typedef struct SilcSFTPFilesystemOpsStruct { ... }
                     *SilcSFTPFilesystemOps;

    This structure defines the generic filesystem access.  When the
    filesystem is accessed these functions are called to do the requested
    filesystem operation.  The level that implements the actual filesystem
    must fill this structure with the callback functions providing the
    access to the filesystem.

    typedef struct SilcSFTPFilesystemOpsStruct {
      /* Find a file handle by the file handle data indicated by the `data'.
         If the handle is not found this returns NULL. */
      SilcSFTPHandle (*sftp_get_handle)(void *context, SilcSFTP sftp,
                                        const unsigned char *data,
                                        SilcUInt32 data_len);
    
      /* Return encoded handle of `handle' or NULL on error. The caller
         must free the returned buffer. */
      unsigned char *(*sftp_encode_handle)(void *context, SilcSFTP sftp,
                                           SilcSFTPHandle handle,
                                           SilcUInt32 *handle_len);
    
      /* Open a file indicated by the `filename' with flags indicated by the
         `pflags', and with attributes indicated by the `attr'.  Calls the
         `callback' to return the opened file handle. */
      void (*sftp_open)(void *context, SilcSFTP sftp,
                        const char *filename,
                        SilcSFTPFileOperation pflags,
                        SilcSFTPAttributes attr,
                        SilcSFTPHandleCallback callback,
                        void *callback_context);
    
      /* Closes the file indicated by the file handle `handle'.  Calls the
         `callback' to indicate the status of the closing. */
      void (*sftp_close)(void *context, SilcSFTP sftp,
                         SilcSFTPHandle handle,
                         SilcSFTPStatusCallback callback,
                         void *callback_context);
    
      /* Reads data from the file indicated by the file handle `handle' starting
         from the offset of `offset' at most `len' bytes.  The `callback' is
         called to return the read data. */
      void (*sftp_read)(void *context, SilcSFTP sftp,
                        SilcSFTPHandle handle,
                        SilcUInt64 offset,
                        SilcUInt32 len,
                        SilcSFTPDataCallback callback,
                        void *callback_context);
    
      /* Writes to a file indicated by the file handle `handle' starting from
         offset of `offset' at most `data_len' bytes of `data'.  The `callback'
         is called to indicate the status of the writing. */
      void (*sftp_write)(void *context, SilcSFTP sftp,
                         SilcSFTPHandle handle,
                         SilcUInt64 offset,
                         const unsigned char *data,
                         SilcUInt32 data_len,
                         SilcSFTPStatusCallback callback,
                         void *callback_context);
    
      /* Removes a file indicated by the `filename'.  Calls the `callback'
         to indicate the status of the removing. */
      void (*sftp_remove)(void *context, SilcSFTP sftp,
                          const char *filename,
                          SilcSFTPStatusCallback callback,
                          void *callback_context);
    
      /* Renames a file indicated by the `oldname' to the name `newname'.  The
         `callback' is called to indicate the status of the renaming. */
      void (*sftp_rename)(void *context, SilcSFTP sftp,
                          const char *oldname,
                          const char *newname,
                          SilcSFTPStatusCallback callback,
                          void *callback_context);
    
      /* Creates a new directory indicated by the `path' with attributes indicated
         by the `attrs'. The `callback' is called to indicate the status of the
         creation. */
      void (*sftp_mkdir)(void *context, SilcSFTP sftp,
                         const char *path,
                         SilcSFTPAttributes attrs,
                         SilcSFTPStatusCallback callback,
                         void *callback_context);
    
      /* Removes a directory indicated by the `path' and calls the `callback'
         to indicate the status of the removal. */
      void (*sftp_rmdir)(void *context, SilcSFTP sftp,
                         const char *path,
                         SilcSFTPStatusCallback callback,
                         void *callback_context);
    
      /* Opens a directory indicated by the `path'.  The `callback' is called
         to return the opened file handle. */
      void (*sftp_opendir)(void *context, SilcSFTP sftp,
                           const char *path,
                           SilcSFTPHandleCallback callback,
                           void *callback_context);
    
      /* Reads the contents of the directory indicated by the `handle' and
         calls the `callback' to return the read file(s) from the directory. */
      void (*sftp_readdir)(void *context, SilcSFTP sftp,
                           SilcSFTPHandle handle,
                           SilcSFTPNameCallback callback,
                           void *callback_context);
    
      /* Gets the file attributes for a file indicated by the `path'. This
         will follow symbolic links also. Calls the `callback' to return the
         file attributes. */
      void (*sftp_stat)(void *context, SilcSFTP sftp,
                        const char *path,
                        SilcSFTPAttrCallback callback,
                        void *callback_context);
    
      /* Gets the file attributes for a file indicated by the `path'. This
         will not follow symbolic links. Calls the `callback' to return the
         file attributes. */
      void (*sftp_lstat)(void *context, SilcSFTP sftp,
                         const char *path,
                         SilcSFTPAttrCallback callback,
                         void *callback_context);
    
      /* Gets a file attributes for a opened file indicated by the `handle'.
         Calls the `callback' to return the file attributes. */
      void (*sftp_fstat)(void *context, SilcSFTP sftp,
                         SilcSFTPHandle handle,
                         SilcSFTPAttrCallback callback,
                         void *callback_context);
    
      /* Sets a file attributes to a file indicated by the `path' with the
         attributes indicated by the `attrs'.  Calls the `callback' to indicate
         the status of the setting. */
      void (*sftp_setstat)(void *context, SilcSFTP sftp,
                           const char *path,
                           SilcSFTPAttributes attrs,
                           SilcSFTPStatusCallback callback,
                           void *callback_context);
    
      /* Sets a file attributes to a opened file indicated by the `handle' with
         the attributes indicated by the `attrs'.  Calls the `callback' to
         indicate the status of the setting. */
      void (*sftp_fsetstat)(void *context, SilcSFTP sftp,
                            SilcSFTPHandle handle,
                            SilcSFTPAttributes attrs,
                            SilcSFTPStatusCallback callback,
                            void *callback_context);
    
      /* Reads the target of a symbolic link indicated by the `path'.  The
         `callback' is called to return the target of the symbolic link. */
      void (*sftp_readlink)(void *context, SilcSFTP sftp,
                            const char *path,
                            SilcSFTPNameCallback callback,
                            void *callback_context);
    
      /* Creates a new symbolic link indicated by the `linkpath' to the target
         indicated by the `targetpath'.  The `callback' is called to indicate
         the status of creation. */
      void (*sftp_symlink)(void *context, SilcSFTP sftp,
                           const char *linkpath,
                           const char *targetpath,
                           SilcSFTPStatusCallback callback,
                           void *callback_context);
    
      /* Canonicalizes the path indicated by the `path' to a absolute path.
         The `callback' is called to return the absolute path. */
      void (*sftp_realpath)(void *context, SilcSFTP sftp,
                            const char *path,
                            SilcSFTPNameCallback callback,
                            void *callback_context);
    
      /* Performs an extended operation indicated by the `request' with
         optional extended operation data indicated by the `data'.  The callback
         is called to return any data associated with the extended request. */
      void (*sftp_extended)(void *context, SilcSFTP sftp,
                            const char *request,
                            const unsigned char *data,
                            SilcUInt32 data_len,
                            SilcSFTPExtendedCallback callback,
                            void *callback_context);
    } *SilcSFTPFilesystemOps;