Kjetil Barvik <barvik@xxxxxxxxxxxx> writes: > +static inline void > +update_path_cache(unsigned int ret_flags, unsigned int track_flags, > + int last_slash) > +{ > + /* Max 3 different path types can be cached for the moment! */ > + unsigned int save_flags = > + ret_flags & track_flags & (LSTAT_DIR| > + LSTAT_NOTDIR| > + LSTAT_SYMLINK); > + if (save_flags && last_slash > 0 && last_slash < PATH_MAX) { > + cache_flags = save_flags; > + cache_len = last_slash; > + } else { > + cache_flags = 0; > + cache_len = 0; > + } > +} I personally found this inline function with a single call site distracting in following the logic. It does not make the indentation level shallower, either. Also, the else part should probably call clear_lstat_cache() to protect it from possible future enhancements to add more state variables. > + > +/* > + * Check if name 'name' of length 'len' has a symlink leading > + * component, or if the directory exists and is real, or not. > + * > + * To speed up the check, some information is allowed to be cached. > + * This is indicated by the 'track_flags' argument. > + */ > +unsigned int > +check_lstat_cache(int len, const char *name, unsigned int track_flags) > +{ > + int match_len, last_slash, max_len; > + unsigned int match_flags, ret_flags; > + struct stat st; > + > + /* Check if match from the cache for 2 "excluding" path types. > + */ > + match_len = last_slash = > + greatest_common_path_cache_prefix(len, name); > + match_flags = > + cache_flags & track_flags & (LSTAT_NOTDIR| > + LSTAT_SYMLINK); > + if (match_flags && match_len == cache_len) > + return match_flags; Let me see if I understand the logic behind this caching. When you have checked A/B/C earlier and you already know B is a symlink, you remember that A/B was a symlink.. You can fill a request to check A/B/$whatever (assuming A/B does not change --- otherwise the caller should clear the cache) from the cached data, because no matter what $whatever is, it will result in the same "has-leading-symlink". Similarly, if you know A/B is not a directory from an earlier test, you know that a request to check A/B/$whatever will result in the same ENOTDIR no matter what $whatever is, so you can return early. The above "return match_flags" will not trigger if the cached path does not have any leading symlink. So we know the matched part are all good directories when we start lstat() loop. Am I following you so far? > + /* Okay, no match from the cache so far, so now we have to > + * check the rest of the path components and update the cache. > + */ > + ret_flags = LSTAT_DIR; > + max_len = len < PATH_MAX ? len : PATH_MAX; > + while (match_len < max_len) { > + do { > + cache_path[match_len] = name[match_len]; > + match_len++; > + } while (match_len < max_len && name[match_len] != '/'); You take one component from the input, and append it to the part that is already known to be true directory (i.e. cached part and the part earlier iteration of the loop checked so far), to be tested by lstat()... > + if (match_len >= max_len) > + break; ... but you are not interested in the full input. We are only checking the leading path (e.g. check for "A/B/C" may lstat() "A", "A/B" but not "A/B/C"). > + last_slash = match_len; > + cache_path[last_slash] = '\0'; > + > + if (lstat(cache_path, &st)) { > + ret_flags = LSTAT_LSTATERR; > + if (errno == ENOENT || errno == ENOTDIR) > + ret_flags |= LSTAT_NOTDIR; If you tested "A/B" here and got ENOENT back, you know "A/B" does not exist; you cache this knowledge as "A/B is not a directory" (I also think you could use it as a cached knowledge that "A exists and is a directory". I am not sure if you are taking advantage of that). What I do not understand about this code is the ENOTDIR case. If you tested "A/B" and got ENOTDIR back, what you know is that "A" is not a directory (if the path tested this round were deeper like "X/Y/A/B", you know "X/Y/A" is not a directory, and you know "X" and "X/Y" are true directories; otherwise the loop would have exited before this round when you tested "X" or "X/Y" in the earlier rounds). So as far as I can think of, ENOENT case and ENOTDIR case would give you different information (ENOENT would say "A is a dir, A/B is not"; ENOTDIR would say "A is not a dir"). I am confused how you can cache the same path and same flag between these two cases here. > + } else if (S_ISDIR(st.st_mode)) { > + continue; > + } else if (S_ISLNK(st.st_mode)) { > + ret_flags = LSTAT_SYMLINK; > + } else { > + ret_flags = LSTAT_ERR; > + } > + break; > + } > + update_path_cache(ret_flags, track_flags, last_slash); > + return ret_flags; > +} > + > +/* > + * Before usage of the check_lstat_cache() function one should call > + * clear_lstat_cache() (at an appropriate place) to make sure that the > + * cache is clean before first call to check_lstat_cache(). > + */ > +void clear_lstat_cache(void) > +{ > + cache_flags = 0; > + cache_len = 0; > +} > -- > 1.6.1.rc1.49.g7f705 -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html