typedef struct { ... } *SilcSFTPFilesystem;

    This context is allocated and returned by all filesystem allocation
    routines.  The returned context is given as argument to the
    silc_sftp_server_start function.  The caller must also free the
    context after the SFTP server is shutdown.

    typedef struct {
      SilcSFTPFilesystemOps fs;
      void *fs_context;
    } *SilcSFTPFilesystem;