Iterate over all tracked submodules of a repository.
See the note on git_submodule
above. This iterates over the tracked
submodules as described therein.
If you are concerned about items in the working directory that look like submodules but are not tracked, the diff API will generate a diff record for workdir items that look like submodules but are not tracked, showing them as added in the workdir. Also, the status API will treat the entire subdirectory of a contained git repo as a single GIT_STATUS_WT_NEW item.
Function to be called with the name of each submodule. Return a non-zero value to terminate the iteration.
Extra data to pass to callback
0 on success, -1 on error, or non-zero return value of callback