From f0c76f8a7b37bc47c5c07a92735b91e77e9124f1 Mon Sep 17 00:00:00 2001
From: Rob Norris <rob.norris@klarasystems.com>
Date: Tue, 14 Oct 2025 04:55:03 +1100
Subject: [PATCH] libzpool/cmn_err: remove suppression, add stop option,
 cleanup

A small uplift of the cmn_err() and panic() calls in userspace:

- remove the suppression on CE_NOTE. We have very few of these calls in
  a standard build, it's convenient for "print debugging".

- make prefixes clear and consistent.

- add LIBZPOOL_PANIC_STOP environment variable to send SIGSTOP to the
  process group on a panic, rather than abort(), so all threads remain
  alive for inspection.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #17834
---
 lib/libzpool/kernel.c | 79 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 60 insertions(+), 19 deletions(-)

diff --git a/lib/libzpool/kernel.c b/lib/libzpool/kernel.c
index 8ed374627..70eba5099 100644
--- a/lib/libzpool/kernel.c
+++ b/lib/libzpool/kernel.c
@@ -23,6 +23,7 @@
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2012, 2018 by Delphix. All rights reserved.
  * Copyright (c) 2016 Actifio, Inc. All rights reserved.
+ * Copyright (c) 2025, Klara, Inc.
  */
 
 #include <assert.h>
@@ -645,39 +646,60 @@ __dprintf(boolean_t dprint, const char *file, const char *func,
  * cmn_err() and panic()
  * =========================================================================
  */
-static char ce_prefix[CE_IGNORE][10] = { "", "NOTICE: ", "WARNING: ", "" };
-static char ce_suffix[CE_IGNORE][2] = { "", "\n", "\n", "" };
 
-__attribute__((noreturn)) void
-vpanic(const char *fmt, va_list adx)
+static __attribute__((noreturn)) void
+panic_stop_or_abort(void)
 {
-	(void) fprintf(stderr, "error: ");
-	(void) vfprintf(stderr, fmt, adx);
-	(void) fprintf(stderr, "\n");
+	const char *stopenv = getenv("LIBZPOOL_PANIC_STOP");
+	if (stopenv != NULL && atoi(stopenv)) {
+		fputs("libzpool: LIBZPOOL_PANIC_STOP is set, sending "
+		    "SIGSTOP to process group\n", stderr);
+		fflush(stderr);
+
+		kill(0, SIGSTOP);
+
+		fputs("libzpool: continued after panic stop, "
+		    "aborting\n", stderr);
+	}
 
 	abort();	/* think of it as a "user-level crash dump" */
 }
 
-__attribute__((noreturn)) void
-panic(const char *fmt, ...)
+static void
+vcmn_msg(int ce, const char *fmt, va_list adx)
 {
-	va_list adx;
+	switch (ce) {
+	case CE_IGNORE:
+		return;
+	case CE_CONT:
+		break;
+	case CE_NOTE:
+		fputs("libzpool: NOTICE: ", stderr);
+		break;
+	case CE_WARN:
+		fputs("libzpool: WARNING: ", stderr);
+		break;
+	case CE_PANIC:
+		fputs("libzpool: PANIC: ", stderr);
+		break;
+	default:
+		fputs("libzpool: [unknown severity %d]: ", stderr);
+		break;
+	}
 
-	va_start(adx, fmt);
-	vpanic(fmt, adx);
-	va_end(adx);
+	vfprintf(stderr, fmt, adx);
+	if (ce != CE_CONT)
+		fputc('\n', stderr);
+	fflush(stderr);
 }
 
 void
 vcmn_err(int ce, const char *fmt, va_list adx)
 {
+	vcmn_msg(ce, fmt, adx);
+
 	if (ce == CE_PANIC)
-		vpanic(fmt, adx);
-	if (ce != CE_NOTE) {	/* suppress noise in userland stress testing */
-		(void) fprintf(stderr, "%s", ce_prefix[ce]);
-		(void) vfprintf(stderr, fmt, adx);
-		(void) fprintf(stderr, "%s", ce_suffix[ce]);
-	}
+		panic_stop_or_abort();
 }
 
 void
@@ -690,6 +712,25 @@ cmn_err(int ce, const char *fmt, ...)
 	va_end(adx);
 }
 
+__attribute__((noreturn)) void
+panic(const char *fmt, ...)
+{
+	va_list adx;
+
+	va_start(adx, fmt);
+	vcmn_msg(CE_PANIC, fmt, adx);
+	va_end(adx);
+
+	panic_stop_or_abort();
+}
+
+__attribute__((noreturn)) void
+vpanic(const char *fmt, va_list adx)
+{
+	vcmn_msg(CE_PANIC, fmt, adx);
+	panic_stop_or_abort();
+}
+
 /*
  * =========================================================================
  * misc routines