From 0635fe29225b5a4ecac63fc9d95dff63517d0003 Mon Sep 17 00:00:00 2001
From: Kyle Evans <kevans@FreeBSD.org>
Date: Sun, 20 Apr 2025 22:47:59 -0500
Subject: [PATCH] libbe: attempt to remove autocreated mountpoints at unmount
 time

We use a be_mount.XXXX pattern to mkdtemp(3) when creating these, which
seems reasonably unique enough to just continue using that.  Record the
mountpoint of the root dataset and check the dirname of that for the
auto-creation trait.  There's no sense in this bubbling up an error to
callers, so we'll just ignore an error for now.

Requested by:	manu

(cherry picked from commit d6fbae084a2a0e07805633ca46935963357f1efa)
---
 lib/libbe/be_access.c | 30 +++++++++++++++++++++++++++++-
 lib/libbe/libbe.3     |  7 +++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/lib/libbe/be_access.c b/lib/libbe/be_access.c
index 67b30d3fb4f..51f5a75e957 100644
--- a/lib/libbe/be_access.c
+++ b/lib/libbe/be_access.c
@@ -33,6 +33,8 @@
 #include "be.h"
 #include "be_impl.h"
 
+#define	LIBBE_MOUNT_PREFIX	"be_mount."	/* XXX */
+
 struct be_mountcheck_info {
 	const char *path;
 	char *name;
@@ -164,7 +166,11 @@ be_umount_iter(zfs_handle_t *zfs_hdl, void *data)
 	if (!zfs_is_mounted(zfs_hdl, &mountpoint)) {
 		return (0);
 	}
-	free(mountpoint);
+
+	if (info->depth == 0 && info->mountpoint == NULL)
+		info->mountpoint = mountpoint;
+	else
+		free(mountpoint);
 
 	if (zfs_unmount(zfs_hdl, NULL, info->mntflags) != 0) {
 		switch (errno) {
@@ -307,10 +313,32 @@ be_unmount(libbe_handle_t *lbh, const char *bootenv, int flags)
 	info.depth = 0;
 
 	if ((err = be_umount_iter(root_hdl, &info)) != 0) {
+		free(__DECONST(char *, info.mountpoint));
 		zfs_close(root_hdl);
 		return (err);
 	}
 
+	/*
+	 * We'll attempt to remove the directory if we created it on a
+	 * best-effort basis.  rmdir(2) failure will not be reported.
+	 */
+	if (info.mountpoint != NULL) {
+		const char *mdir;
+
+		mdir = strrchr(info.mountpoint, '/');
+		if (mdir == NULL)
+			mdir = info.mountpoint;
+		else
+			mdir++;
+
+		if (strncmp(mdir, LIBBE_MOUNT_PREFIX,
+		    sizeof(LIBBE_MOUNT_PREFIX) - 1) == 0) {
+			(void)rmdir(info.mountpoint);
+		}
+	}
+
+	free(__DECONST(char *, info.mountpoint));
+
 	zfs_close(root_hdl);
 	return (BE_ERR_SUCCESS);
 }
diff --git a/lib/libbe/libbe.3 b/lib/libbe/libbe.3
index 644b1d71ccd..743922a7639 100644
--- a/lib/libbe/libbe.3
+++ b/lib/libbe/libbe.3
@@ -392,6 +392,13 @@ This list of properties matches the properties collected by
 The
 .Fn be_unmount
 function will unmount the given boot environment.
+If the mount point looks like it was created by
+.Fn be_mount ,
+then
+.Fn be_unmount
+will attempt to
+.Xr rmdir 2
+the mountpoint after a successful unmount.
 Setting the
 .Dv BE_MNT_FORCE
 flag will pass