Debugging udev issues especially during the early boot is fairly
difficult. Currently, you need to enable (at least) debug logging and
start monitoring uevents, try to reproduce the issue and then analyze
and correlate two (usually) huge log files. This is not ideal.
This patch aims to provide much more focused debugging tool,
tracepoints. More often then not we tend to have at least the basic idea
about the issue we are trying to debug further, e.g. we know it is
storage related. Hence all of the debug data generated for network
devices is useless, adds clutter to the log files and generally
slows things down.
Using this set of tracepoints you can start asking very specific
questions related to event processing for given device or subsystem.
Tracepoints can be used with various tracing tools but I will provide
examples using bpftrace.
Another important aspect to consider is that using tracepoints you can
debug production systems. There is no need to install test packages with
added logging, no debuginfo packages, etc...
Example usage (you might be asking such questions during the debug session),
Q: How can I list all tracepoints?
A: bpftrace -l 'usdt:/usr/lib/systemd/systemd-udevd:udev:*'
Q: What are the arguments for each tracepoint?
A: Look at the code and search for use of DEVICE_TRACE_POINT macro.
Q: How many times we have executed external binary?
A: bpftrace -e 'usdt:/usr/lib/systemd/systemd-udevd:udev:spawn_exec { @cnt = count(); }'
Q: What binaries where executed while handling events for "dm-0" device?
A bpftrace -e 'usdt:/usr/lib/systemd/systemd-udevd:udev:spawn_exec / str(arg1) == "dm-0"/ { @cmds[str(arg4)] = count(); }'
Thanks to Thomas Weißschuh <thomas@t-8ch.de> for reviewing this patch
and contributions that allowed us to drop the dependency on dtrace tool
and made the resulting code much more concise.
This makes the last 11 chars are always preserved for hashed string.
So, it is hard to generate a path which conflicts to another path.
Fixes an issue demonstrated in the previous commit.
The commit e64943363a introduces hashed
path at the end of the filename. But we can easily generate the path
which conflicts another path. The issue will be fixed in later commit.
This adds two things:
- A new switch --uuid is added to "udevadm trigger". If specified a
random UUID is associated with the synthettic uevent and it is printed
to stdout. It may then be used manually to match up uevents as they
propagate through the system.
- The UUID logic is now implicitly enabled if "udevadm trigger --settle"
is used, in order to wait for precisely the uevents we actually
trigger. Fallback support is kept for pre-4.13 kernels (where the
requests for trigger uevents with uuids results in EINVAL).
There are nothing we can configure in udevd for loopback interfaces;
no ethertool configs can be applied, MAC address, interface name should
not be touched.
ethtool_set_glinksettings() already fallback to use ETHTOOL_GSET/ETHTOOL_SSET
commands when ETHTOOL_GLINKSETTINGS/ETHTOOL_SLINKSETTINGS are not
supported.
We recently started making more use of malloc_usable_size() and rely on
it (see the string_erase() story). Given that we don't really support
sytems where malloc_usable_size() cannot be trusted beyond statistics
anyway, let's go fully in and rework GREEDY_REALLOC() on top of it:
instead of passing around and maintaining the currenly allocated size
everywhere, let's just derive it automatically from
malloc_usable_size().
I am mostly after this for the simplicity this brings. It also brings
minor efficiency improvements I guess, but things become so much nicer
to look at if we can avoid these allocation size variables everywhere.
Note that the malloc_usable_size() man page says relying on it wasn't
"good programming practice", but I think it does this for reasons that
don't apply here: the greedy realloc logic specifically doesn't rely on
the returned extra size, beyond the fact that it is equal or larger than
what was requested.
(This commit was supposed to be a quick patch btw, but apparently we use
the greedy realloc stuff quite a bit across the codebase, so this ends
up touching *a*lot* of code.)
Previously, watch handle is saved in the udev databse. But in most cases,
the handle saved in the database is not updated. Especially, when udevd
is restarted, the inotify watch is restarted, but the database is not
updated.
Moreover, it is not necessary to save watch handle in the database, as
the handle is only take a effect during udevd is running, and the value
is meaningless when udevd is restarted.
So, this makes the opposite map from device ID to watch handle is saved
in /run/udev/watch as a symbolic link, and the handle not saved in the
database anymore.
Fixes#18525.
Some udev rule may erroneously set inotify watch on remove event.
For safety, silently ignore such an inotify watch enablement.
This also moves inotify watch enablement code to udev-event.c.
When udev rules are not applied correctly, then run program lists is
not perfect. So, udev_event_execute_run() later in
worker_process_device() should not be called.
When manager_exit() or manager_free() is called, the global variable in
udev-watch.c is not set '-1'. Of course, that is safe, as the event source
for the inotify fd is unref()ed in manager_exit() and manager_free().
But let's not store fd globally.
Yu Watanabe
Michal Sekletár
Lennart Poettering
Zbigniew Jędrzejewski-Szmek
Jörg Thalheim