
      };
      union {
          struct dirent* (*readdir_p)(void* ctx, DIR* pdir);
          struct dirent* (*readdir)(DIR* pdir);
      };
      union {
          int (*readdir_r_p)(void* ctx, DIR* pdir, struct dirent* entry, struct dirent** out_dirent);
          int (*readdir_r)(DIR* pdir, struct dirent* entry, struct dirent** out_dirent);
      };
      union {
          long (*telldir_p)(void* ctx, DIR* pdir);
          long (*telldir)(DIR* pdir);
      };
      union {
          void (*seekdir_p)(void* ctx, DIR* pdir, long offset);
          void (*seekdir)(DIR* pdir, long offset);
      };
      union {
          int (*closedir_p)(void* ctx, DIR* pdir);
          int (*closedir)(DIR* pdir);
      };
      union {
          int (*mkdir_p)(void* ctx, const char* name, mode_t mode);
          int (*mkdir)(const char* name, mode_t mode);
      };
      union {
          int (*rmdir_p)(void* ctx, const char* name);
          int (*rmdir)(const char* name);
      };
      union {
          int (*fcntl_p)(void* ctx, int fd, int cmd, va_list args);
          int (*fcntl)(int fd, int cmd, va_list args);
      };
      union {
          int (*ioctl_p)(void* ctx, int fd, int cmd, va_list args);
          int (*ioctl)(int fd, int cmd, va_list args);
      };
      union {
          int (*fsync_p)(void* ctx, int fd);
          int (*fsync)(int fd);
      };
      union {
          int (*access_p)(void* ctx, const char *path, int amode);
          int (*access)(const char *path, int amode);
      };
      union {
          int (*truncate_p)(void* ctx, const char *path, off_t length);
          int (*truncate)(const char *path, off_t length);
      };
      union {
          int (*utime_p)(void* ctx, const char *path, const struct utimbuf *times);
          int (*utime)(const char *path, const struct utimbuf *times);
      };
  #ifdef CONFIG_SUPPORT_TERMIOS
      union {
          int (*tcsetattr_p)(void *ctx, int fd, int optional_actions, const struct termios *p);
          int (*tcsetattr)(int fd, int optional_actions, const struct termios *p);
      };
      union {
          int (*tcgetattr_p)(void *ctx, int fd, struct termios *p);
          int (*tcgetattr)(int fd, struct termios *p);
      };
      union {
          int (*tcdrain_p)(void *ctx, int fd);
          int (*tcdrain)(int fd);
      };
      union {
          int (*tcflush_p)(void *ctx, int fd, int select);
          int (*tcflush)(int fd, int select);
      };
      union {
          int (*tcflow_p)(void *ctx, int fd, int action);
          int (*tcflow)(int fd, int action);
      };
      union {
          pid_t (*tcgetsid_p)(void *ctx, int fd);
          pid_t (*tcgetsid)(int fd);
      };
      union {
          int (*tcsendbreak_p)(void *ctx, int fd, int duration);
          int (*tcsendbreak)(int fd, int duration);
      };
  #endif // CONFIG_SUPPORT_TERMIOS
  
      /** start_select is called for setting up synchronous I/O multiplexing of the desired file descriptors in the given VFS */
      esp_err_t (*start_select)(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, SemaphoreHandle_t *signal_sem);
      /** socket select function for socket FDs with the functionality of POSIX select(); this should be set only for the socket VFS */
      int (*socket_select)(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *timeout);
      /** called by VFS to interrupt the socket_select call when select is activated from a non-socket VFS driver; set only for the socket driver */
      void (*stop_socket_select)();
      /** stop_socket_select which can be called from ISR; set only for the socket driver */
      void (*stop_socket_select_isr)(BaseType_t *woken);
      /** end_select is called to stop the I/O multiplexing and deinitialize the environment created by start_select for the given VFS */
      void* (*get_socket_select_semaphore)();
      /** get_socket_select_semaphore returns semaphore allocated in the socket driver; set only for the socket driver */
      void (*end_select)();
  } esp_vfs_t;
  
  
  /**
   * Register a virtual filesystem for given path prefix.
   *
   * @param base_path  file path prefix associated with the filesystem.
   *                   Must be a zero-terminated C string, up to ESP_VFS_PATH_MAX
   *                   characters long, and at least 2 characters long.
   *                   Name must start with a "/" and must not end with "/".
   *                   For example, "/data" or "/dev/spi" are valid.
   *                   These VFSes would then be called to handle file paths such as
   *                   "/data/myfile.txt" or "/dev/spi/0".
   * @param vfs  Pointer to esp_vfs_t, a structure which maps syscalls to
   *             the filesystem driver functions. VFS component doesn't
   *             assume ownership of this pointer.
   * @param ctx  If vfs->flags has ESP_VFS_FLAG_CONTEXT_PTR set, a pointer
   *             which should be passed to VFS functions. Otherwise, NULL.
   *
   * @return  ESP_OK if successful, ESP_ERR_NO_MEM if too many VFSes are
   *          registered.
   */
  esp_err_t esp_vfs_register(const char* base_path, const esp_vfs_t* vfs, void* ctx);
  
  
  /**
   * Special case function for registering a VFS that uses a method other than
   * open() to open new file descriptors from the interval <min_fd; max_fd).
   *
   * This is a special-purpose function intended for registering LWIP sockets to VFS.
   *
   * @param vfs Pointer to esp_vfs_t. Meaning is the same as for esp_vfs_register().
   * @param ctx Pointer to context structure. Meaning is the same as for esp_vfs_register().
   * @param min_fd The smallest file descriptor this VFS will use.
   * @param max_fd Upper boundary for file descriptors this VFS will use (the biggest file descriptor plus one).
   *
   * @return  ESP_OK if successful, ESP_ERR_NO_MEM if too many VFSes are
   *          registered, ESP_ERR_INVALID_ARG if the file descriptor boundaries
   *          are incorrect.
   */
  esp_err_t esp_vfs_register_fd_range(const esp_vfs_t *vfs, void *ctx, int min_fd, int max_fd);
  
  /**
   * Special case function for registering a VFS that uses a method other than
   * open() to open new file descriptors. In comparison with
   * esp_vfs_register_fd_range, this function doesn't pre-registers an interval
   * of file descriptors. File descriptors can be registered later, by using
   * esp_vfs_register_fd.
   *
   * @param vfs Pointer to esp_vfs_t. Meaning is the same as for esp_vfs_register().
   * @param ctx Pointer to context structure. Meaning is the same as for esp_vfs_register().
   * @param vfs_id Here will be written the VFS ID which can be passed to
   *               esp_vfs_register_fd for registering file descriptors.
   *
   * @return  ESP_OK if successful, ESP_ERR_NO_MEM if too many VFSes are
   *          registered, ESP_ERR_INVALID_ARG if the file descriptor boundaries
   *          are incorrect.
   */
  esp_err_t esp_vfs_register_with_id(const esp_vfs_t *vfs, void *ctx, esp_vfs_id_t *vfs_id);
  
  /**
   * Unregister a virtual filesystem for given path prefix
   *
   * @param base_path  file prefix previously used in esp_vfs_register call
   * @return ESP_OK if successful, ESP_ERR_INVALID_STATE if VFS for given prefix
   *         hasn't been registered
   */
  esp_err_t esp_vfs_unregister(const char* base_path);
  
  /**
   * Special function for registering another file descriptor for a VFS registered
   * by esp_vfs_register_with_id.
   *
   * @param vfs_id VFS identificator returned by esp_vfs_register_with_id.
   * @param fd The registered file descriptor will be written to this address.
   *
   * @return  ESP_OK if the registration is successful,
   *          ESP_ERR_NO_MEM if too many file descriptors are registered,
   *          ESP_ERR_INVALID_ARG if the arguments are incorrect.
   */
  esp_err_t esp_vfs_register_fd(esp_vfs_id_t vfs_id, int *fd);
  
  /**
   * Special function for unregistering a file descriptor belonging to a VFS
   * registered by esp_vfs_register_with_id.
   *
   * @param vfs_id VFS identificator returned by esp_vfs_register_with_id.
   * @param fd File descriptor which should be unregistered.
   *
   * @return  ESP_OK if the registration is successful,
   *          ESP_ERR_INVALID_ARG if the arguments are incorrect.
   */
  esp_err_t esp_vfs_unregister_fd(esp_vfs_id_t vfs_id, int fd);
  
  /**
   * These functions are to be used in newlib syscall table. They will be called by
   * newlib when it needs to use any of the syscalls.
   */
  /**@{*/
  ssize_t esp_vfs_write(struct _reent *r, int fd, const void * data, size_t size);
  off_t esp_vfs_lseek(struct _reent *r, int fd, off_t size, int mode);
  ssize_t esp_vfs_read(struct _reent *r, int fd, void * dst, size_t size);
  int esp_vfs_open(struct _reent *r, const char * path, int flags, int mode);
  int esp_vfs_close(struct _reent *r, int fd);
  int esp_vfs_fstat(struct _reent *r, int fd, struct stat * st);
  int esp_vfs_stat(struct _reent *r, const char * path, struct stat * st);
  int esp_vfs_link(struct _reent *r, const char* n1, const char* n2);
  int esp_vfs_unlink(struct _reent *r, const char *path);
  int esp_vfs_rename(struct _reent *r, const char *src, const char *dst);
  int esp_vfs_utime(const char *path, const struct utimbuf *times);
  /**@}*/
  
  /**
   * @brief Synchronous I/O multiplexing which implements the functionality of POSIX select() for VFS
   * @param nfds      Specifies the range of descriptors which should be checked.
   *                  The first nfds descriptors will be checked in each set.
   * @param readfds   If not NULL, then points to a descriptor set that on input
   *                  specifies which descriptors should be checked for being
   *                  ready to read, and on output indicates which descriptors
   *                  are ready to read.
   * @param writefds  If not NULL, then points to a descriptor set that on input
   *                  specifies which descriptors should be checked for being
   *                  ready to write, and on output indicates which descriptors
   *                  are ready to write.
   * @param errorfds  If not NULL, then points to a descriptor set that on input
   *                  specifies which descriptors should be checked for error
   *                  conditions, and on output indicates which descriptors
   *                  have error conditions.
   * @param timeout   If not NULL, then points to timeval structure which
   *                  specifies the time period after which the functions should
   *                  time-out and return. If it is NULL, then the function will
   *                  not time-out.
   *
   * @return      The number of descriptors set in the descriptor sets, or -1
   *              when an error (specified by errno) have occurred.
   */
  int esp_vfs_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds, struct timeval *timeout);
  
  /**
   * @brief Notification from a VFS driver about a read/write/error condition
   *
   * This function is called when the VFS driver detects a read/write/error
   * condition as it was requested by the previous call to start_select.
   *
   * @param signal_sem semaphore handle which was passed to the driver by the start_select call
   */
  void esp_vfs_select_triggered(SemaphoreHandle_t *signal_sem);
  
  /**
   * @brief Notification from a VFS driver about a read/write/error condition (ISR version)
   *
   * This function is called when the VFS driver detects a read/write/error
   * condition as it was requested by the previous call to start_select.
   *
   * @param signal_sem semaphore handle which was passed to the driver by the start_select call
   * @param woken is set to pdTRUE if the function wakes up a task with higher priority
   */
  void esp_vfs_select_triggered_isr(SemaphoreHandle_t *signal_sem, BaseType_t *woken);
  
  /**
   * @brief Implements the VFS layer for synchronous I/O multiplexing by poll()
   *
   * The implementation is based on esp_vfs_select. The parameters and return values are compatible with POSIX poll().
   *
   * @param fds         Pointer to the array containing file descriptors and events poll() should consider.
   * @param nfds        Number of items in the array fds.
   * @param timeout     Poll() should wait at least timeout milliseconds. If the value is 0 then it should return
   *                    immediately. If the value is -1 then it should wait (block) until the event occurs.
   *
   * @return            A positive return value indicates the number of file descriptors that have been selected. The 0
   *                    return value indicates a timed-out poll. -1 is return on failure and errno is set accordingly.
   *
   */
  int esp_vfs_poll(struct pollfd *fds, nfds_t nfds, int timeout);
  
  #ifdef __cplusplus
  } // extern "C"
  #endif
  
  #endif //__ESP_VFS_H__
  