Re: How to configure flushing klog by syslog

[RVP <rvp%SDF.ORG@localhost>]

> I am trying to use printf() in kernel module for debugging purposes and
> I cannot find how to force flushing klog by syslogd.
> I found syslogd option -S. Manual page says: "
> -S               Sync kernel messages to disk immediately.
>
> After adding to rc.conf: syslogd_flags="-S" nothing changes.

Looks like a missing wakeup, so reading from /dev/klog just waits until some
_other_ function chances to wake up the sleeper by calling logwakeup().

Can you try the patch below? If it works, then you can file a PR (I've done
only 2 and the other functions which use the TOLOG flag might need the same
treatment).

---START PATCH---
--- src/sys/kern/subr_prf.c.orig	2023-08-29 21:23:14.000000000 +0000
+++ src/sys/kern/subr_prf.c	2025-01-13 08:37:45.789743655 +0000
@@ -1059,6 +1059,9 @@
 	va_start(ap, fmt);
 	vprintf_flags(TOLOG, fmt, ap);
 	va_end(ap);
+
+	if (!panicstr)
+		logwakeup();
 }

 /*
@@ -1104,6 +1107,9 @@
 	va_start(ap, fmt);
 	vprintf_flags(TOCONS | TOLOG, fmt, ap);
 	va_end(ap);
+
+	if (!panicstr)
+		logwakeup();
 }

 /*
---END PATCH---

-RVP