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.
Note that qemu_log_trylock() now must ensure that the main QEMU thread
only uses the global log file ; qemu_log_unlock() must be adapted as well
by checking thread_file which is always equal to NULL for the main thread.
Signed-off-by: Greg Kurz <gr...@kaod.org>
---
util/log.c | 49 ++++++++++++++++++++++++++++++++++++-------------
1 file changed, 36 insertions(+), 13 deletions(-)
diff --git a/util/log.c b/util/log.c
index e1c2535cfcd2..0fa23729c78c 100644
--- a/util/log.c
+++ b/util/log.c
@@ -82,6 +82,11 @@ static int log_thread_id(void)
#endif
}
+static bool is_main_log_thread(void)
+{
+ return log_thread_id() == getpid();
+}
+
/* Lock/unlock output. */
FILE *qemu_log_trylock(void)
@@ -90,7 +95,8 @@ FILE *qemu_log_trylock(void)
logfile = thread_file;
if (!logfile) {
- if (log_per_thread) {
+ /* Main thread to use the global file only */
+ if (log_per_thread && !is_main_log_thread()) {
g_autofree char *filename
= g_strdup_printf(global_filename, log_thread_id());
logfile = fopen(filename, "w");
@@ -124,7 +130,7 @@ void qemu_log_unlock(FILE *logfile)
if (logfile) {
fflush(logfile);
qemu_funlockfile(logfile);
- if (!log_per_thread) {
+ if (!thread_file) {
rcu_read_unlock();
}
}
@@ -253,16 +259,21 @@ static bool qemu_set_log_internal(const char *filename,
bool changed_name,
#endif
qemu_loglevel = log_flags;
- /*
- * 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;
+ }
if (logfile && (!need_to_open_file || changed_name)) {
qatomic_rcu_set(&global_file, NULL);
@@ -276,10 +287,22 @@ static bool qemu_set_log_internal(const char *filename,
bool changed_name,
if (!logfile && need_to_open_file) {
if (filename) {
- logfile = fopen(filename, log_append ? "a" : "w");
+ g_autofree char *fname = NULL;
+
+ /*
+ * If per-thread, filename contains a single %d that should be
+ * converted.
+ */
+ if (per_thread) {
+ fname = g_strdup_printf(filename, getpid());
+ } else {
+ fname = g_strdup(filename);
+ }
+
+ logfile = fopen(fname, log_append ? "a" : "w");
if (!logfile) {
error_setg_errno(errp, errno, "Error opening logfile %s",
- filename);
+ fname);
return false;
}
/* In case we are a daemon redirect stderr to logfile */
--
2.37.3
