Re: [PATCH 10/19] reset --keep: only write index file once

> "git reset --keep" calls reset_index_file() twice, first doing a
> two-way merge to the target revision, updating the index and worktree,
> and then resetting the index. After each call, we write the index
> file.
>
> In the unlikely event that the second call to reset_index_file()
> fails, the index will have been merged to the target revision, but
> HEAD will not be updated, leaving the user with a dirty index.
>
> By moving the locking, writing and committing out of
> reset_index_file() and into the caller, we can avoid writing the index
> twice, thereby making the sure we don't end up in the half-way reset
> state.