update TODO

Fixes: #16439
Alternative-To: #16440

TODO

@@ -17,6 +17,10 @@ Janitorial Clean-ups:
 
 Features:
 
+* complement root=, rootflags=, rootfstype= with rootsubdir= which allows
+  mounting a subdir of the root fs as actual root. This can be used as
+  fstype-agnostic version of btrfs' rootflags=subvol=foobar.
+
 * add --copy-from and --copy-to command to systemd-dissect which copies stuff
   in and out of a disk image
 
@@ -24,9 +28,6 @@ Features:
 
 * if /usr/bin/swapoff fails due to OOM, log a friendly explanatory message about it
 
-* add loud warning to the logs (with catalog entry) if systemd-udev-settle is
-  pulled into the boot process
-
 * build short web pages out of each catalog entry, build them along with man
   pages, and include hyperlinks to them in the journal output
 

catalog/systemd.catalog.in

@@ -484,3 +484,36 @@ It is strongly recommended to avoid running services under this user identity,
 in particular on systems using NFS or running containers. Allocate a user ID
 specific to this service, either statically via systemd-sysusers or dynamically
 via the DynamicUser= service setting.
+
+-- 1c0454c1bd2241e0ac6fefb4bc631433
+Subject: systemd-udev-settle.service is deprecated.
+Defined-By: systemd
+Support: %SUPPORT_URL%
+
+Usage of the systemd service unit systemd-udev-settle.service is deprecated. It
+inserts artificial delays into the boot process without providing the
+guarantees other subsystems traditionally assumed it provides. Relying on this
+service is racy, and it is generally a bug to make use of it and depend on it.
+
+Traditionally, this service's job was to wait until all devices a system
+possesses have been fully probed and initialized, delaying boot until this
+phase is completed. However, today's systems and hardware generally don't work
+this way anymore, hardware today may show up any time and take any time to be
+probed and initialized. Thus, in the general case, it's no longer possible to
+correctly delay boot until "all devices" have been processed, as it is not
+clear what "all devices" means and when they have been found. This is in
+particular the case if USB hardware or network-attached hardware is used.
+
+Modern software that requires some specific hardware (such as a network device
+or block device) to operate should only wait for the specific devices it needs
+to show up, and otherwise operate asynchronously initializing devices as they
+appear during boot and during runtime without delaying the boot process.
+
+It is a defect of the software in question if it doesn't work this way, and
+still pulls systemd-udev-settle.service into the boot process.
+
+Please file a bug report against the following units, with a request for it to
+be updated to operate in a hotplug fashion without depending on
+systemd-udev-settle.service:
+
+    @OFFENDING_UNITS@

src/analyze/analyze-condition.c

@@ -85,11 +85,14 @@ static int parse_condition(Unit *u, const char *line) {
                 p = startswith(line, c->name);
                 if (!p)
                         continue;
-                p += strspn(p, WHITESPACE);
-                if (*p != '=')
-                        return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Expected \"=\" in \"%s\".", line);
 
-                p += 1 + strspn(p + 1, WHITESPACE);
+                p += strspn(p, WHITESPACE);
+
+                if (*p != '=')
+                        continue;
+                p++;
+
+                p += strspn(p, WHITESPACE);
 
                 return c->parser(NULL, "(stdin)", 0, NULL, 0, c->name, c->type, p, target, u);
         }

src/systemd/sd-messages.h

@@ -170,6 +170,11 @@ _SD_BEGIN_DECLARATIONS;
 #define SD_MESSAGE_NOBODY_USER_UNSUITABLE_STR \
                                           SD_ID128_MAKE_STR(b4,80,32,5f,9c,39,4a,7b,80,2c,23,1e,51,a2,75,2c)
 
+#define SD_MESSAGE_SYSTEMD_UDEV_SETTLE_DEPRECATED \
+                                          SD_ID128_MAKE(1c,04,54,c1,bd,22,41,e0,ac,6f,ef,b4,bc,63,14,33)
+#define SD_MESSAGE_SYSTEMD_UDEV_SETTLE_DEPRECATED_STR \
+                                          SD_ID128_MAKE_STR(1c,04,54,c1,bd,22,41,e0,ac,6f,ef,b4,bc,63,14,33)
+
 _SD_END_DECLARATIONS;
 
 #endif

src/udev/udevadm-settle.c

@@ -14,7 +14,9 @@
 
 #include "sd-bus.h"
 #include "sd-login.h"
+#include "sd-messages.h"
 
+#include "bus-util.h"
 #include "io-util.h"
 #include "libudev-util.h"
 #include "string-util.h"
@@ -87,19 +89,25 @@ static int parse_argv(int argc, char *argv[]) {
 
 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;
+        _cleanup_strv_free_ char **a = NULL;
+        _cleanup_free_ char *unit = NULL;
         int r;
 
         r = sd_pid_get_unit(0, &unit);
-        if (r < 0 || !streq(unit, "systemd-udev-settle.service"))
+        if (r < 0) {
+                log_debug_errno(r, "Failed to determine unit we run in, ignoring: %m");
+                return 0;
+        }
+
+        if (!streq(unit, "systemd-udev-settle.service"))
                 return 0;
 
-        log_notice("systemd-udev-settle.service is deprecated.");
-
-        r = sd_bus_open_system(&bus);
+        r = bus_connect_system_systemd(&bus);
         if (r < 0)
-                return log_debug_errno(r, "Failed to open system bus, skipping dependency queries: %m");
+                log_debug_errno(r, "Failed to open connection to systemd, skipping dependency queries: %m");
+        else {
+                _cleanup_strv_free_ char **b = NULL;
+                _cleanup_free_ char *unit_path = NULL;
 
                 unit_path = unit_dbus_path_from_name("systemd-udev-settle.service");
                 if (!unit_path)
@@ -126,15 +134,24 @@ static int emit_deprecation_warning(void) {
                 r = strv_extend_strv(&a, b, true);
                 if (r < 0)
                         return r;
+        }
 
-        if (!strv_isempty(a)) {
+        if (strv_isempty(a))
+                /* Print a simple message if we cannot determine the dependencies */
+                log_notice("systemd-udev-settle.service is deprecated.");
+        else {
+                /* Print a longer, structured message if we can acquire the dependencies (this should be the
+                 * common case). This is hooked up with a catalog entry and everything. */
                 _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);
+                log_struct(LOG_NOTICE,
+                           "MESSAGE=systemd-udev-settle.service is deprecated. Please fix %s not to pull it in.", t,
+                           "OFFENDING_UNITS=%s", t,
+                           "MESSAGE_ID=" SD_MESSAGE_SYSTEMD_UDEV_SETTLE_DEPRECATED_STR);
         }
 
         return 0;

test/meson.build

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: LGPL-2.1+
 
+if install_tests
         testdata_dir = testsdir + '/testdata/'
 
         install_subdir('journal-data',
@@ -51,6 +52,7 @@ endif
         install_data('create-busybox-container',
                      install_mode : 'rwxr-xr-x',
                      install_dir : testdata_dir)
+endif
 
 test_network_generator_conversion_sh = find_program('test-network-generator-conversion.sh')