sd-bus: Add sd_bus_list_names docs

The disk attributes can take some time to update on certain filesystems,
so let's strip them from inputs of both `homectl` and `userdbctl` before
comparing them to avoid unexpected fails.

Also, switch from `cmp` to `diff` to make a potential test fail a bit more
debuggable.

Fixes: #14755

TODO

@@ -22,6 +22,9 @@ Janitorial Clean-ups:
 
 Features:
 
+* homed: maybe pre-create ~/.cache as subvol so that it can have separate quota
+  easily?
+
 * journalctl --image= which is like --root= but operates on disk images
 
 * when systemd-nspawn and suchlike dissect an OS image, and there are multiple

man/rules/meson.build

@@ -263,6 +263,7 @@ manpages = [
   ''],
  ['sd_bus_get_n_queued_read', '3', ['sd_bus_get_n_queued_write'], ''],
  ['sd_bus_is_open', '3', ['sd_bus_is_ready'], ''],
+ ['sd_bus_list_names', '3', [], ''],
  ['sd_bus_message_append', '3', ['sd_bus_message_appendv'], ''],
  ['sd_bus_message_append_array',
   '3',

man/sd-bus.xml

@@ -86,6 +86,7 @@
 <citerefentry><refentrytitle>sd_bus_get_unique_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 <citerefentry><refentrytitle>sd_bus_is_bus_client</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 <citerefentry><refentrytitle>sd_bus_is_server</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+<citerefentry><refentrytitle>sd_bus_list_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 <citerefentry><refentrytitle>sd_bus_message_append_array</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 <citerefentry><refentrytitle>sd_bus_message_append_basic</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

man/sd_bus_list_names.xml

@@ -0,0 +1,111 @@
+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
+
+<refentry id="sd_bus_list_names"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
+
+  <refentryinfo>
+    <title>sd_bus_list_names</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>sd_bus_list_names</refentrytitle>
+    <manvolnum>3</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>sd_bus_list_names</refname>
+
+    <refpurpose>Retrieve information about registered names on a bus</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_list_names</function></funcdef>
+        <paramdef>sd_bus *<parameter>bus</parameter></paramdef>
+        <paramdef>char ***<parameter>acquired</parameter></paramdef>
+        <paramdef>char ***<parameter>activatable</parameter></paramdef>
+      </funcprototype>
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para><function>sd_bus_list_names()</function> retrieves information about the registered names on a bus.
+    If <parameter>acquired</parameter> is not <constant>NULL</constant>, this function calls
+    <ulink url="https://dbus.freedesktop.org/doc/dbus-specification.html#bus-messages-list-names">
+    org.freedesktop.DBus.ListNames</ulink> to retrieve the list of currently-owned names on the bus. If
+    <parameter>acquired</parameter> is not <constant>NULL</constant>, the function calls
+    <ulink url="https://dbus.freedesktop.org/doc/dbus-specification.html#bus-messages-list-activatable-names">
+    org.freedesktop.DBus.ListActivableNames</ulink> to retrieve the list of all names on the bus that can be
+    activated. Note that ownership of any string arrays returned by <function>sd_bus_list_names()</function>
+    is transferred to the caller and hence, the caller is responsible for freeing any results stored by
+    <function>sd_bus_list_names()</function> in <parameter>acquired</parameter> and
+    <parameter>activatable</parameter>.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Return Value</title>
+
+    <para>On success, <function>sd_bus_list_names()</function> returns a non-negative integer. On failure,
+    it returns a negative errno-style error code.</para>
+
+    <refsect2>
+      <title>Errors</title>
+
+      <para>Returned errors may indicate the following problems:</para>
+
+      <variablelist>
+        <varlistentry>
+          <term><constant>-EINVAL</constant></term>
+
+          <listitem><para><parameter>bus</parameter> or both <parameter>acquired</parameter> and
+          <parameter>activatable</parameter> were <constant>NULL</constant>.
+          </para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><constant>-ENOPKG</constant></term>
+
+          <listitem><para>The bus cannot be resolved.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><constant>-ECHILD</constant></term>
+
+          <listitem><para>The bus was created in a different process.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><constant>-ENOMEM</constant></term>
+
+          <listitem><para>Memory allocation failed.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><constant>-ENOTCONN</constant></term>
+
+          <listitem><para>The bus is not connected.</para></listitem>
+        </varlistentry>
+      </variablelist>
+    </refsect2>
+  </refsect1>
+
+  <xi:include href="libsystemd-pkgconfig.xml" />
+
+  <refsect1>
+    <title>See Also</title>
+
+    <para>
+      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+</refentry>

man/systemd.exec.xml

@@ -139,6 +139,9 @@
         <varname>PrivateDevices=</varname> below, as it may change the setting of
         <varname>DevicePolicy=</varname>.</para>
 
+        <para>Units making use of <varname>RootImage=</varname> automatically gain an
+        <varname>After=</varname> dependency on <filename>systemd-udevd.service</filename>.</para>
+
         <xi:include href="system-only.xml" xpointer="singular"/></listitem>
       </varlistentry>
 

src/basic/special.h

@@ -82,6 +82,7 @@
 #define SPECIAL_QUOTAON_SERVICE "quotaon.service"
 #define SPECIAL_REMOUNT_FS_SERVICE "systemd-remount-fs.service"
 #define SPECIAL_VOLATILE_ROOT_SERVICE "systemd-volatile-root.service"
+#define SPECIAL_UDEVD_SERVICE "systemd-udevd.service"
 
 /* Services systemd relies on */
 #define SPECIAL_DBUS_SERVICE "dbus.service"

src/core/unit.c

@@ -1079,6 +1079,15 @@ int unit_add_exec_dependencies(Unit *u, ExecContext *c) {
                         return r;
         }
 
+        if (c->root_image) {
+                /* We need to wait for /dev/loopX to appear when doing RootImage=, hence let's add an
+                 * implicit dependency on udev */
+
+                r = unit_add_dependency_by_name(u, UNIT_AFTER, SPECIAL_UDEVD_SERVICE, true, UNIT_DEPENDENCY_FILE);
+                if (r < 0)
+                        return r;
+        }
+
         if (!IN_SET(c->std_output,
                     EXEC_OUTPUT_JOURNAL, EXEC_OUTPUT_JOURNAL_AND_CONSOLE,
                     EXEC_OUTPUT_KMSG, EXEC_OUTPUT_KMSG_AND_CONSOLE,

test/units/testsuite-46.sh

@@ -9,9 +9,16 @@ if ! test -x /usr/bin/homectl ; then
 fi
 
 inspect() {
+        # As updating disk-size-related attributes can take some time on
+        # some filesystems, let's drop these fields before comparing the
+        # outputs to avoid unexpected fails. To see the full outputs of both
+        # homectl & userdbctl (for debugging purposes) drop the fields just
+        # before the comparison.
         homectl inspect $1 | tee /tmp/a
         userdbctl user $1 | tee /tmp/b
-        cmp /tmp/a /tmp/b
+
+        local PATTERN='/^\s*Disk (Size|Free|Floor|Ceiling):/d'
+        diff <(sed -r "$PATTERN" /tmp/a) <(sed -r "$PATTERN" /tmp/b)
         rm /tmp/a /tmp/b
 }