When QEMU is started with `--daemonize -D ${logfile} -d ${some_log_item}`,
error logs from error_report() and friends go to ${logfile}, but if QEMU
is started with `-daemonize -D ${logfile}` and no `-d`, the file isn't
even created and all logs go to /dev/null.

This inconsistency is quite confusing for users and gives the impression
that QEMU doesn't log errors at all. It seems much saner to always create
the log file when `-D` was passed and to be able to report errors.

It was spotted by the kata-containers project, which happens to do just
that `--daemonize -D` without `-d` trick. It is possible that they will
stop doing so and catch errors through QEMU's stderr at some point, but
I'm posting the patches anyway.

v2:
- new log_thread_id() implementation for hosts without gettid() syscall
- avoid conflict between global log file and per-thread logfile
- style improvements

Greg Kurz (2):
  util/log: Derive thread id from getpid() on hosts w/o gettid() syscall
  util/log: Always send errors to logfile when daemonized

 util/log.c | 56 ++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 42 insertions(+), 14 deletions(-)

-- 
2.37.3