When networkd starts or restarts, links are enumerated in ifindex
order. A slave enumerated before its master cannot register itself in
link_append_to_master(), as the master Link object does not exist yet.
The master then wrongly believes it has no slaves until the next
RTM_NEWLINK message for the slave arrives.
The stale slaves set affects operational state propagation
(degraded-carrier detection) and any code that inspects the slaves of
a master.
For instance, on restart, when networkd thinks that the master has no
slaves yet, we try to set the bond fail-over policy, which the kernel
then refuses because in reality the bond does have slaves.
To fix the issue, this updates the list of slaves after enumeration.
Co-authored-by: Yu Watanabe <watanabe.yu+github@gmail.com>
RamsesandYu Watanabe
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