https://github.com/openzfs/zfs/issues/15241
https://github.com/openzfs/zfs/pull/15560

From e0a7ec29d91b79adfd81073f229241351ed0ae21 Mon Sep 17 00:00:00 2001
From: Ilkka Sovanto <github@ilkka.kapsi.fi>
Date: Wed, 22 Nov 2023 20:24:47 +0200
Subject: [PATCH] Fix zoneid when USER_NS is disabled

getzoneid() should return GLOBAL_ZONEID instead of 0 when USER_NS is disabled.

Signed-off-by: Ilkka Sovanto <github@ilkka.kapsi.fi>
--- a/lib/libspl/os/linux/zone.c
+++ b/lib/libspl/os/linux/zone.c
@@ -42,20 +42,20 @@ getzoneid(void)
 	int c = snprintf(path, sizeof (path), "/proc/self/ns/user");
 	/* This API doesn't have any error checking... */
 	if (c < 0 || c >= sizeof (path))
-		return (0);
+		return (GLOBAL_ZONEID);
 
 	ssize_t r = readlink(path, buf, sizeof (buf) - 1);
 	if (r < 0)
-		return (0);
+		return (GLOBAL_ZONEID);
 
 	cp = strchr(buf, '[');
 	if (cp == NULL)
-		return (0);
+		return (GLOBAL_ZONEID);
 	cp++;
 
 	unsigned long n = strtoul(cp, NULL, 10);
 	if (n == ULONG_MAX && errno == ERANGE)
-		return (0);
+		return (GLOBAL_ZONEID);
 	zoneid_t z = (zoneid_t)n;
 
 	return (z);