Let's put this back in, as it could help with occasional machine lock ups
on overloaded systems (and it didn't help with the original issue
anyway).
This reverts commit 3a89904e45.
The pkcs11 uri is no set if the smart card is not inserted while using
`pkcs11-uri=auto` with libcryptsetup plugins.
```
> systemd-cryptsetup attach cr_data /dev/sda1 - pkcs11-uri=auto
Set cipher aes, mode xts-plain64, key size 512 bits for device /dev/sda1.
Security token (null) not present for unlocking volume Linux filesystem (cr_data), please plug it in.
```
All the following commands would just fail with -ENOANO anyway, hence
there's no point in sending them. And it allows us to shave off some
error handling code.
This is mostly just refactoring to make the code more manageable and
extendable. It doesn't introduce any semantic changes, but it
"optimizes" the communication with udevd a bit:
* If an option is used multiple times, only one command will be sent. If
the option takes a value, the value of the final appearance of the
option is used. The only exception is --property, which is additive by
nature.
* Options --start-exec-queue and --stop-exec-queue are handled together.
Only one of START_QUEUE/STOP_QUEUE commands will be sent to udevd even
if both options appear on the command line.
Before confext was added, hierarchies always existed in extensions. Now
they are optional - i.e., a sysext will not contain /etc/. So mixing a
confext and a sysext fails, as we'll try to create an overlay with /etc/
from the base, the confext and the sysext, but the latter doesn't have
the directory.
After the source images are mounted, check that each hierarchy exists in
each source image before creating the overlay, and drop them if they
don't.
Follow-up for 55ea4ef096
Let's install a simple no-op signal handler without SA_RESTART for
SIGINT/SIGTERM, which allows us to interrupt read_one_char() and follow
it up with a proper cleanup, including restoring the vt to the original
state.
Resolves: #29478
Introduce a new env variable $SYSTEMD_NSPAWN_CHECK_OS_RELEASE, that can
be used to disable the os-release check for bootable OS trees. Useful
when trying to boot a container with empty /etc/ and bind-mounted /usr/.
Resolves: #29185
