udev_device_get_parent() caches the result of device_new_from_parent()
in udev_device->parent on first call. device_new_from_parent() sets
errno correctly via return_with_errno() when it fails, so a caller
gets the right errno on the first invocation. But on any subsequent
call for the same object, the cached NULL is returned directly without
recomputing anything, so errno reflects whatever happened in between
rather than the original failure reason.
Cache the errno alongside the parent pointer (new parent_errno field,
zero-initialized like the rest of the struct via udev_device_new()'s
compound literal) and restore it whenever the cached parent is NULL.
Previously, probe_superblocks() forwarded blkid_do_fullprobe()'s and
blkid_do_safeprobe()'s raw return code on error, which is just -1 with
no errno attached. The caller passes this value straight to
log_device_debug_errno() with %m, so a generic probing failure always
printed strerror(-1) regardless of what actually went wrong.
Convert the -1 error case to a proper negative errno via
errno_or_else(), matching the pattern used elsewhere in this file. The
'nothing found' (1) and success (0) return values are unchanged.
Repeats the enable/disable specifier-expansion check with 'systemctl
preset' instead. preset-all is intentionally not exercised here, since
$root accumulates unit files from earlier sections that are
deliberately invalid, and preset-all would trip on those unrelated
units.
Daniel28972897