Change in libosmocore[master]: logging: Change stderr + file target to use non-blocking write

[laforge]

Hello Jenkins Builder, pespin, 

I'd like you to reexamine a change. Please visit

    https://gerrit.osmocom.org/c/libosmocore/+/20296

to look at the new patch set (#15).

Change subject: logging: Change stderr + file target to use non-blocking write
......................................................................

logging: Change stderr + file target to use non-blocking write

So far, we used blocking, buffered fwrite() to write to stderr
and file targets.  This causes problems if there are [slow] consumers
causing delays, such as gnome-terminal (when the program is started
interactively) or systemd/journald (where we observe 64..128ms blocks on
stderr).

This patch introduces stderr/file based logging via write_queue
and osmo_select_main(), i.e. switch from glibc-buffered, blocking
to internally buffered, non-blocking writes.

* when osmo_stderr_target is created via application.c, we create it
  in blocking stream mode for backwards compatibility, particularly
  for [smaller] programs that don't use osmo_select_main()

* when the VTY code encounters 'log stderr' or 'log file FILENAME',
  we switch that respective target to non-blocking write-queue mode,
  as this means the application is in fact using osmo_select_main()

* The config file can now state 'log stderr blocking-io' or
  'log file FILENAME blocking-io' to explicitly enforce using blocking
  stream based I/O

* The application can at any time use API functions to switch either way

Closes: OS#4311
Change-Id: Ia58fd78535c41b3da3aeb7733aadc785ace610da
---
M include/osmocom/core/logging.h
M src/logging.c
M src/vty/logging_vty.c
M tests/logging/logging_vty_test.c
4 files changed, 314 insertions(+), 22 deletions(-)


  git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/96/20296/15
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Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Change-Id: Ia58fd78535c41b3da3aeb7733aadc785ace610da
Gerrit-Change-Number: 20296
Gerrit-PatchSet: 15
Gerrit-Owner: laforge <laforge at osmocom.org>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: laforge <laforge at osmocom.org>
Gerrit-Reviewer: pespin <pespin at sysmocom.de>
Gerrit-MessageType: newpatchset
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