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timer: add new feature FixedRandomDelay=

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FixedRandomDelay=yes will use
`siphash24(sd_id128_get_machine() || MANAGER_IS_SYSTEM(m) || getuid() || u->id)`,
where || is concatenation, instead of a random number to choose a value between
0 and RandomizedDelaySec= as the timer delay.
This essentially sets up a fixed, but seemingly random, offset for each timer
iteration rather than having a random offset recalculated each time it fires.

Closes #10355

Co-author: Anita Zhang <the.anitazha@gmail.com>
This commit is contained in:
Kristijan Gjoshev 2020-02-01 18:27:08 +01:00 committed by Anita Zhang
parent 5cecbae158
commit acf24a1a84
10 changed files with 62 additions and 2 deletions
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1
docs/TRANSIENT-SETTINGS.md
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@ -374,6 +374,7 @@ Most timer unit settings are available to transient units.
✓ RemainAfterElapse=
✓ AccuracySec=
✓ RandomizedDelaySec=
✓ FixedRandomDelay=
Unit=
```

6
man/org.freedesktop.systemd1.xml
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@ -7211,6 +7211,8 @@ node /org/freedesktop/systemd1/unit/systemd_2dtmpfiles_2dclean_2etimer {
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly t RandomizedDelayUSec = ...;
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly b FixedRandomDelay = ...;
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly b Persistent = ...;
@org.freedesktop.DBus.Property.EmitsChangedSignal("const")
readonly b WakeSystem = ...;
@ -7236,6 +7238,8 @@ node /org/freedesktop/systemd1/unit/systemd_2dtmpfiles_2dclean_2etimer {
<!--property RandomizedDelayUSec is not documented!-->
<!--property FixedRandomDelay is not documented!-->
<!--property Persistent is not documented!-->
<!--property WakeSystem is not documented!-->
@ -7276,6 +7280,8 @@ node /org/freedesktop/systemd1/unit/systemd_2dtmpfiles_2dclean_2etimer {
<variablelist class="dbus-property" generated="True" extra-ref="RandomizedDelayUSec"/>
<variablelist class="dbus-property" generated="True" extra-ref="FixedRandomDelay"/>
<variablelist class="dbus-property" generated="True" extra-ref="Persistent"/>
<variablelist class="dbus-property" generated="True" extra-ref="WakeSystem"/>

12
man/systemd.timer.xml
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@ -268,6 +268,18 @@
<varname>AccuracySec=1us</varname>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>FixedRandomDelay=</varname></term>
<listitem><para>Takes a boolean argument. If true, some amount of time between 0 and
<varname>RandomizedDelaySec=</varname> is chosen and added as the delay for each timer iteration. As this
delay will not be recalculated on each run, this effectively creates a fixed offset for each iteration.
The distribution between 0 and <varname>RandomizedDelaySec=</varname> is deterministic and based on
a combination of the machine ID, whether the timer is run by the user/system manager, the service manager's
user ID, and the timer's unit name. Has no effect if
<varname>RandomizedDelaySec=</varname> is set to 0. Defaults to <option>false</option>.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>OnClockChange=</varname></term>
<term><varname>OnTimezoneChange=</varname></term>

4
src/core/dbus-timer.c
View File

@ -131,6 +131,7 @@ const sd_bus_vtable bus_timer_vtable[] = {
SD_BUS_PROPERTY("Result", "s", property_get_result, offsetof(Timer, result), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
SD_BUS_PROPERTY("AccuracyUSec", "t", bus_property_get_usec, offsetof(Timer, accuracy_usec), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("RandomizedDelayUSec", "t", bus_property_get_usec, offsetof(Timer, random_usec), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("FixedRandomDelay", "b", bus_property_get_bool, offsetof(Timer, fixed_random_delay), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("Persistent", "b", bus_property_get_bool, offsetof(Timer, persistent), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("WakeSystem", "b", bus_property_get_bool, offsetof(Timer, wake_system), SD_BUS_VTABLE_PROPERTY_CONST),
SD_BUS_PROPERTY("RemainAfterElapse", "b", bus_property_get_bool, offsetof(Timer, remain_after_elapse), SD_BUS_VTABLE_PROPERTY_CONST),
@ -232,6 +233,9 @@ static int bus_timer_set_transient_property(
if (streq(name, "RandomizedDelayUSec"))
return bus_set_transient_usec(u, name, &t->random_usec, message, flags, error);
if (streq(name, "FixedRandomDelay"))
return bus_set_transient_bool(u, name, &t->fixed_random_delay, message, flags, error);
if (streq(name, "WakeSystem"))
return bus_set_transient_bool(u, name, &t->wake_system, message, flags, error);

1
src/core/load-fragment-gperf.gperf.m4
View File

@ -481,6 +481,7 @@ Timer.OnTimezoneChange, config_parse_bool,
Timer.Persistent, config_parse_bool, 0, offsetof(Timer, persistent)
Timer.WakeSystem, config_parse_bool, 0, offsetof(Timer, wake_system)
Timer.RemainAfterElapse, config_parse_bool, 0, offsetof(Timer, remain_after_elapse)
Timer.FixedRandomDelay, config_parse_bool, 0, offsetof(Timer, fixed_random_delay)
Timer.AccuracySec, config_parse_sec, 0, offsetof(Timer, accuracy_usec)
Timer.RandomizedDelaySec, config_parse_sec, 0, offsetof(Timer, random_usec)
Timer.Unit, config_parse_trigger_unit, 0, 0

34
src/core/timer.c
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@ -169,6 +169,36 @@ static int timer_setup_persistent(Timer *t) {
return 0;
}
static uint64_t timer_get_fixed_delay_hash(Timer *t) {
static const uint8_t hash_key[] = {
0x51, 0x0a, 0xdb, 0x76, 0x29, 0x51, 0x42, 0xc2,
0x80, 0x35, 0xea, 0xe6, 0x8e, 0x3a, 0x37, 0xbd
};
struct siphash state;
sd_id128_t machine_id;
uid_t uid;
int r;
assert(t);
uid = getuid();
r = sd_id128_get_machine(&machine_id);
if (r < 0) {
log_unit_debug_errno(UNIT(t), r,
"Failed to get machine ID for the fixed delay calculation, proceeding with 0: %m");
machine_id = SD_ID128_NULL;
}
siphash24_init(&state, hash_key);
siphash24_compress(&machine_id, sizeof(sd_id128_t), &state);
siphash24_compress_boolean(MANAGER_IS_SYSTEM(UNIT(t)->manager), &state);
siphash24_compress(&uid, sizeof(uid_t), &state);
siphash24_compress_string(UNIT(t)->id, &state);
return siphash24_finalize(&state);
}
static int timer_load(Unit *u) {
Timer *t = TIMER(u);
int r;
@ -215,6 +245,7 @@ static void timer_dump(Unit *u, FILE *f, const char *prefix) {
"%sWakeSystem: %s\n"
"%sAccuracy: %s\n"
"%sRemainAfterElapse: %s\n"
"%sFixedRandomDelay: %s\n"
"%sOnClockChange: %s\n"
"%sOnTimeZoneChange: %s\n",
prefix, timer_state_to_string(t->state),
@ -224,6 +255,7 @@ static void timer_dump(Unit *u, FILE *f, const char *prefix) {
prefix, yes_no(t->wake_system),
prefix, format_timespan(buf, sizeof(buf), t->accuracy_usec, 1),
prefix, yes_no(t->remain_after_elapse),
prefix, yes_no(t->fixed_random_delay),
prefix, yes_no(t->on_clock_change),
prefix, yes_no(t->on_timezone_change));
@ -332,7 +364,7 @@ static void add_random(Timer *t, usec_t *v) {
if (*v == USEC_INFINITY)
return;
add = random_u64() % t->random_usec;
add = (t->fixed_random_delay ? timer_get_fixed_delay_hash(t) : random_u64()) % t->random_usec;
if (*v + add < *v) /* overflow */
*v = (usec_t) -2; /* Highest possible value, that is not USEC_INFINITY */

1
src/core/timer.h
View File

@ -59,6 +59,7 @@ struct Timer {
bool remain_after_elapse;
bool on_clock_change;
bool on_timezone_change;
bool fixed_random_delay;
char *stamp_path;
};

3
src/shared/bus-unit-util.c
View File

@ -2074,7 +2074,8 @@ static int bus_append_timer_property(sd_bus_message *m, const char *field, const
"RemainAfterElapse",
"Persistent",
"OnTimezoneChange",
"OnClockChange"))
"OnClockChange",
"FixedRandomDelay"))
return bus_append_parse_boolean(m, field, eq);
if (STR_IN_SET(field, "AccuracySec",

1
test/fuzz/fuzz-unit-file/directives.service
View File

@ -175,6 +175,7 @@ PipeSize=
Priority=
PropagatesReloadTo=
RandomizedDelaySec=
FixedRandomDelay=
RebootArgument=
ReceiveBuffer=
RefuseManualStart=

1
test/fuzz/fuzz-unit-file/systemd-tmpfiles-clean.timer
View File

@ -32,6 +32,7 @@ OnCalendar=Fri 2012-11-23 11:12:13
Persistent=true
AccuracySec=24h
RandomizedDelaySec=234234234
FixedRandomDelay=true
Persistent=no
Unit=foo.service