extmod/vfs: Guard mutating fs functions with MICROPY_VFS_WRITABLE.

Enabled by default.  Useful for ports that need the VFS but don't have any
writable filesystems.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

extmod/modos.c

@@ -171,13 +171,15 @@ static const mp_rom_map_elem_t os_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_chdir), MP_ROM_PTR(&mp_vfs_chdir_obj) },
     { MP_ROM_QSTR(MP_QSTR_getcwd), MP_ROM_PTR(&mp_vfs_getcwd_obj) },
     { MP_ROM_QSTR(MP_QSTR_listdir), MP_ROM_PTR(&mp_vfs_listdir_obj) },
+    #if MICROPY_VFS_WRITABLE
     { MP_ROM_QSTR(MP_QSTR_mkdir), MP_ROM_PTR(&mp_vfs_mkdir_obj) },
     { MP_ROM_QSTR(MP_QSTR_remove), MP_ROM_PTR(&mp_vfs_remove_obj) },
     { MP_ROM_QSTR(MP_QSTR_rename), MP_ROM_PTR(&mp_vfs_rename_obj) },
     { MP_ROM_QSTR(MP_QSTR_rmdir), MP_ROM_PTR(&mp_vfs_rmdir_obj) },
+    { MP_ROM_QSTR(MP_QSTR_unlink), MP_ROM_PTR(&mp_vfs_remove_obj) }, // unlink aliases to remove
+    #endif
     { MP_ROM_QSTR(MP_QSTR_stat), MP_ROM_PTR(&mp_vfs_stat_obj) },
     { MP_ROM_QSTR(MP_QSTR_statvfs), MP_ROM_PTR(&mp_vfs_statvfs_obj) },
-    { MP_ROM_QSTR(MP_QSTR_unlink), MP_ROM_PTR(&mp_vfs_remove_obj) }, // unlink aliases to remove
     #endif
 
     // The following are MicroPython extensions.

extmod/vfs.c

@@ -443,6 +443,8 @@ mp_obj_t mp_vfs_listdir(size_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_vfs_listdir_obj, 0, 1, mp_vfs_listdir);
 
+#if MICROPY_VFS_WRITABLE
+
 mp_obj_t mp_vfs_mkdir(mp_obj_t path_in) {
     mp_obj_t path_out;
     mp_vfs_mount_t *vfs = lookup_path(path_in, &path_out);
@@ -479,6 +481,8 @@ mp_obj_t mp_vfs_rmdir(mp_obj_t path_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_1(mp_vfs_rmdir_obj, mp_vfs_rmdir);
 
+#endif // MICROPY_VFS_WRITABLE
+
 mp_obj_t mp_vfs_stat(mp_obj_t path_in) {
     mp_obj_t path_out;
     mp_vfs_mount_t *vfs = lookup_path(path_in, &path_out);

extmod/vfs.h

@@ -95,10 +95,12 @@ mp_obj_t mp_vfs_chdir(mp_obj_t path_in);
 mp_obj_t mp_vfs_getcwd(void);
 mp_obj_t mp_vfs_ilistdir(size_t n_args, const mp_obj_t *args);
 mp_obj_t mp_vfs_listdir(size_t n_args, const mp_obj_t *args);
+#if MICROPY_VFS_WRITABLE
 mp_obj_t mp_vfs_mkdir(mp_obj_t path_in);
 mp_obj_t mp_vfs_remove(mp_obj_t path_in);
 mp_obj_t mp_vfs_rename(mp_obj_t old_path_in, mp_obj_t new_path_in);
 mp_obj_t mp_vfs_rmdir(mp_obj_t path_in);
+#endif
 mp_obj_t mp_vfs_stat(mp_obj_t path_in);
 mp_obj_t mp_vfs_statvfs(mp_obj_t path_in);
 
@@ -111,10 +113,12 @@ MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_chdir_obj);
 MP_DECLARE_CONST_FUN_OBJ_0(mp_vfs_getcwd_obj);
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_vfs_ilistdir_obj);
 MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_vfs_listdir_obj);
+#if MICROPY_VFS_WRITABLE
 MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_mkdir_obj);
 MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_remove_obj);
 MP_DECLARE_CONST_FUN_OBJ_2(mp_vfs_rename_obj);
 MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_rmdir_obj);
+#endif
 MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_stat_obj);
 MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_statvfs_obj);
 

py/mpconfig.h

@@ -991,6 +991,11 @@ typedef double mp_float_t;
 #define MICROPY_VFS (0)
 #endif
 
+// Whether to include support for writable filesystems.
+#ifndef MICROPY_VFS_WRITABLE
+#define MICROPY_VFS_WRITABLE (1)
+#endif
+
 // Support for VFS POSIX component, to mount a POSIX filesystem within VFS
 #ifndef MICROPY_VFS_POSIX
 #define MICROPY_VFS_POSIX (0)