Add support for creating utmp records

This patch adds support for creating utmp records using the ‘utempter’
helper binary from the ‘libutempter’ package.

* New config option ‘main.utempter’
* New meson command line option, -Ddefault-utempter-path. Defaults to
  auto-detecting the path.

The default value of the new ‘main.utempter’ config option depends on
the meson command line option ‘-Ddefault-utempter-path’.

If ‘main.utempter’ is *not* set to ‘none’, foot will try to execute
the utempter helper binary to create utmp records when a new terminal
is instantiated. The record is removed when the terminal instance is
destroyed.

CHANGELOG.md

@@ -46,6 +46,8 @@
 ### Added
 
 * Support for adjusting the thickness of regular underlines ([#1136][1136]).
+* Support (optional) for utmp logging with libutempter.
+
 
 [1136]: https://codeberg.org/dnkl/foot/issues/1136
 

INSTALL.md

@@ -45,6 +45,7 @@ subprojects.
 * wayland (_client_ and _cursor_ libraries)
 * xkbcommon
 * utf8proc (_optional_, needed for grapheme clustering)
+* libutempter (_optional_, needed for utmp logging)
 * [fcft](https://codeberg.org/dnkl/fcft) [^1]
 
 [^1]: can also be built as subprojects, in which case they are
@@ -141,16 +142,17 @@ mkdir -p bld/release && cd bld/release
 
 Available compile-time options:
 
-| Option                               | Type    | Default                 | Description                                           | Extra dependencies |
+| Option                               | Type    | Default                 | Description                                               | Extra dependencies |
-|--------------------------------------|---------|-------------------------|-------------------------------------------------------|--------------------|
+|--------------------------------------|---------|-------------------------|-----------------------------------------------------------|--------------------|
-| `-Ddocs`                             | feature | `auto`                  | Builds and install documentation                      | scdoc              |
+| `-Ddocs`                             | feature | `auto`                  | Builds and install documentation                          | scdoc              |
-| `-Dtests`                            | bool    | `true`                  | Build tests (adds a `ninja test` build target)        | none               |
+| `-Dtests`                            | bool    | `true`                  | Build tests (adds a `ninja test` build target)            | none               |
-| `-Dime`                              | bool    | `true`                  | Enables IME support                                   | None               |
+| `-Dime`                              | bool    | `true`                  | Enables IME support                                       | None               |
-| `-Dgrapheme-clustering`              | feature | `auto`                  | Enables grapheme clustering                           | libutf8proc        |
+| `-Dgrapheme-clustering`              | feature | `auto`                  | Enables grapheme clustering                               | libutf8proc        |
-| `-Dterminfo`                         | feature | `enabled`               | Build and install terminfo files                      | tic (ncurses)      |
+| `-Dterminfo`                         | feature | `enabled`               | Build and install terminfo files                          | tic (ncurses)      |
-| `-Ddefault-terminfo`                 | string  | `foot`                  | Default value of `TERM`                               | none               |
+| `-Ddefault-terminfo`                 | string  | `foot`                  | Default value of `TERM`                                   | none               |
-| `-Dcustom-terminfo-install-location` | string  | `${datadir}/terminfo`   | Value to set `TERMINFO` to                            | None               |
+| `-Dcustom-terminfo-install-location` | string  | `${datadir}/terminfo`   | Value to set `TERMINFO` to                                | None               |
-| `-Dsystemd-units-dir`                | string  | `${systemduserunitdir}` | Where to install the systemd service files (absolute) | None               |
+| `-Dsystemd-units-dir`                | string  | `${systemduserunitdir}` | Where to install the systemd service files (absolute)     | None               |
+| `-Ddefault-utempter-path`            | feature | `auto`                  | Default path to utempter binary (‘none’ disables default) | libutempter        |
 
 Documentation includes the man pages, readme, changelog and license
 files.

config.c

@@ -944,6 +944,18 @@ parse_section_main(struct context *ctx)
     else if (strcmp(key, "box-drawings-uses-font-glyphs") == 0)
         return value_to_bool(ctx, &conf->box_drawings_uses_font_glyphs);
 
+    else if (strcmp(key, "utempter") == 0) {
+        if (!value_to_str(ctx, &conf->utempter_path))
+            return false;
+
+        if (strcmp(conf->utempter_path, "none") == 0) {
+            free(conf->utempter_path);
+            conf->utempter_path = NULL;
+        }
+
+        return true;
+    }
+
     else {
         LOG_CONTEXTUAL_ERR("not a valid option: %s", key);
         return false;
@@ -2937,6 +2949,9 @@ config_load(struct config *conf, const char *conf_path,
         },
 
         .env_vars = tll_init(),
+        .utempter_path = (strlen(FOOT_DEFAULT_UTEMPTER_PATH) > 0
+                          ? xstrdup(FOOT_DEFAULT_UTEMPTER_PATH)
+                          : NULL),
         .notifications = tll_init(),
     };
 
@@ -3225,6 +3240,9 @@ config_clone(const struct config *old)
         tll_push_back(conf->env_vars, copy);
     }
 
+    conf->utempter_path =
+        old->utempter_path != NULL ? xstrdup(old->utempter_path) : NULL;
+
     conf->notifications.length = 0;
     conf->notifications.head = conf->notifications.tail = 0;
     tll_foreach(old->notifications, it) {
@@ -3291,6 +3309,7 @@ config_free(struct config *conf)
         tll_remove(conf->env_vars, it);
     }
 
+    free(conf->utempter_path);
     user_notifications_free(&conf->notifications);
 }
 

config.h

@@ -319,6 +319,8 @@ struct config {
 
     env_var_list_t env_vars;
 
+    char *utempter_path;
+
     struct {
         enum fcft_scaling_filter fcft_filter;
         bool overflowing_glyphs;

doc/foot.ini.5.scd

@@ -317,6 +317,10 @@ commented out will usually be installed to */etc/xdg/foot/foot.ini*.
 	(including SMT). Note that this is not always the best value. In
 	some cases, the number of physical _cores_ is better.
 
+*utempter*
+	Path to utempter helper binary. Set to *none* to disable utmp
+	records. Default: _@utempter@_.
+
 # SECTION: environment
 
 This section is used to define environment variables that will be set

doc/meson.build

@@ -2,9 +2,16 @@ sh = find_program('sh', native: true)
 
 scdoc_prog = find_program(scdoc.get_variable('scdoc'), native: true)
 
+if utempter_path == ''
+  default_utempter_value = 'not set'
+else
+  default_utempter_value = utempter_path
+endif
+
 conf_data = configuration_data(
   {
     'default_terminfo': get_option('default-terminfo'),
+    'utempter': default_utempter_value,
   }
 )
 

foot.ini

@@ -33,6 +33,7 @@
 # word-delimiters=,│`|:"'()[]{}<>
 # selection-target=primary
 # workers=<number of logical CPUs>
+# utempter=/usr/lib/utempter/utempter
 
 [environment]
 # name=value

meson.build

@@ -16,9 +16,30 @@ if cc.has_function('memfd_create')
   add_project_arguments('-DMEMFD_CREATE', language: 'c')
 endif
 
+utempter_path = get_option('default-utempter-path')
+if utempter_path == ''
+  utempter = find_program(
+    'utempter',
+    required: false,
+    dirs: [join_paths(get_option('prefix'), get_option('libdir'), 'utempter'),
+           join_paths(get_option('prefix'), get_option('libexecdir'), 'utempter'),
+           '/usr/lib/utempter',
+           '/usr/libexec/utempter',
+           '/lib/utempter']
+  )
+  if utempter.found()
+    utempter_path = utempter.full_path()
+  else
+    utempter_path = ''
+  endif
+elif utempter_path == 'none'
+  utempter_path = ''
+endif
+
 add_project_arguments(
   ['-D_GNU_SOURCE=200809L',
-   '-DFOOT_DEFAULT_TERM="@0@"'.format(get_option('default-terminfo'))] +
+   '-DFOOT_DEFAULT_TERM="@0@"'.format(get_option('default-terminfo')),
+   '-DFOOT_DEFAULT_UTEMPTER_PATH="@0@"'.format(utempter_path)] +
   (is_debug_build
     ? ['-D_DEBUG']
    : [cc.get_supported_arguments('-fno-asynchronous-unwind-tables')]) +
@@ -321,6 +342,7 @@ summary(
     'Themes': get_option('themes'),
     'IME': get_option('ime'),
     'Grapheme clustering': utf8proc.found(),
+    'Utempter path': utempter_path,
     'Build terminfo': tic.found(),
     'Terminfo install location': terminfo_install_location,
     'Default TERM': get_option('default-terminfo'),

meson_options.txt

@@ -21,3 +21,6 @@ option('custom-terminfo-install-location', type: 'string', value: '',
 
 option('systemd-units-dir', type: 'string', value: '',
       description: 'Where to install the systemd service files (absolute path). Default: ${systemduserunitdir}')
+
+option('default-utempter-path', type: 'string', value: '',
+       description: 'Default path to utempter helper binary. Default: auto-detect')

terminal.c

@@ -203,6 +203,30 @@ fdm_ptmx_out(struct fdm *fdm, int fd, int events, void *data)
     return true;
 }
 
+static bool
+add_utmp_record(const struct config *conf, struct reaper *reaper, int ptmx)
+{
+    if (ptmx < 0)
+        return true;
+    if (conf->utempter_path == NULL)
+        return true;
+
+    char *const argv[] = {conf->utempter_path, "add", NULL};
+    return spawn(reaper, NULL, argv, ptmx, ptmx, -1, NULL);
+}
+
+static bool
+del_utmp_record(const struct config *conf, struct reaper *reaper, int ptmx)
+{
+    if (ptmx < 0)
+        return true;
+    if (conf->utempter_path == NULL)
+        return true;
+
+    char *const argv[] = {conf->utempter_path, "del", NULL};
+    return spawn(reaper, NULL, argv, ptmx, ptmx, -1, NULL);
+}
+
 #if PTMX_TIMING
 static struct timespec last = {0};
 #endif
@@ -326,6 +350,7 @@ fdm_ptmx(struct fdm *fdm, int fd, int events, void *data)
     }
 
     if (hup) {
+        del_utmp_record(term->conf, term->reaper, term->ptmx);
         fdm_del(fdm, fd);
         term->ptmx = -1;
     }
@@ -1251,6 +1276,8 @@ term_init(const struct config *conf, struct fdm *fdm, struct reaper *reaper,
     }
     term->font_line_height = conf->line_height;
 
+    add_utmp_record(conf, reaper, ptmx);
+
     /* Start the slave/client */
     if ((term->slave = slave_spawn(
              term->ptmx, argc, term->cwd, argv, envp, &conf->env_vars,
@@ -1514,6 +1541,8 @@ term_shutdown(struct terminal *term)
     fdm_del(term->fdm, term->blink.fd);
     fdm_del(term->fdm, term->flash.fd);
 
+    del_utmp_record(term->conf, term->reaper, term->ptmx);
+
     if (term->window != NULL && term->window->is_configured)
         fdm_del(term->fdm, term->ptmx);
     else
@@ -1595,6 +1624,8 @@ term_destroy(struct terminal *term)
         }
     }
 
+    del_utmp_record(term->conf, term->reaper, term->ptmx);
+
     fdm_del(term->fdm, term->selection.auto_scroll.fd);
     fdm_del(term->fdm, term->render.app_sync_updates.timer_fd);
     fdm_del(term->fdm, term->render.title.timer_fd);

tests/test-config.c

@@ -458,6 +458,7 @@ test_section_main(void)
     test_string(&ctx, &parse_section_main, "shell", &conf.shell);
     test_string(&ctx, &parse_section_main, "term", &conf.term);
     test_string(&ctx, &parse_section_main, "app-id", &conf.app_id);
+    test_string(&ctx, &parse_section_main, "utempter", &conf.utempter_path);
 
     test_c32string(&ctx, &parse_section_main, "word-delimiters", &conf.word_delimiters);