logd: wakeup wrap timeout if realtime changes drastically
--wrap flag in logcat translates directly to the mTimeout inside logd,
the value set is ANDROID_LOG_WRAP_DEFAULT_TIMEOUT defined in
<log/log_read.h> as 7200 or 2 hours. For a non blocking read with
a selected timeout, the logger waits until either the log buffer is
about to 'wrap' and prune the log entry, or at the specified timeout.
Non blocking in the logger context means that when there are no more
log entries, the socket is closed.
clock_gettime(CLOCK_REALTIME) is UTC 1970 epoch *NIX time. Is only
affected for time updates, not timezone or daylight savings time.
If there is a large user initiated time change, both the log entries
and the timeout mentioned above really get called into question, so we
trigger a release of the logs for clarity. This is so that the log
reader can handle the disruptively updated time, and can immediately
check the local time if necessary.
The logger has a 5 second window for entries to land in time sorted
order into the logging list. This should offer the log reader some
differentiation between logging order sequence for monotonically
increasing time, and sequence order in the face of user initiated time
adjustments that break monotonicity.
This change is about major time adjustments that can cause Fear,
Uncertainty or Doubt about log entries. By returning, immediate action
can be taken, rather than having to comb through the logs with less
details about the time disruptions in hand. The least it can do is
record what we have, and restart the call with a new tail time and
timeout.
Test: gTest liblog-unit-tests logcat-unit-test logd-unit-tests
Bug: 35373582
Change-Id: I92cac83be99d68634ffd4ebd2f3a3067cfd0e942
1 file changed