Cannot read/write long events from journald (affects docker compat API /containers/(id or name)/wait)

[matejvasek]

It is not possible to read/write some events for entries with huge labels map.

Log contains:

ERRO[0016] Unable to decode event: unexpected end of JSON input

There are two issues involved, one read issue and one write issue:

• Read issue: default limit (65536B) on how much from log entry is read.
  Longer entries are truncated breaking JSON parsing.

• Write issue: SELinux prevents from writing long entries to journald.

This became especially severe after #15633 .
After the change the wait call for next-exit will hang indefinitely, because the exit event is not read.

/kind bug

related to:

• fix: event read from syslog when syslog entry too long #16781
• Allow containers to mount tmpfs_t file systems container-selinux#196