Merge pull request #12267 from keszybz/udev-settle-warning

Udev settle warning

Author: poettering

man/rules/meson.build

@@ -775,6 +775,7 @@ manpages = [
    'systemd-tmpfiles-setup.service'],
   ''],
  ['systemd-tty-ask-password-agent', '1', [], ''],
+ ['systemd-udev-settle.service', '8', [], ''],
  ['systemd-udevd.service',
   '8',
   ['systemd-udevd',

man/systemd-udev-settle.service.xml

@@ -0,0 +1,51 @@
+<?xml version='1.0'?>
+<!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="systemd-udev-settle.service"
+          xmlns:xi="http://www.w3.org/2001/XInclude">
+
+  <refentryinfo>
+    <title>systemd-udev-settle.service</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>systemd-udev-settle.service</refentrytitle>
+    <manvolnum>8</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>systemd-udev-settle.service</refname>
+    <refpurpose>Wait for all pending udev events to be handled</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <para><filename>systemd-udev-settle.service</filename></para>
+  </refsynopsisdiv>
+
+  <refsect1><title>Description</title>
+  <para>This service calls <command>udevadm settle</command> to wait until all events that have been queued
+  by <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> have been
+  processed. It is a crude way to wait until "all" hardware has been discovered. Services may pull in this
+  service and order themselves after it to wait for the udev queue to be empty.</para>
+
+  <para><emphasis>Using this service is not recommended.</emphasis> There can be no guarantee that hardware
+  is fully discovered at any specific time, because the kernel does hardware detection asynchronously, and
+  certain busses and devices take a very long time to become ready, and also additional hardware may be
+  plugged in at any time. Instead, services should subscribe to udev events and react to any new hardware as
+  it is discovered. Services that, based on configuration, expect certain devices to appear, may warn or
+  report failure after a timeout. This timeout should be tailored to the hardware type. Waiting for
+  <filename>systemd-udev-settle.service</filename> usually slows boot significantly, because it means waiting
+  for all unrelated events too.</para>
+ </refsect1>
+
+  <refsect1>
+    <title>See Also</title>
+    <para>
+      <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+</refentry>

man/udevadm.xml

@@ -362,6 +362,10 @@
 
         <xi:include href="standard-options.xml" xpointer="help" />
       </variablelist>
+
+      <para>See
+      <citerefentry><refentrytitle>systemd-udev-settle.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+      for more information.</para>
     </refsect2>
 
     <refsect2><title>udevadm control <replaceable>option</replaceable></title>

src/udev/udevadm-settle.c

@@ -13,10 +13,16 @@
 #include <string.h>
 #include <unistd.h>
 
+#include "sd-bus.h"
+#include "sd-login.h"
+
 #include "libudev-util.h"
+#include "string-util.h"
+#include "strv.h"
 #include "time-util.h"
-#include "udevadm.h"
 #include "udev-ctrl.h"
+#include "udevadm.h"
+#include "unit-def.h"
 #include "util.h"
 #include "virt.h"
 
@@ -79,6 +85,61 @@ static int parse_argv(int argc, char *argv[]) {
         return 1;
 }
 
+static int emit_deprecation_warning(void) {
+        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        _cleanup_free_ char *unit = NULL, *unit_path = NULL;
+        _cleanup_strv_free_ char **a = NULL, **b = NULL;
+        int r;
+
+        r = sd_pid_get_unit(0, &unit);
+        if (r < 0 || !streq(unit, "systemd-udev-settle.service"))
+                return 0;
+
+        log_notice("systemd-udev-settle.service is deprecated.");
+
+        r = sd_bus_open_system(&bus);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to open system bus, skipping dependency queries: %m");
+
+        unit_path = unit_dbus_path_from_name("systemd-udev-settle.service");
+        if (!unit_path)
+                return -ENOMEM;
+
+        (void) sd_bus_get_property_strv(
+                        bus,
+                        "org.freedesktop.systemd1",
+                        unit_path,
+                        "org.freedesktop.systemd1.Unit",
+                        "WantedBy",
+                        NULL,
+                        &a);
+
+        (void) sd_bus_get_property_strv(
+                        bus,
+                        "org.freedesktop.systemd1",
+                        unit_path,
+                        "org.freedesktop.systemd1.Unit",
+                        "RequiredBy",
+                        NULL,
+                        &b);
+
+        r = strv_extend_strv(&a, b, true);
+        if (r < 0)
+                return r;
+
+        if (!strv_isempty(a)) {
+                _cleanup_free_ char *t = NULL;
+
+                t = strv_join(a, ", ");
+                if (!t)
+                        return -ENOMEM;
+
+                log_notice("Hint: please fix %s not to pull it in.", t);
+        }
+
+        return 0;
+}
+
 int settle_main(int argc, char *argv[], void *userdata) {
         _cleanup_(udev_queue_unrefp) struct udev_queue *queue = NULL;
         struct pollfd pfd;
@@ -128,6 +189,8 @@ int settle_main(int argc, char *argv[], void *userdata) {
                 .fd = r,
         };
 
+        (void) emit_deprecation_warning();
+
         for (;;) {
                 if (arg_exists && access(arg_exists, F_OK) >= 0)
                         return 0;

units/systemd-udev-settle.service.in

@@ -13,7 +13,7 @@
 
 [Unit]
 Description=udev Wait for Complete Device Initialization
-Documentation=man:udev(7) man:systemd-udevd.service(8)
+Documentation=man:systemd-udev-settle.service(8)
 DefaultDependencies=no
 Wants=systemd-udevd.service
 After=systemd-udev-trigger.service