diff options
Diffstat (limited to 'symlinks.c')
| -rw-r--r-- | symlinks.c | 241 |
1 files changed, 241 insertions, 0 deletions
diff --git a/symlinks.c b/symlinks.c new file mode 100644 index 0000000000..f262b7c44b --- /dev/null +++ b/symlinks.c @@ -0,0 +1,241 @@ +#include "cache.h" + +static struct cache_def { + char path[PATH_MAX + 1]; + int len; + int flags; + int track_flags; + int prefix_len_stat_func; +} cache; + +/* + * Returns the length (on a path component basis) of the longest + * common prefix match of 'name' and the cached path string. + */ +static inline int longest_match_lstat_cache(int len, const char *name, + int *previous_slash) +{ + int max_len, match_len = 0, match_len_prev = 0, i = 0; + + max_len = len < cache.len ? len : cache.len; + while (i < max_len && name[i] == cache.path[i]) { + if (name[i] == '/') { + match_len_prev = match_len; + match_len = i; + } + i++; + } + /* Is the cached path string a substring of 'name'? */ + if (i == cache.len && cache.len < len && name[cache.len] == '/') { + match_len_prev = match_len; + match_len = cache.len; + /* Is 'name' a substring of the cached path string? */ + } else if ((i == len && len < cache.len && cache.path[len] == '/') || + (i == len && len == cache.len)) { + match_len_prev = match_len; + match_len = len; + } + *previous_slash = match_len_prev; + return match_len; +} + +static inline void reset_lstat_cache(int track_flags, int prefix_len_stat_func) +{ + cache.path[0] = '\0'; + cache.len = 0; + cache.flags = 0; + cache.track_flags = track_flags; + cache.prefix_len_stat_func = prefix_len_stat_func; +} + +#define FL_DIR (1 << 0) +#define FL_NOENT (1 << 1) +#define FL_SYMLINK (1 << 2) +#define FL_LSTATERR (1 << 3) +#define FL_ERR (1 << 4) +#define FL_FULLPATH (1 << 5) + +/* + * 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 can be indicated by the 'track_flags' argument, which also can + * be used to indicate that we should check the full path. + * + * The 'prefix_len_stat_func' parameter can be used to set the length + * of the prefix, where the cache should use the stat() function + * instead of the lstat() function to test each path component. + */ +static int lstat_cache(int len, const char *name, + int track_flags, int prefix_len_stat_func) +{ + int match_len, last_slash, last_slash_dir, previous_slash; + int match_flags, ret_flags, save_flags, max_len, ret; + struct stat st; + + if (cache.track_flags != track_flags || + cache.prefix_len_stat_func != prefix_len_stat_func) { + /* + * As a safeguard we clear the cache if the values of + * track_flags and/or prefix_len_stat_func does not + * match with the last supplied values. + */ + reset_lstat_cache(track_flags, prefix_len_stat_func); + match_len = last_slash = 0; + } else { + /* + * Check to see if we have a match from the cache for + * the 2 "excluding" path types. + */ + match_len = last_slash = + longest_match_lstat_cache(len, name, &previous_slash); + match_flags = cache.flags & track_flags & (FL_NOENT|FL_SYMLINK); + if (match_flags && match_len == cache.len) + return match_flags; + /* + * If we now have match_len > 0, we would know that + * the matched part will always be a directory. + * + * Also, if we are tracking directories and 'name' is + * a substring of the cache on a path component basis, + * we can return immediately. + */ + match_flags = track_flags & FL_DIR; + if (match_flags && len == match_len) + return match_flags; + } + + /* + * Okay, no match from the cache so far, so now we have to + * check the rest of the path components. + */ + ret_flags = FL_DIR; + last_slash_dir = last_slash; + 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] != '/'); + if (match_len >= max_len && !(track_flags & FL_FULLPATH)) + break; + last_slash = match_len; + cache.path[last_slash] = '\0'; + + if (last_slash <= prefix_len_stat_func) + ret = stat(cache.path, &st); + else + ret = lstat(cache.path, &st); + + if (ret) { + ret_flags = FL_LSTATERR; + if (errno == ENOENT) + ret_flags |= FL_NOENT; + } else if (S_ISDIR(st.st_mode)) { + last_slash_dir = last_slash; + continue; + } else if (S_ISLNK(st.st_mode)) { + ret_flags = FL_SYMLINK; + } else { + ret_flags = FL_ERR; + } + break; + } + + /* + * At the end update the cache. Note that max 3 different + * path types, FL_NOENT, FL_SYMLINK and FL_DIR, can be cached + * for the moment! + */ + save_flags = ret_flags & track_flags & (FL_NOENT|FL_SYMLINK); + if (save_flags && last_slash > 0 && last_slash <= PATH_MAX) { + cache.path[last_slash] = '\0'; + cache.len = last_slash; + cache.flags = save_flags; + } else if (track_flags & FL_DIR && + last_slash_dir > 0 && last_slash_dir <= PATH_MAX) { + /* + * We have a separate test for the directory case, + * since it could be that we have found a symlink or a + * non-existing directory and the track_flags says + * that we cannot cache this fact, so the cache would + * then have been left empty in this case. + * + * But if we are allowed to track real directories, we + * can still cache the path components before the last + * one (the found symlink or non-existing component). + */ + cache.path[last_slash_dir] = '\0'; + cache.len = last_slash_dir; + cache.flags = FL_DIR; + } else { + reset_lstat_cache(track_flags, prefix_len_stat_func); + } + return ret_flags; +} + +/* + * Invalidate the given 'name' from the cache, if 'name' matches + * completely with the cache. + */ +void invalidate_lstat_cache(int len, const char *name) +{ + int match_len, previous_slash; + + match_len = longest_match_lstat_cache(len, name, &previous_slash); + if (len == match_len) { + if ((cache.track_flags & FL_DIR) && previous_slash > 0) { + cache.path[previous_slash] = '\0'; + cache.len = previous_slash; + cache.flags = FL_DIR; + } else + reset_lstat_cache(cache.track_flags, + cache.prefix_len_stat_func); + } +} + +/* + * Completely clear the contents of the cache + */ +void clear_lstat_cache(void) +{ + reset_lstat_cache(0, 0); +} + +#define USE_ONLY_LSTAT 0 + +/* + * Return non-zero if path 'name' has a leading symlink component + */ +int has_symlink_leading_path(int len, const char *name) +{ + return lstat_cache(len, name, + FL_SYMLINK|FL_DIR, USE_ONLY_LSTAT) & + FL_SYMLINK; +} + +/* + * Return non-zero if path 'name' has a leading symlink component or + * if some leading path component does not exists. + */ +int has_symlink_or_noent_leading_path(int len, const char *name) +{ + return lstat_cache(len, name, + FL_SYMLINK|FL_NOENT|FL_DIR, USE_ONLY_LSTAT) & + (FL_SYMLINK|FL_NOENT); +} + +/* + * Return non-zero if all path components of 'name' exists as a + * directory. If prefix_len > 0, we will test with the stat() + * function instead of the lstat() function for a prefix length of + * 'prefix_len', thus we then allow for symlinks in the prefix part as + * long as those points to real existing directories. + */ +int has_dirs_only_path(int len, const char *name, int prefix_len) +{ + return lstat_cache(len, name, + FL_DIR|FL_FULLPATH, prefix_len) & + FL_DIR; +} |