fs-util: unify code we use to check if dirent's d_name is "." or ".."

We use different idioms at different places. Let's replace this is the
one true new idiom, that is even a bit faster...

src/basic/cgroup-util.c

@@ -182,8 +182,7 @@ int cg_read_subgroup(DIR *d, char **fn) {
                 if (de->d_type != DT_DIR)
                         continue;
 
-                if (streq(de->d_name, ".") ||
+                if (dot_or_dot_dot(de->d_name))
-                    streq(de->d_name, ".."))
                         continue;
 
                 b = strdup(de->d_name);

src/basic/copy.c

@@ -331,7 +331,7 @@ static int fd_copy_directory(
                 struct stat buf;
                 int q;
 
-                if (STR_IN_SET(de->d_name, ".", ".."))
+                if (dot_or_dot_dot(de->d_name))
                         continue;
 
                 if (fstatat(dirfd(d), de->d_name, &buf, AT_SYMLINK_NOFOLLOW) < 0) {

src/basic/path-util.c

@@ -699,10 +699,7 @@ bool filename_is_valid(const char *p) {
         if (isempty(p))
                 return false;
 
-        if (streq(p, "."))
+        if (dot_or_dot_dot(p))
-                return false;
-
-        if (streq(p, ".."))
                 return false;
 
         e = strchrnul(p, '/');
@@ -720,14 +717,17 @@ bool path_is_safe(const char *p) {
         if (isempty(p))
                 return false;
 
-        if (streq(p, "..") || startswith(p, "../") || endswith(p, "/..") || strstr(p, "/../"))
+        if (dot_or_dot_dot(p))
+                return false;
+
+        if (startswith(p, "../") || endswith(p, "/..") || strstr(p, "/../"))
                 return false;
 
         if (strlen(p)+1 > PATH_MAX)
                 return false;
 
         /* The following two checks are not really dangerous, but hey, they still are confusing */
-        if (streq(p, ".") || startswith(p, "./") || endswith(p, "/.") || strstr(p, "/./"))
+        if (startswith(p, "./") || endswith(p, "/.") || strstr(p, "/./"))
                 return false;
 
         if (strstr(p, "//"))
@@ -892,3 +892,16 @@ int systemd_installation_has_version(const char *root, unsigned minimal_version)
 
         return false;
 }
+
+bool dot_or_dot_dot(const char *path) {
+        if (!path)
+                return false;
+        if (path[0] != '.')
+                return false;
+        if (path[1] == 0)
+                return true;
+        if (path[1] != '.')
+                return false;
+
+        return path[2] == 0;
+}

src/basic/path-util.h

@@ -141,3 +141,5 @@ bool is_device_path(const char *path);
 bool is_deviceallow_pattern(const char *path);
 
 int systemd_installation_has_version(const char *root, unsigned minimal_version);
+
+bool dot_or_dot_dot(const char *path);

src/basic/rm-rf.c

@@ -83,7 +83,7 @@ int rm_rf_children(int fd, RemoveFlags flags, struct stat *root_dev) {
                 bool is_dir;
                 struct stat st;
 
-                if (streq(de->d_name, ".") || streq(de->d_name, ".."))
+                if (dot_or_dot_dot(de->d_name))
                         continue;
 
                 if (de->d_type == DT_UNKNOWN ||

src/basic/socket-util.c

@@ -877,7 +877,7 @@ bool ifname_valid(const char *p) {
         if (strlen(p) >= IFNAMSIZ)
                 return false;
 
-        if (STR_IN_SET(p, ".", ".."))
+        if (dot_or_dot_dot(p))
                 return false;
 
         while (*p) {

src/gpt-auto-generator/gpt-auto-generator.c

@@ -658,7 +658,7 @@ static int get_block_device_harder(const char *path, dev_t *dev) {
 
         FOREACH_DIRENT_ALL(de, d, return -errno) {
 
-                if (STR_IN_SET(de->d_name, ".", ".."))
+                if (dot_or_dot_dot(de->d_name))
                         continue;
 
                 if (!IN_SET(de->d_type, DT_LNK, DT_UNKNOWN))

src/nspawn/nspawn-patch-uid.c

@@ -375,7 +375,7 @@ static int recurse_fd(int fd, bool donate_fd, const struct stat *st, uid_t shift
                 FOREACH_DIRENT_ALL(de, d, r = -errno; goto finish) {
                         struct stat fst;
 
-                        if (STR_IN_SET(de->d_name, ".", ".."))
+                        if (dot_or_dot_dot(de->d_name))
                                 continue;
 
                         if (fstatat(dirfd(d), de->d_name, &fst, AT_SYMLINK_NOFOLLOW) < 0) {

src/resolve/resolved-manager.c

@@ -1349,7 +1349,7 @@ void manager_cleanup_saved_user(Manager *m) {
                 if (!IN_SET(de->d_type, DT_UNKNOWN, DT_REG))
                         continue;
 
-                if (STR_IN_SET(de->d_name, ".", ".."))
+                if (dot_or_dot_dot(de->d_name))
                         continue;
 
                 r = parse_ifindex(de->d_name, &ifindex);

src/shared/clean-ipc.c

@@ -225,7 +225,7 @@ static int clean_posix_shm_internal(DIR *dir, uid_t uid, gid_t gid) {
         FOREACH_DIRENT_ALL(de, dir, goto fail) {
                 struct stat st;
 
-                if (STR_IN_SET(de->d_name, "..", "."))
+                if (dot_or_dot_dot(de->d_name))
                         continue;
 
                 if (fstatat(dirfd(dir), de->d_name, &st, AT_SYMLINK_NOFOLLOW) < 0) {
@@ -310,7 +310,7 @@ static int clean_posix_mq(uid_t uid, gid_t gid) {
                 struct stat st;
                 char fn[1+strlen(de->d_name)+1];
 
-                if (STR_IN_SET(de->d_name, "..", "."))
+                if (dot_or_dot_dot(de->d_name))
                         continue;
 
                 if (fstatat(dirfd(dir), de->d_name, &st, AT_SYMLINK_NOFOLLOW) < 0) {

src/test/test-fs-util.c

@@ -305,12 +305,23 @@ static void test_var_tmp(void) {
         }
 }
 
+static void test_dot_or_dot_dot(void) {
+        assert_se(!dot_or_dot_dot(NULL));
+        assert_se(!dot_or_dot_dot(""));
+        assert_se(!dot_or_dot_dot("xxx"));
+        assert_se(dot_or_dot_dot("."));
+        assert_se(dot_or_dot_dot(".."));
+        assert_se(!dot_or_dot_dot(".foo"));
+        assert_se(!dot_or_dot_dot("..foo"));
+}
+
 int main(int argc, char *argv[]) {
         test_unlink_noerrno();
         test_readlink_and_make_absolute();
         test_get_files_in_directory();
         test_var_tmp();
         test_chase_symlinks();
+        test_dot_or_dot_dot();
 
         return 0;
 }

src/tmpfiles/tmpfiles.c

@@ -385,7 +385,7 @@ static int dir_cleanup(
                 usec_t age;
                 _cleanup_free_ char *sub_path = NULL;
 
-                if (STR_IN_SET(dent->d_name, ".", ".."))
+                if (dot_or_dot_dot(dent->d_name))
                         continue;
 
                 if (fstatat(dirfd(d), dent->d_name, &s, AT_SYMLINK_NOFOLLOW) < 0) {
@@ -1070,9 +1070,7 @@ static int item_do_children(Item *i, const char *path, action_t action) {
                 _cleanup_free_ char *p = NULL;
                 int q;
 
-                errno = 0;
+                if (dot_or_dot_dot(de->d_name))
-
-                if (STR_IN_SET(de->d_name, ".", ".."))
                         continue;
 
                 p = strjoin(path, "/", de->d_name);