login: make hold-off timeout configurable

This introduces 'HoldoffTimeoutSec' to logind.conf to make
IGNORE_LID_SWITCH_{SUSPEND,STARTUP}_USEC configurable.

Background: If an external monitor is connected, or if the system is
docked, we want to ignore LID events. This is required to support setups
where a laptop is used with external peripherals while the LID is closed.
However, this requires us to probe all hot-plugged devices before reacting
to LID events. But with modern buses like USB, the standards do not impose
any timeout on the slots, so we have no chance to know whether a given
slot is used or not. Hence, after resume and startup, we have to wait a
fixed timeout to give the kernel a chance to probe devices. Our timeout
has always been generous enough to support even the slowest devices.
However, a lot of people didn't use these features and wanted to disable
the hold-off timer. Now we provide a knob to do that.

man/logind.conf.xml

@@ -250,6 +250,21 @@
         sleep keys do. </para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><varname>HoldoffTimeoutSec=</varname></term>
+
+        <listitem><para>Specifies the timeout after system startup or
+        system resume in which systemd will hold off on reacting to
+        LID events. This is required for the system to properly
+        detect any hotplugged devices so systemd can ignore LID events
+        if external monitors, or docks, are connected. If set to 0,
+        systemd will always react immediately, possibly before the
+        kernel fully probed all hotplugged devices. This is safe, as
+        long as you do not care for systemd to account for devices
+        that have been plugged or unplugged while the system was off.
+        Defaults to 30s.</para></listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><varname>RuntimeDirectorySize=</varname></term>
 

src/login/logind-dbus.c

@@ -1448,7 +1448,7 @@ static int execute_shutdown_or_sleep(
         m->action_what = w;
 
         /* Make sure the lid switch is ignored for a while */
-        manager_set_lid_switch_ignore(m, now(CLOCK_MONOTONIC) + IGNORE_LID_SWITCH_SUSPEND_USEC);
+        manager_set_lid_switch_ignore(m, now(CLOCK_MONOTONIC) + m->holdoff_timeout_usec);
 
         return 0;
 }
@@ -1979,6 +1979,7 @@ const sd_bus_vtable manager_vtable[] = {
         SD_BUS_PROPERTY("HandleHibernateKey", "s", property_get_handle_action, offsetof(Manager, handle_hibernate_key), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("HandleLidSwitch", "s", property_get_handle_action, offsetof(Manager, handle_lid_switch), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("HandleLidSwitchDocked", "s", property_get_handle_action, offsetof(Manager, handle_lid_switch_docked), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("HoldoffTimeoutUSec", "t", NULL, offsetof(Manager, holdoff_timeout_usec), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("IdleAction", "s", property_get_handle_action, offsetof(Manager, idle_action), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("IdleActionUSec", "t", NULL, offsetof(Manager, idle_action_usec), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("PreparingForShutdown", "b", property_get_preparing, 0, 0),

src/login/logind-gperf.gperf

@@ -29,6 +29,7 @@ Login.PowerKeyIgnoreInhibited,     config_parse_bool,          0, offsetof(Manag
 Login.SuspendKeyIgnoreInhibited,   config_parse_bool,          0, offsetof(Manager, suspend_key_ignore_inhibited)
 Login.HibernateKeyIgnoreInhibited, config_parse_bool,          0, offsetof(Manager, hibernate_key_ignore_inhibited)
 Login.LidSwitchIgnoreInhibited,    config_parse_bool,          0, offsetof(Manager, lid_switch_ignore_inhibited)
+Login.HoldoffTimeoutSec,           config_parse_sec,           0, offsetof(Manager, holdoff_timeout_usec)
 Login.IdleAction,                  config_parse_handle_action, 0, offsetof(Manager, idle_action)
 Login.IdleActionSec,               config_parse_sec,           0, offsetof(Manager, idle_action_usec)
 Login.RuntimeDirectorySize,        config_parse_tmpfs_size,    0, offsetof(Manager, runtime_dir_size)

src/login/logind.c

@@ -54,6 +54,7 @@ Manager *manager_new(void) {
         m->handle_lid_switch = HANDLE_SUSPEND;
         m->handle_lid_switch_docked = HANDLE_IGNORE;
         m->lid_switch_ignore_inhibited = true;
+        m->holdoff_timeout_usec = 30 * USEC_PER_SEC;
 
         m->idle_action_usec = 30 * USEC_PER_MINUTE;
         m->idle_action = HANDLE_IGNORE;
@@ -1029,7 +1030,7 @@ int manager_startup(Manager *m) {
         if (r < 0)
                 return log_error_errno(r, "Failed to add seat0: %m");
 
-        r = manager_set_lid_switch_ignore(m, 0 + IGNORE_LID_SWITCH_STARTUP_USEC);
+        r = manager_set_lid_switch_ignore(m, 0 + m->holdoff_timeout_usec);
         if (r < 0)
                 log_warning_errno(r, "Failed to set up lid switch ignore event source: %m");
 

src/login/logind.conf

@@ -27,6 +27,7 @@
 #SuspendKeyIgnoreInhibited=no
 #HibernateKeyIgnoreInhibited=no
 #LidSwitchIgnoreInhibited=yes
+#HoldoffTimeoutSec=30s
 #IdleAction=ignore
 #IdleActionSec=30min
 #RuntimeDirectorySize=10%

src/login/logind.h

@@ -37,9 +37,6 @@ typedef struct Manager Manager;
 #include "logind-button.h"
 #include "logind-action.h"
 
-#define IGNORE_LID_SWITCH_STARTUP_USEC (3 * USEC_PER_MINUTE)
-#define IGNORE_LID_SWITCH_SUSPEND_USEC (30 * USEC_PER_SEC)
-
 struct Manager {
         sd_event *event;
         sd_bus *bus;
@@ -120,6 +117,7 @@ struct Manager {
 
         Hashmap *polkit_registry;
 
+        usec_t holdoff_timeout_usec;
         sd_event_source *lid_switch_ignore_event_source;
 
         size_t runtime_dir_size;