Allow fetching from the submodule's default remote if the target commit isn't found. Enabled by default.
These options are passed to the checkout step. To disable checkout, set the checkout_strategy to git_checkout_strategy_t.GIT_CHECKOUT_NONE. Generally you will want the use git_checkout_strategy_t.GIT_CHECKOUT_SAFE to update files in the working directory.
Options which control the fetch, including callbacks.
Submodule update options structure
Initialize with GIT_SUBMODULE_UPDATE_OPTIONS_INIT. Alternatively, you can use git_submodule_update_options_init.