analyze: generalize cat-config to apply to tmpfiles, presets, hwdb.d, etc.

Fixes #10256.

What works:

systemd-analyze cat-config systemd/system-preset
systemd-analyze cat-config systemd/user-preset
systemd-analyze cat-config tmpfiles.d
systemd-analyze cat-config sysusers.d
systemd-analyze cat-config systemd/sleep.conf
systemd-analyze cat-config systemd/user.conf
systemd-analyze cat-config systemd/system.conf
systemd-analyze cat-config udev/udev.conf
(and other .conf files)
systemd-analyze cat-config udev/rules.d
systemd-analyze cat-config environment.d
systemd-analyze cat-config environment

Directories may be specified with the trailing dash or not.

The caveat is that for user configuration, systemd and other tools also look
at ~/.config/. It would be nice to support this, but this patch doesn't.
"cat-config --user" is rejected, and we may allow it in the future and then
extend the search path with directories under ~/.config.

What doesn't work (and probably shouldn't because those files cannot be
meaningfully concatenated):

systemd-analyze cat-config systemd/system  (.service, .slice, .socket, ...)
systemd-analyze cat-config systemd/user
systemd-analyze cat-config systemd/network (.network, .link, and .dnssd)

The hardcoding of information about paths in this manner is a bit ugly, but
OTOH, it is not too onerous, and at least we have one place where all the
schemes are "documented" through code. It'll make us think twice before adding
yet another slightly different scheme.

src/analyze/analyze.c

@@ -2000,6 +2000,10 @@ static int parse_argv(int argc, char *argv[]) {
                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
                                        "Option --global only makes sense with verbs dot, unit-paths, verify.");
 
+        if (streq_ptr(argv[optind], "cat-config") && arg_scope == UNIT_FILE_USER)
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                       "Option --user is not supported for cat-config right now.");
+
         if (arg_root && !streq_ptr(argv[optind], "cat-config"))
                 return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
                                        "Option --root is only supported for cat-config right now.");

src/shared/pretty-print.c

@@ -213,33 +213,88 @@ void print_separator(void) {
                 fputs("\n\n", stdout);
 }
 
+static int guess_type(const char **name, bool *is_usr, bool *is_collection, const char **extension) {
+        /* Try to figure out if name is like tmpfiles.d/ or systemd/system-presets/,
+         * i.e. a collection of directories without a main config file. */
+
+        _cleanup_free_ char *n = NULL;
+        bool usr = false, coll = false;
+        const char *ext = ".conf";
+
+        if (path_equal(*name, "environment.d"))
+                /* Special case: we need to include /etc/environment in the search path, even
+                 * though the whole concept is called environment.d. */
+                *name = "environment";
+
+        n = strdup(*name);
+        if (!n)
+                return log_oom();
+
+        delete_trailing_chars(n, "/");
+
+        if (endswith(n, ".d"))
+                coll = true;
+
+        if (path_equal(n, "environment"))
+                usr = true;
+
+        if (path_equal(n, "udev/hwdb.d"))
+                ext = ".hwdb";
+
+        if (path_equal(n, "udev/rules.d"))
+                ext = ".rules";
+
+        if (PATH_IN_SET(n, "systemd/system-preset", "systemd/user-preset")) {
+                coll = true;
+                ext = ".preset";
+        }
+
+        if (path_equal(n, "systemd/user-preset"))
+                usr = true;
+
+        *is_usr = usr;
+        *is_collection = coll;
+        *extension = ext;
+        return 0;
+}
+
 int conf_files_cat(const char *root, const char *name) {
         _cleanup_strv_free_ char **dirs = NULL, **files = NULL;
         _cleanup_free_ char *path = NULL;
-        const char *dir;
+        char **dir;
+        bool is_usr, is_collection;
+        const char *extension;
         char **t;
         int r;
 
-        NULSTR_FOREACH(dir, CONF_PATHS_NULSTR("")) {
-                assert(endswith(dir, "/"));
-                r = strv_extendf(&dirs, "%s%s.d", dir, name);
+        r = guess_type(&name, &is_usr, &is_collection, &extension);
+        if (r < 0)
+                return r;
+
+        STRV_FOREACH(dir, is_usr ? CONF_PATHS_USR_STRV("") : CONF_PATHS_STRV("")) {
+                assert(endswith(*dir, "/"));
+                r = strv_extendf(&dirs, "%s%s%s", *dir, name,
+                                 is_collection ? "" : ".d");
                 if (r < 0)
                         return log_error_errno(r, "Failed to build directory list: %m");
         }
 
-        r = conf_files_list_strv(&files, ".conf", root, 0, (const char* const*) dirs);
+        r = conf_files_list_strv(&files, extension, root, 0, (const char* const*) dirs);
         if (r < 0)
                 return log_error_errno(r, "Failed to query file list: %m");
 
-        path = path_join(root, "/etc", name);
-        if (!path)
-                return log_oom();
+        if (!is_collection) {
+                path = path_join(root, "/etc", name);
+                if (!path)
+                        return log_oom();
+        }
 
         if (DEBUG_LOGGING) {
                 log_debug("Looking for configuration in:");
-                log_debug("   %s", path);
+                if (path)
+                        log_debug("   %s", path);
                 STRV_FOREACH(t, dirs)
-                        log_debug("   %s/*.conf", *t);
+                        log_debug("   %s/*%s", *t, extension);
         }
 
         /* show */