On 10/20/22 01:16, Greg Kurz wrote:
When QEMU is started with `-daemonize`, all stdio descriptors get
redirected to `/dev/null`. This basically means that anything
printed with error_report() and friends is lost.
One could hope that passing `-D ${logfile}` would cause the messages
to go to `${logfile}`, as the documentation tends to suggest:
-D logfile
Output log in logfile instead of to stderr
Unfortunately, `-D` belongs to the logging framework and it only
does this redirection if some log item is also enabled with `-d`
or if QEMU was configured with `--enable-trace-backend=log`. A
typical production setup doesn't do tracing or fine-grain
debugging but it certainly needs to collect errors.
Ignore the check on enabled log items when QEMU is daemonized. Previous
behaviour is retained for the non-daemonized case. The logic is unrolled
as an `if` for better readability. Since qemu_set_log_internal() caches
the final log level and the per-thread property in global variables, it
seems more correct to check these instead of intermediary local variables.
Special care is needed for the `-D ${logfile} -d tid` case : `${logfile}`
is expected to be a template that contains exactly one `%d` that should be
expanded to a PID or TID. The logic in qemu_log_trylock() already takes
care of that for per-thread logs. Do it as well for the QEMU main thread
when opening the file.
I don't understand why daemonize changes -d tid at all.
If there's a bug there, please separate it out.
I don't understand the is_main_log_thread checks.
Why is the main thread special?
- /*
- * In all cases we only log if qemu_loglevel is set.
- * Also:
- * If per-thread, open the file for each thread in qemu_log_lock.
- * If not daemonized we will always log either to stderr
- * or to a file (if there is a filename).
- * If we are daemonized, we will only log if there is a filename.
- */
daemonized = is_daemonized();
- need_to_open_file = log_flags && !per_thread && (!daemonized || filename);
+ need_to_open_file = false;
+ if (!daemonized) {
+ /*
+ * If not daemonized we only log if qemu_loglevel is set, either to
+ * stderr or to a file (if there is a filename).
+ * If per-thread, open the file for each thread in qemu_log_trylock().
+ */
+ need_to_open_file = qemu_loglevel && !log_per_thread;
+ } else {
+ /*
+ * If we are daemonized, we will only log if there is a filename.
+ */
+ need_to_open_file = filename != NULL;
+ }
I would have thought that this was the only change required -- ignoring qemu_loglevel when
daemonized.
r~
