From: Derrick Stolee <dstolee@xxxxxxxxxxxxx> Edit and expand the sparse-index design document with the plan for guarding index operations with ensure_full_index(). Notably, the plan has changed to not have an expand_to_path() method in favor of checking for a sparse-directory hit inside of the index_path_pos() API. The changes that follow this one will incrementally add ensure_full_index() guards to iterations over all cache entries. Some iterations over the cache entries are not protected due to a few categories listed in the document. Since these are not being modified, here is a short list of the files and methods that will not receive these guards: Looking for non-zero stage: * builtin/add.c:chmod_pathspec() * builtin/merge.c:count_unmerged_entries() * read-cache.c:unmerged_index() * rerere.c:check_one_conflict(), find_conflict(), rerere_remaining() * revision.c:prepare_show_merge() * sequencer.c:append_conflicts_hint() * wt-status.c:wt_status_collect_changes_initial() Looking for submodules: * builtin/submodule--helper.c:module_list_compute() * submodule.c: several methods * worktree.c:validate_no_submodules() Part of the index API: * name-hash.c: lazy init methods * preload-index.c:preload_thread(), preload_index() * read-cache.c: file format methods Checking for correct order of cache entries: * read-cache.c:check_ce_order() Ignores SKIP_WORKTREE entries or already aware: * unpack-trees.c:mark_new_skip_worktree() * wt-status.c:wt_status_check_sparse_checkout() Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx> --- Documentation/technical/sparse-index.txt | 32 +++++++++++++++++++++--- 1 file changed, 29 insertions(+), 3 deletions(-) diff --git a/Documentation/technical/sparse-index.txt b/Documentation/technical/sparse-index.txt index aa116406a016..7ab51bf6c441 100644 --- a/Documentation/technical/sparse-index.txt +++ b/Documentation/technical/sparse-index.txt @@ -82,9 +82,35 @@ also introduce other features that have been considered for improving the index, as well. Next, consumers of the index will be guarded against operating on a -sparse-index by inserting calls to `ensure_full_index()` or -`expand_index_to_path()`. After these guards are in place, we can begin -leaving sparse-directory entries in the in-memory index structure. +sparse-index by inserting calls to `ensure_full_index()` before iterating +over all cache entries. If a specific path is requested, then those will +be protected from within the `index_file_exists()` and `index_name_pos()` +API calls: they will call `ensure_full_index()` if necessary. + +During a scan of the codebase, not every iteration of the cache entries +needs an `ensure_full_index()` check. The basic reasons include: + +1. The loop is scanning for entries with non-zero stage. These entries + are not collapsed into a sparse-directory entry. + +2. The loop is scanning for submodules. These entries are not collapsed + into a sparse-directory entry. + +3. The loop is part of the index API, especially around reading or + writing the format. + +4. The loop is checking for correct order of cache entries and that is + correct if and only if the sparse-directory entries are in the correct + location. + +5. The loop ignores entries with the `SKIP_WORKTREE` bit set, or is + otherwise already aware of sparse directory entries. + +6. The sparse-index is disabled at this point when using the split-index + feature, so no effort is made to protect the split-index API. + +After these guards are in place, we can begin leaving sparse-directory +entries in the in-memory index structure. Even after inserting these guards, we will keep expanding sparse-indexes for most Git commands using the `command_requires_full_index` repository -- gitgitgadget
