Let's a concept of "rate limiting" to event sources: if specific event
sources fire too often in some time interval temporarily take them
offline, and take them back online once the interval passed.
This is a simple scheme of avoiding starvation of event sources if some
event source fires too often.
This introduces the new conceptual states of "offline" and "online" for
event sources: an event source is "online" only when enabled *and* not
ratelimited, and offline in all other cases. An event source that is
online hence has its fds registered in the epoll, its signals in the
signalfd and so on.
So far we used these fields to organize the earliest/latest timer event
priority queue. In a follow-up commit we want to introduce ratelimiting
to event sources, at which point we want any kind of event source to be
able to trigger time wakeups, and hence they all need to be included in
the earliest/latest prioqs. Thus, in preparation let's make this
generic.
No change in behaviour, just some shifting around of struct members from
the type-specific to the generic part.
sd_event_prepare() invokes callbacks that might drop the last user ref
on our event loop. Let's make sure we keep an explicit ref around it, so
that we won't end up with an invalid pointer. Similar in sd_event_run().
Basically, any function that is publically callable that might end up
invoking callbacks should ref the relevant objects to be protected
against callbacks destroying these objects while we still want to access
them. We did this correctly in sd_event_dispatch() and sd_event_loop(),
but these are not the only ones which are callable from the outside.
If /sys/class/OOO node is created and destroyed during booting (kernle driver initialization fails),
systemd-udev-trigger.service fails due to race condition.
***** race condition ***********************************************************************************
1. kernel driver create /sys/class/OOO
2. systemd-udev-trigger.service execues "/usr/bin/udevadm trigger --type=devices --action=add"
3. device_enumerator_scan_devices() => enumerator_scan_devices_all() => enumerator_scan_dir("class") =>
opendir("/sys/class") and iterate all subdirs ==> enumerator_scan_dir_and_add_devices("/sys/class/OOO")
4. kernel driver fails and destroy /sys/class/OOO
5. enumerator_scan_dir_and_add_devices("/sys/class/OOO") fails in opendir("/sys/class/OOO")
6. "systemd-udev-trigger.service" fails
7. udev coldplug fails and some device units not ready
8. mount units asociated with device units fail
9. local-fs.target fails
10. enters emergency mode
********************************************************************************************************
***** status of systemd-udev-trigger.service unit ******************************************************
$ systemctl status systemd-udev-trigger.service
systemd-udev-trigger.service - udev Coldplug all Devices
Loaded: loaded (/usr/lib/systemd/system/systemd-udev-trigger.service; static; vendor preset: enabled)
Active: failed (Result: exit-code) since Thu 2020-01-02 13:16:54 KST; 22min ago
Docs: man:udev(7)
man:systemd-udevd.service(8)
Process: 2162 ExecStart=/usr/bin/udevadm trigger --type=subsystems --action=add (code=exited, status=0/SUCCESS)
Process: 2554 ExecStart=/usr/bin/udevadm trigger --type=devices --action=add (code=exited, status=1/FAILURE)
Main PID: 2554 (code=exited, status=1/FAILURE)
Jan 02 13:16:54 localhost udevadm[2554]: Failed to scan devices: No such file or directory
Jan 02 13:16:54 localhost systemd[1]: systemd-udev-trigger.service: Main process exited, code=exited, status=1/FAILURE
Jan 02 13:16:54 localhost systemd[1]: systemd-udev-trigger.service: Failed with result 'exit-code'.
Jan 02 13:16:54 localhost systemd[1]: Failed to start udev Coldplug all Devices.
*******************************************************************************************************
***** journal log with Environment=SYSTEMD_LOG_LEVEL=debug in systemd-udev-trigger.service ***********
Jan 01 21:57:20 localhost udevadm[2039]: sd-device-enumerator: Scanning /sys/bus
Jan 01 21:57:20 localhost udevadm[2522]: sd-device-enumerator: Scan all dirs
Jan 01 21:57:20 localhost udevadm[2522]: sd-device-enumerator: Scanning /sys/bus
Jan 01 21:57:21 localhost udevadm[2522]: sd-device-enumerator: Scanning /sys/class
Jan 01 21:57:21 localhost udevadm[2522]: sd-device-enumerator: Failed to scan /sys/class: No such file or directory
Jan 01 21:57:21 localhost udevadm[2522]: Failed to scan devices: No such file or directory
*******************************************************************************************************
... when called with a valid environment variable name. This means that
any time we call it with a fixed string, it is guaranteed to return 0.
(Also when the variable is not present in the environment block.)
Coverity in CID#1435966 was complaining that s->enabled is not "restored" in
all cases. But the code was actually correct, since it should only be
"restored" in the error paths. But let's still make this prettier by not setting
the state before all operations that may fail are done.
We need to set .enabled for the prioq reshuffling operations, so move those down.
No functional change intended.
Hardware addresses come in various shapes and sizes, these new functions
and accomapying data structures account for that instead of hard-coding
a hardware address to the 6 bytes of an ethernet MAC.
So far half of sd_event_source_set_enabled() was doing enabling, the
other half was doing disabling. Let's split that into two separate
calls.
(This also adds a new shortcut to sd_event_source_set_enabled(): if the
caller toggles between "ON" and "ONESHOT" we'll now shortcut this, since
the event source is already enabled in that case and shall remain
enabled.)
This heavily borrows and is inspired from Michal Sekletár's #17284
refactoring.
We typically don't just reshuffle a single prioq at once, but always
two. Let's add two helper functions that do this, and reuse them
everywhere.
(Note that this drops one minor optimization:
sd_event_source_set_time_accuracy() previously only reshuffled the
"latest" prioq, since changing the accuracy has no effect on the
earliest time of an event source, just the latest time an event source
can run. This optimization is removed to simplify things, given that
it's not really worth the effort as prioq_reshuffle() on properly
ordered prioqs has practically zero cost O(1)).
(Slightly generalized, commented and split out of #17284 by Lennart)
Ubuntu builds on the Launchpad infrastructure run inside a chroot that does
not have the sysfs cgroup dirs mounted, so this call will return ENOMEDIUM
from cg_unified_cached() during the build-time testing, for example when
building the package in a Launchpad PPA.
So far we didn't allow empty properties, but it makes sense to do so, for
example to distinguish empty data from lack of data. It also makes it easy to
override properties (back to the empty) value for specific cases.
Add a new ID128_PLAIN_OR_UNINIT format which treats the string
"uninitialized" like the file was empty and return -ENOMEDIUM. This
format should be used when reading an /etc/machine-id file from an image
that is not currently running.
This might fix#17025:
> the call trace is
> bus_ensure_running -> sd_bus_process -> bus_process_internal -> process_closeing --> sd_bus_close
> |
> \-> process_match
We ended doing callouts to the Disconnected matches from bus_ensure_running()
and shouldn't. bus_ensure_running() should never do callouts. This change
should fix this however: once we notice that the connection is going down we
will now fail instantly with ENOTOCONN instead of calling any callbacks.
We would return ENOENT, which is extremely confusing. Strace is not helpful because
no *file* is actually missing. So let's add some logs at debug level and also use
a custom return code. Let all user-facing utilities print a custom error message
in that case.
When connection to the bus fails it can be mighty hard to figure out
what went wrong because we have many different connection mechanisms and
we don't log what is happenning.
