extmod/vfs: Add mp_vfs_mount_romfs_protected() helper.

This function will attempt to create a `VfsRom` instance and mount it at
location "/rom" in the filesystem.

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

Author: dpgeorge

extmod/vfs.c

@@ -46,6 +46,10 @@
 #include "extmod/vfs_posix.h"
 #endif
 
+#if MICROPY_VFS_ROM && MICROPY_VFS_ROM_IOCTL
+#include "extmod/vfs_rom.h"
+#endif
+
 // For mp_vfs_proxy_call, the maximum number of additional args that can be passed.
 // A fixed maximum size is used to avoid the need for a costly variable array.
 #define PROXY_MAX_ARGS (2)
@@ -552,6 +556,32 @@ int mp_vfs_mount_and_chdir_protected(mp_obj_t bdev, mp_obj_t mount_point) {
     return ret;
 }
 
+#if MICROPY_VFS_ROM && MICROPY_VFS_ROM_IOCTL
+
+int mp_vfs_mount_romfs_protected(void) {
+    int ret;
+    nlr_buf_t nlr;
+    if (nlr_push(&nlr) == 0) {
+        mp_obj_t args[2] = { MP_OBJ_NEW_SMALL_INT(MP_VFS_ROM_IOCTL_GET_SEGMENT), MP_OBJ_NEW_SMALL_INT(0) };
+        mp_obj_t rom = mp_vfs_rom_ioctl(2, args);
+        mp_obj_t romfs = mp_call_function_1(MP_OBJ_FROM_PTR(&mp_type_vfs_rom), rom);
+        mp_obj_t mount_point = MP_OBJ_NEW_QSTR(MP_QSTR__slash_rom);
+        mp_call_function_2(MP_OBJ_FROM_PTR(&mp_vfs_mount_obj), romfs, mount_point);
+        #if MICROPY_PY_SYS_PATH_ARGV_DEFAULTS
+        // Add "/rom" and "/rom/lib" to `sys.path`.
+        mp_obj_list_append(mp_sys_path, MP_OBJ_NEW_QSTR(MP_QSTR__slash_rom));
+        mp_obj_list_append(mp_sys_path, MP_OBJ_NEW_QSTR(MP_QSTR__slash_rom_slash_lib));
+        #endif
+        ret = 0; // success
+        nlr_pop();
+    } else {
+        ret = -MP_EIO;
+    }
+    return ret;
+}
+
+#endif
+
 MP_REGISTER_ROOT_POINTER(struct _mp_vfs_mount_t *vfs_cur);
 MP_REGISTER_ROOT_POINTER(struct _mp_vfs_mount_t *vfs_mount_table);
 

extmod/vfs.h

@@ -112,6 +112,9 @@ mp_obj_t mp_vfs_stat(mp_obj_t path_in);
 mp_obj_t mp_vfs_statvfs(mp_obj_t path_in);
 
 int mp_vfs_mount_and_chdir_protected(mp_obj_t bdev, mp_obj_t mount_point);
+#if MICROPY_VFS_ROM && MICROPY_VFS_ROM_IOCTL
+int mp_vfs_mount_romfs_protected(void);
+#endif
 
 MP_DECLARE_CONST_FUN_OBJ_KW(mp_vfs_mount_obj);
 MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_umount_obj);

py/qstrdefs.h

@@ -68,6 +68,11 @@ Q(utf-8)
 Q(.frozen)
 #endif
 
+#if MICROPY_VFS_ROM && MICROPY_VFS_ROM_IOCTL
+Q(/rom)
+Q(/rom/lib)
+#endif
+
 #if MICROPY_ENABLE_PYSTACK
 Q(pystack exhausted)
 #endif