upgrade disables all serial devices and consoles

[Dan Streetman]

[impact]

when upgrading, all serial devices are changed to 'dead' and thus all serial consoles are stopped

[test case]

on a system configured with a serial console, upgrade from focal to the latest systemd package from upstream, and check the serial console. the state of the serial port and/or serial console can also be checked with systemctl status, e.g.:

$ systemctl status dev-ttyS0.device

[regression potential]

and regression would likely involve incorrectly detected or operational devices after a systemd version upgrade, or after a systemd pid1 reexec or reload.

[scope]

both upstream commits (ids below) are first included upstream in v247-rc1

[other info]

Upstream commit e77b146f825ef1bb63c297cc713962b94422d2c6 slightly altered the meaning of the 'G' sd-device db tag, to 'any' tag, and added a new 'Q' tag, meaning 'current' tag. When upgrading from udev before that commit to after the commit, the existing udev db is not updated, so the 'Q' tag is not present in the /run/udev/data/ db file for any previously-existing devices.

However, upstream commit 242c1c075aa284c8a8657c5aca36147f528146ba then changes the 'device_is_ready()' check in src/core/device.c to also check for the 'current' tag of 'systemd'. That tag will not be present for any devices in the system since udev just now was changed to know about the 'Q' type 'current' tags, and has not updated its /run/udev/data db files.

This leads to the systemd daemon-reexec ignoring all devices tagged with 'systemd', but only the older 'G' tag and not the new 'Q' tag, and marking them all as 'dead'.

[Dan Streetman (ddstreet)]

as this is needed only for the debian experimental branch (with v247-rc2), marking this as invalid for ubuntu.