tmpfiles: add --cat-config

This implements similar logic as conf_files_cat(), but with slightly different
file gathering logic. I also want to add support for replacement files later on,
so it seems better to keep those two file-gathering functions separate.

man/standard-options.xml

@@ -50,4 +50,13 @@
       footer with hints.</para>
     </listitem>
   </varlistentry>
+
+  <varlistentry id='cat-config'>
+    <term><option>--cat-config</option></term>
+
+    <listitem>
+      <para>Copy the contents of config files to standard output.
+      Before each file, the filename is printed as a comment.</para>
+    </listitem>
+  </varlistentry>
 </variablelist>

man/systemd-tmpfiles.xml

@@ -183,6 +183,7 @@
         </para></listitem>
       </varlistentry>
 
+      <xi:include href="standard-options.xml" xpointer="cat-config" />
       <xi:include href="standard-options.xml" xpointer="help" />
       <xi:include href="standard-options.xml" xpointer="version" />
     </variablelist>

src/basic/conf-files.c

@@ -259,6 +259,41 @@ int conf_files_list_nulstr(char ***strv, const char *suffix, const char *root, u
         return conf_files_list_strv_internal(strv, suffix, root, flags, d);
 }
 
+int conf_files_list_with_replacement(
+                const char *root,
+                char **config_dirs,
+                const char *replacement,
+                char ***files,
+                char **replace_file) {
+
+        _cleanup_strv_free_ char **f = NULL;
+        _cleanup_free_ char *p = NULL;
+        int r;
+
+        assert(config_dirs);
+        assert(files);
+        assert(replace_file || !replacement);
+
+        r = conf_files_list_strv(&f, ".conf", root, 0, (const char* const*) config_dirs);
+        if (r < 0)
+                return log_error_errno(r, "Failed to enumerate config files: %m");
+
+        if (replacement) {
+                r = conf_files_insert(&f, root, config_dirs, replacement);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to extend config file list: %m");
+
+                p = path_join(root, replacement, NULL);
+                if (!p)
+                        return log_oom();
+        }
+
+        *files = TAKE_PTR(f);
+        if (replace_file)
+                *replace_file = TAKE_PTR(p);
+        return 0;
+}
+
 int conf_files_cat(const char *name) {
         _cleanup_strv_free_ char **dirs = NULL, **files = NULL;
         const char *dir;

src/basic/conf-files.h

@@ -17,4 +17,10 @@ int conf_files_list_strv(char ***ret, const char *suffix, const char *root, unsi
 int conf_files_list_nulstr(char ***ret, const char *suffix, const char *root, unsigned flags, const char *dirs);
 int conf_files_insert(char ***strv, const char *root, char **dirs, const char *path);
 int conf_files_insert_nulstr(char ***strv, const char *root, const char *dirs, const char *path);
+int conf_files_list_with_replacement(
+                const char *root,
+                char **config_dirs,
+                const char *replacement,
+                char ***files,
+                char **replace_file);
 int conf_files_cat(const char *name);

src/tmpfiles/tmpfiles.c

@@ -60,6 +60,7 @@
 #include "string-table.h"
 #include "string-util.h"
 #include "strv.h"
+#include "terminal-util.h"
 #include "umask-util.h"
 #include "user-util.h"
 #include "util.h"
@@ -149,6 +150,7 @@ typedef enum DirectoryType {
         _DIRECTORY_TYPE_MAX,
 } DirectoryType;
 
+static bool arg_cat_config = false;
 static bool arg_user = false;
 static bool arg_create = false;
 static bool arg_clean = false;
@@ -2441,12 +2443,24 @@ static int parse_line(const char *fname, unsigned line, const char *buffer, bool
         return 0;
 }
 
+static int cat_config(char **config_dirs, char **args) {
+        _cleanup_strv_free_ char **files = NULL;
+        int r;
+
+        r = conf_files_list_with_replacement(arg_root, config_dirs, arg_replace, &files, NULL);
+        if (r < 0)
+                return r;
+
+        return cat_files(NULL, files, 0);
+}
+
 static void help(void) {
         printf("%s [OPTIONS...] [CONFIGURATION FILE...]\n\n"
                "Creates, deletes and cleans up volatile and temporary files and directories.\n\n"
                "  -h --help                 Show this help\n"
                "     --user                 Execute user configuration\n"
                "     --version              Show package version\n"
+               "     --cat-config           Show configuration files\n"
                "     --create               Create marked files/directories\n"
                "     --clean                Clean up marked directories\n"
                "     --remove               Remove marked files/directories\n"
@@ -2462,6 +2476,7 @@ static int parse_argv(int argc, char *argv[]) {
 
         enum {
                 ARG_VERSION = 0x100,
+                ARG_CAT_CONFIG,
                 ARG_USER,
                 ARG_CREATE,
                 ARG_CLEAN,
@@ -2477,6 +2492,7 @@ static int parse_argv(int argc, char *argv[]) {
                 { "help",           no_argument,         NULL, 'h'                },
                 { "user",           no_argument,         NULL, ARG_USER           },
                 { "version",        no_argument,         NULL, ARG_VERSION        },
+                { "cat-config",     no_argument,         NULL, ARG_CAT_CONFIG     },
                 { "create",         no_argument,         NULL, ARG_CREATE         },
                 { "clean",          no_argument,         NULL, ARG_CLEAN          },
                 { "remove",         no_argument,         NULL, ARG_REMOVE         },
@@ -2504,6 +2520,10 @@ static int parse_argv(int argc, char *argv[]) {
                 case ARG_VERSION:
                         return version();
 
+                case ARG_CAT_CONFIG:
+                        arg_cat_config = true;
+                        break;
+
                 case ARG_USER:
                         arg_user = true;
                         break;
@@ -2557,11 +2577,16 @@ static int parse_argv(int argc, char *argv[]) {
                         assert_not_reached("Unhandled option");
                 }
 
-        if (!arg_clean && !arg_create && !arg_remove) {
+        if (!arg_clean && !arg_create && !arg_remove && !arg_cat_config) {
                 log_error("You need to specify at least one of --clean, --create or --remove.");
                 return -EINVAL;
         }
 
+        if (arg_replace && arg_cat_config) {
+                log_error("Option --replace= is not supported with --cat-config");
+                return -EINVAL;
+        }
+
         if (arg_replace && optind >= argc) {
                 log_error("When --replace= is given, some configuration items must be specified");
                 return -EINVAL;
@@ -2677,19 +2702,9 @@ static int read_config_files(char **config_dirs, char **args, bool *invalid_conf
         char **f;
         int r;
 
-        r = conf_files_list_strv(&files, ".conf", arg_root, 0, (const char* const*) config_dirs);
+        r = conf_files_list_with_replacement(arg_root, config_dirs, arg_replace, &files, &p);
         if (r < 0)
-                return log_error_errno(r, "Failed to enumerate tmpfiles.d files: %m");
-
-        if (arg_replace) {
-                r = conf_files_insert(&files, arg_root, config_dirs, arg_replace);
-                if (r < 0)
-                        return log_error_errno(r, "Failed to extend tmpfiles.d file list: %m");
-
-                p = path_join(arg_root, arg_replace, NULL);
-                if (!p)
-                        return log_oom();
-        }
+                return r;
 
         STRV_FOREACH(f, files)
                 if (p && path_equal(*f, p)) {
@@ -2721,20 +2736,6 @@ int main(int argc, char *argv[]) {
         log_parse_environment();
         log_open();
 
-        umask(0022);
-
-        mac_selinux_init();
-
-        items = ordered_hashmap_new(&string_hash_ops);
-        globs = ordered_hashmap_new(&string_hash_ops);
-
-        if (!items || !globs) {
-                r = log_oom();
-                goto finish;
-        }
-
-        r = 0;
-
         if (arg_user) {
                 r = user_config_paths(&config_dirs);
                 if (r < 0) {
@@ -2757,6 +2758,23 @@ int main(int argc, char *argv[]) {
                         log_debug("Looking for configuration files in (higher priority first):\n\t%s", t);
         }
 
+        if (arg_cat_config) {
+                r = cat_config(config_dirs, argv + optind);
+                goto finish;
+        }
+
+        umask(0022);
+
+        mac_selinux_init();
+
+        items = ordered_hashmap_new(&string_hash_ops);
+        globs = ordered_hashmap_new(&string_hash_ops);
+
+        if (!items || !globs) {
+                r = log_oom();
+                goto finish;
+        }
+
         /* If command line arguments are specified along with --replace, read all
          * configuration files and insert the positional arguments at the specified
          * place. Otherwise, if command line arguments are specified, execute just