From b9f5227d2bdd685baa1b84370a21bd4fb87132c5 Mon Sep 17 00:00:00 2001
From: Rob Norris <robn@despairlabs.com>
Date: Sat, 28 Dec 2024 15:27:26 +1100
Subject: [PATCH] lzc_ioctl_fd: add ZFS_IOC_TRACE envvar to enable ioctl
 tracing

When set, dumps all ZFS ioctl calls and returns and their nvlists to
STDERR, to make debugging and understanding a lot easier.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #17344
(cherry picked from commit a387b7599ce8d0786618893563c0ad3015f22595)
---
 lib/libzfs_core/libzfs_core.c | 38 ++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/lib/libzfs_core/libzfs_core.c b/lib/libzfs_core/libzfs_core.c
index 5958cd98d..9347aa7c6 100644
--- a/lib/libzfs_core/libzfs_core.c
+++ b/lib/libzfs_core/libzfs_core.c
@@ -102,6 +102,8 @@ static int g_fd = -1;
 static pthread_mutex_t g_lock = PTHREAD_MUTEX_INITIALIZER;
 static int g_refcount;
 
+static int g_ioc_trace = 0;
+
 #ifdef ZFS_DEBUG
 static zfs_ioc_t fail_ioc_cmd = ZFS_IOC_LAST;
 static zfs_errno_t fail_ioc_err;
@@ -154,6 +156,10 @@ libzfs_core_init(void)
 #ifdef ZFS_DEBUG
 	libzfs_core_debug_ioc();
 #endif
+
+	if (getenv("ZFS_IOC_TRACE"))
+		g_ioc_trace = 1;
+
 	(void) pthread_mutex_unlock(&g_lock);
 	return (0);
 }
@@ -176,7 +182,37 @@ libzfs_core_fini(void)
 int
 lzc_ioctl_fd(int fd, unsigned long ioc, zfs_cmd_t *zc)
 {
-	return (lzc_ioctl_fd_os(fd, ioc, zc));
+	if (!g_ioc_trace)
+		return (lzc_ioctl_fd_os(fd, ioc, zc));
+
+	nvlist_t *nvl;
+
+	fprintf(stderr, "=== lzc_ioctl: call: ioc=0x%lx name=%s\n",
+	    ioc, zc->zc_name[0] ? zc->zc_name : "[none]");
+	if (zc->zc_nvlist_src) {
+		nvl = fnvlist_unpack(
+		    (void *)(uintptr_t)zc->zc_nvlist_src,
+		    zc->zc_nvlist_src_size);
+		nvlist_print(stderr, nvl);
+		fnvlist_free(nvl);
+	}
+
+	int rc = lzc_ioctl_fd_os(fd, ioc, zc);
+	int err = errno;
+
+	fprintf(stderr, "=== lzc_ioctl: result: ioc=0x%lx name=%s "
+	    "rc=%d errno=%d\n", ioc, zc->zc_name[0] ? zc->zc_name : "[none]",
+	    rc, (rc < 0 ? err : 0));
+	if (rc >= 0 && zc->zc_nvlist_dst) {
+		nvl = fnvlist_unpack(
+		    (void *)(uintptr_t)zc->zc_nvlist_dst,
+		    zc->zc_nvlist_dst_size);
+		nvlist_print(stderr, nvl);
+		fnvlist_free(nvl);
+	}
+
+	errno = err;
+	return (rc);
 }
 
 static int