On Fri, May 20, 2022 at 12:29 PM Goss Geppert <gg.oss.dev@xxxxxxxxx> wrote:
>
> When traversing the directory tree, the realpath of the `git_dir` is
> required each time a nested repository is encountered to determine how
> the nested repository should be treated. To prevent excessive resource
> usage in pathological cases (e.g. many nested repositories, a long path,
> symlinks, etc.), cache the realpath after the first usage until the
> traversal is complete.
> ---
> dir.c | 63 ++++++++++++++++++++++++++++++++++++++++-------------------
> 1 file changed, 43 insertions(+), 20 deletions(-)
>
> diff --git a/dir.c b/dir.c
> index e45e117875..45b89560fc 100644
> --- a/dir.c
> +++ b/dir.c
> @@ -47,10 +47,22 @@ struct cached_dir {
> struct untracked_cache_dir *ucd;
> };
>
> +/*
> + * Support data structure for the recursing into the directory tree.
> + */
> +struct traversal_cache {
> + /*
> + * The realpath for the `git_dir` may be required in the recursion and is
> + * cached for repeated use.
> + */
> + char *real_gitdir;
> +};
> +
> static enum path_treatment read_directory_recursive(struct dir_struct *dir,
> struct index_state *istate, const char *path, int len,
> struct untracked_cache_dir *untracked,
> - int check_only, int stop_at_first_file, const struct pathspec *pathspec);
> + int check_only, int stop_at_first_file, const struct pathspec *pathspec,
> + struct traversal_cache *cache);
> static int resolve_dtype(int dtype, struct index_state *istate,
> const char *path, int len);
> struct dirent *readdir_skip_dot_and_dotdot(DIR *dirp)
> @@ -1852,7 +1864,8 @@ static enum path_treatment treat_directory(struct dir_struct *dir,
> struct index_state *istate,
> struct untracked_cache_dir *untracked,
> const char *dirname, int len, int baselen, int excluded,
> - const struct pathspec *pathspec)
> + const struct pathspec *pathspec,
> + struct traversal_cache *cache)
> {
> /*
> * WARNING: From this function, you can return path_recurse or you
> @@ -1906,13 +1919,13 @@ static enum path_treatment treat_directory(struct dir_struct *dir,
> nested_repo = is_nonbare_repository_dir(&sb);
>
> if (nested_repo) {
> - char *real_dirname, *real_gitdir;
> + char *real_dirname;
> strbuf_addstr(&sb, ".git");
> real_dirname = real_pathdup(sb.buf, 1);
> - real_gitdir = real_pathdup(the_repository->gitdir, 1);
> + if (!cache->real_gitdir)
> + cache->real_gitdir = real_pathdup(the_repository->gitdir, 1);
>
> - nested_repo = !!strcmp(real_dirname, real_gitdir);
> - free(real_gitdir);
> + nested_repo = !!strcmp(real_dirname, cache->real_gitdir);
> free(real_dirname);
> }
> strbuf_release(&sb);
> @@ -1944,7 +1957,7 @@ static enum path_treatment treat_directory(struct dir_struct *dir,
> return path_excluded;
>
> if (read_directory_recursive(dir, istate, dirname, len,
> - untracked, 1, 1, pathspec) == path_excluded)
> + untracked, 1, 1, pathspec, cache) == path_excluded)
> return path_excluded;
>
> return path_none;
> @@ -2045,7 +2058,7 @@ static enum path_treatment treat_directory(struct dir_struct *dir,
> untracked = lookup_untracked(dir->untracked, untracked,
> dirname + baselen, len - baselen);
> state = read_directory_recursive(dir, istate, dirname, len, untracked,
> - check_only, stop_early, pathspec);
> + check_only, stop_early, pathspec, cache);
>
> /* There are a variety of reasons we may need to fixup the state... */
> if (state == path_excluded) {
> @@ -2242,7 +2255,8 @@ static enum path_treatment treat_path_fast(struct dir_struct *dir,
> struct index_state *istate,
> struct strbuf *path,
> int baselen,
> - const struct pathspec *pathspec)
> + const struct pathspec *pathspec,
> + struct traversal_cache *cache)
> {
> /*
> * WARNING: From this function, you can return path_recurse or you
> @@ -2264,7 +2278,7 @@ static enum path_treatment treat_path_fast(struct dir_struct *dir,
> * with check_only set.
> */
> return read_directory_recursive(dir, istate, path->buf, path->len,
> - cdir->ucd, 1, 0, pathspec);
> + cdir->ucd, 1, 0, pathspec, cache);
> /*
> * We get path_recurse in the first run when
> * directory_exists_in_index() returns index_nonexistent. We
> @@ -2280,13 +2294,14 @@ static enum path_treatment treat_path(struct dir_struct *dir,
> struct index_state *istate,
> struct strbuf *path,
> int baselen,
> - const struct pathspec *pathspec)
> + const struct pathspec *pathspec,
> + struct traversal_cache *cache)
> {
> int has_path_in_index, dtype, excluded;
>
> if (!cdir->d_name)
> return treat_path_fast(dir, cdir, istate, path,
> - baselen, pathspec);
> + baselen, pathspec, cache);
> if (is_dot_or_dotdot(cdir->d_name) || !fspathcmp(cdir->d_name, ".git"))
> return path_none;
> strbuf_setlen(path, baselen);
> @@ -2348,7 +2363,7 @@ static enum path_treatment treat_path(struct dir_struct *dir,
> strbuf_addch(path, '/');
> return treat_directory(dir, istate, untracked,
> path->buf, path->len,
> - baselen, excluded, pathspec);
> + baselen, excluded, pathspec, cache);
> case DT_REG:
> case DT_LNK:
> if (pathspec &&
> @@ -2549,7 +2564,8 @@ static void add_path_to_appropriate_result_list(struct dir_struct *dir,
> static enum path_treatment read_directory_recursive(struct dir_struct *dir,
> struct index_state *istate, const char *base, int baselen,
> struct untracked_cache_dir *untracked, int check_only,
> - int stop_at_first_file, const struct pathspec *pathspec)
> + int stop_at_first_file, const struct pathspec *pathspec,
> + struct traversal_cache *cache)
> {
> /*
> * WARNING: Do NOT recurse unless path_recurse is returned from
> @@ -2572,7 +2588,7 @@ static enum path_treatment read_directory_recursive(struct dir_struct *dir,
> while (!read_cached_dir(&cdir)) {
> /* check how the file or directory should be treated */
> state = treat_path(dir, untracked, &cdir, istate, &path,
> - baselen, pathspec);
> + baselen, pathspec, cache);
> dir->visited_paths++;
>
> if (state > dir_state)
> @@ -2587,7 +2603,7 @@ static enum path_treatment read_directory_recursive(struct dir_struct *dir,
> subdir_state =
> read_directory_recursive(dir, istate, path.buf,
> path.len, ud,
> - check_only, stop_at_first_file, pathspec);
> + check_only, stop_at_first_file, pathspec, cache);
> if (subdir_state > dir_state)
> dir_state = subdir_state;
>
> @@ -2661,7 +2677,8 @@ int check_dir_entry_contains(const struct dir_entry *out, const struct dir_entry
> static int treat_leading_path(struct dir_struct *dir,
> struct index_state *istate,
> const char *path, int len,
> - const struct pathspec *pathspec)
> + const struct pathspec *pathspec,
> + struct traversal_cache *cache)
> {
> struct strbuf sb = STRBUF_INIT;
> struct strbuf subdir = STRBUF_INIT;
> @@ -2713,7 +2730,8 @@ static int treat_leading_path(struct dir_struct *dir,
> strbuf_reset(&subdir);
> strbuf_add(&subdir, path+prevlen, baselen-prevlen);
> cdir.d_name = subdir.buf;
> - state = treat_path(dir, NULL, &cdir, istate, &sb, prevlen, pathspec);
> +
> + state = treat_path(dir, NULL, &cdir, istate, &sb, prevlen, pathspec, cache);
>
> if (state != path_recurse)
> break; /* do not recurse into it */
> @@ -2986,6 +3004,9 @@ int read_directory(struct dir_struct *dir, struct index_state *istate,
> const char *path, int len, const struct pathspec *pathspec)
> {
> struct untracked_cache_dir *untracked;
> + struct traversal_cache cache = {
> + .real_gitdir = NULL,
> + };
>
> trace2_region_enter("dir", "read_directory", istate->repo);
> dir->visited_paths = 0;
> @@ -3003,8 +3024,10 @@ int read_directory(struct dir_struct *dir, struct index_state *istate,
> * e.g. prep_exclude()
> */
> dir->untracked = NULL;
> - if (!len || treat_leading_path(dir, istate, path, len, pathspec))
> - read_directory_recursive(dir, istate, path, len, untracked, 0, 0, pathspec);
> + if (!len || treat_leading_path(dir, istate, path, len, pathspec, &cache)) {
> + read_directory_recursive(dir, istate, path, len, untracked, 0, 0, pathspec, &cache);
> + }
> + FREE_AND_NULL(cache.real_gitdir);
> QSORT(dir->entries, dir->nr, cmp_dir_entry);
> QSORT(dir->ignored, dir->ignored_nr, cmp_dir_entry);
>
> --
> 2.36.0
This makes sense as a way to avoid the call to real_pathdup() if
that's what we want, but I feel it's a micro-optimization that isn't
worth this code churn. I'd rather drop this patch from the series and
just use the real_pathdup() you had before (see
https://lore.kernel.org/git/CABPp-BGXRzYCvyM38dEUvQ125+VtRu++7L9UiRz98u+1=Lov7A@xxxxxxxxxxxxxx/).
Let's see what Junio says, but I'm hoping he agrees this patch isn't
needed.
