bectl: Add -E flag to create an empty boot environment

Signed-off-by: Pat Maddox <pat@patmaddox.com>
Reviewed by:	kevans
MFC after:	1 week
Closes:		https://github.com/freebsd/freebsd-src/pull/1975

lib/libbe/be.c

@@ -891,6 +891,54 @@ be_create_from_existing(libbe_handle_t *lbh, const char *bename, const char *old
 	return (set_error(lbh, err));
 }
 
+/*
+ * Create a zfs dataset and map the return to libbe error.
+ */
+static int
+be_zfs_create(libzfs_handle_t *lzh, const char *buf, zfs_type_t t,
+    nvlist_t *props)
+{
+	int err;
+
+	if ((err = zfs_create(lzh, buf, t, props)) != 0) {
+		switch (err) {
+		case EZFS_EXISTS:
+			return (BE_ERR_EXISTS);
+		case EZFS_NOENT:
+			return (BE_ERR_NOENT);
+		case EZFS_BADTYPE:
+		case EZFS_BADVERSION:
+			return (BE_ERR_NOPOOL);
+		case EZFS_BADPROP:
+		default:
+			/* We set something up wrong, probably... */
+			return (BE_ERR_UNKNOWN);
+		}
+	}
+
+	return (BE_ERR_SUCCESS);
+}
+
+
+/*
+ * Create an empty boot environment.
+ */
+int
+be_create_empty(libbe_handle_t *lbh, const char *bename)
+{
+	char buf[BE_MAXPATHLEN];
+	int err;
+
+	if ((err = be_validate_name(lbh, bename)) != 0)
+		return (set_error(lbh, err));
+
+	if ((err = be_root_concat(lbh, bename, buf)) != 0)
+		return (set_error(lbh, err));
+
+	err = be_zfs_create(lbh->lzh, buf, ZFS_TYPE_FILESYSTEM, NULL);
+	return (set_error(lbh, err));
+}
+
 
 /*
  * Verifies that a snapshot has a valid name, exists, and has a mountpoint of
@@ -1118,21 +1166,9 @@ be_create_child_noent(libbe_handle_t *lbh, const char *active,
 	nvlist_add_string(props, "mountpoint", child_path);
 
 	/* Create */
-	if ((err = zfs_create(lbh->lzh, active, ZFS_TYPE_DATASET,
+	if ((err = be_zfs_create(lbh->lzh, active, ZFS_TYPE_DATASET,
 	    props)) != 0) {
-		switch (err) {
-		case EZFS_EXISTS:
-			return (set_error(lbh, BE_ERR_EXISTS));
-		case EZFS_NOENT:
-			return (set_error(lbh, BE_ERR_NOENT));
-		case EZFS_BADTYPE:
-		case EZFS_BADVERSION:
-			return (set_error(lbh, BE_ERR_NOPOOL));
-		case EZFS_BADPROP:
-		default:
-			/* We set something up wrong, probably... */
-			return (set_error(lbh, BE_ERR_UNKNOWN));
-		}
+		return (set_error(lbh, err));
 	}
 	nvlist_free(props);
 

lib/libbe/be.h

@@ -65,6 +65,7 @@ bool be_is_auto_snapshot_name(libbe_handle_t *, const char *);
 /* Bootenv creation functions */
 int be_create(libbe_handle_t *, const char *);
 int be_create_depth(libbe_handle_t *, const char *, const char *, int);
+int be_create_empty(libbe_handle_t *, const char *);
 int be_create_from_existing(libbe_handle_t *, const char *, const char *);
 int be_create_from_existing_snap(libbe_handle_t *, const char *, const char *);
 int be_snapshot(libbe_handle_t *, const char *, const char *, bool, char *);

lib/libbe/libbe.3

@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd December 11, 2025
+.Dd February 4, 2026
 .Dt LIBBE 3
 .Os
 .Sh NAME
@@ -69,6 +69,9 @@
 .Fn be_create_depth "libbe_handle_t *hdl" "const char *be_name" "const char *snap" "int depth"
 .Pp
 .Ft int
+.Fn be_create_empty "libbe_handle_t *hdl" "const char *be_name"
+.Pp
+.Ft int
 .Fn be_create_from_existing "libbe_handle_t *hdl" "const char *be_name" "const char *be_origin"
 .Pp
 .Ft int
@@ -282,6 +285,10 @@ A depth of '0' is no recursion and '-1' is unlimited (i.e., a recursive boot
 environment).
 .Pp
 The
+.Fn be_create_empty
+function creates an empty boot environment with the given name.
+.Pp
+The
 .Fn be_create_from_existing
 function creates a boot environment with the given name from the name of an
 existing boot environment.

lib/libbe/tests/Makefile

@@ -20,6 +20,6 @@ CFLAGS+= -I${ZFSTOP}/lib/libspl/include/os/freebsd
 CFLAGS+= -I${SRCTOP}/sys
 CFLAGS+= -I${SRCTOP}/cddl/compat/opensolaris/include
 CFLAGS+= -include ${ZFSTOP}/include/os/freebsd/spl/sys/ccompile.h
-CFLAGS+= -DHAVE_ISSETUGID 
+CFLAGS+= -DHAVE_ISSETUGID -DHAVE_STRLCAT -DHAVE_STRLCPY
 
 .include <bsd.test.mk>

lib/libbe/tests/be_create.sh

@@ -174,6 +174,15 @@ libbe_create_body()
 	# the child dataset should exist
 	atf_check -o not-empty \
 		  zfs list "${zpool}/ROOT/relative-snap/usr"
+
+	# test empty BE creation.
+	atf_check $prog "${zpool}/ROOT" \
+		empty \
+		ignored \
+		0
+	# the dataset should exist
+	atf_check -o not-empty \
+		zfs list "${zpool}/ROOT/empty"
 }
 
 libbe_create_cleanup()

lib/libbe/tests/target_prog.c

@@ -27,6 +27,7 @@
 
 #include <sys/cdefs.h>
 #include <be.h>
+#include <string.h>
 
 /*
  * argv[1] = root boot environment (e.g. zroot/ROOT),
@@ -36,15 +37,17 @@
  */
 int main(int argc, char *argv[]) {
 
-        libbe_handle_t *lbh;
+	libbe_handle_t *lbh;
 
 	if (argc != 5)
-		return -1;
+		return (-1);
 
-        if ((lbh = libbe_init(argv[1])) == NULL)
-                return -1;
+	if ((lbh = libbe_init(argv[1])) == NULL)
+		return (-1);
 
 	libbe_print_on_error(lbh, true);
 
+	if (strcmp(argv[2], "empty") == 0)
+		return (be_create_empty(lbh, argv[2]));
 	return (be_create_depth(lbh, argv[2], argv[3], atoi(argv[4])));
 }

sbin/bectl/bectl.8

@@ -3,7 +3,7 @@
 .\"
 .\" SPDX-License-Identifier: BSD-2-Clause
 .\"
-.Dd June 13, 2025
+.Dd February 4, 2026
 .Dt BECTL 8
 .Os
 .Sh NAME
@@ -33,6 +33,11 @@
 .Ar beName@snapshot
 .Nm
 .Op Fl r Ar beroot
+.Cm create
+.Fl E
+.Ar newBeName
+.Nm
+.Op Fl r Ar beroot
 .Cm destroy
 .Op Fl \&Fo
 .Ar beName Ns Op Cm @ Ns Ar snapshot
@@ -181,6 +186,13 @@ for a discussion on different layouts.
 .Pp
 No new boot environment is created with this subcommand.
 .It Xo
+.Cm create
+.Fl E
+.Ar newBeName
+.Xc
+Create a new empty boot environment named
+.Ar newBeName .
+.It Xo
 .Cm destroy
 .Op Fl \&Fo
 .Ar beName Ns Op Cm @ Ns Ar snapshot

sbin/bectl/bectl.c

@@ -53,6 +53,7 @@ usage(bool explicit)
 	    "\tbectl [-r beroot] check\n"
 	    "\tbectl [-r beroot] create [-r] [-e {nonActiveBe | beName@snapshot}] beName\n"
 	    "\tbectl [-r beroot] create [-r] beName@snapshot\n"
+	    "\tbectl [-r beroot] create -E beName\n"
 	    "\tbectl [-r beroot] destroy [-Fo] {beName | beName@snapshot}\n"
 	    "\tbectl [-r beroot] export sourceBe\n"
 	    "\tbectl [-r beroot] import targetBe\n"
@@ -184,15 +185,19 @@ bectl_cmd_create(int argc, char *argv[])
 	char snapshot[BE_MAXPATHLEN];
 	char *atpos, *bootenv, *snapname;
 	int err, opt;
-	bool recursive;
+	bool empty, recursive;
 
 	snapname = NULL;
+	empty = false;
 	recursive = false;
-	while ((opt = getopt(argc, argv, "e:r")) != -1) {
+	while ((opt = getopt(argc, argv, "e:Er")) != -1) {
 		switch (opt) {
 		case 'e':
 			snapname = optarg;
 			break;
+		case 'E':
+			empty = true;
+			break;
 		case 'r':
 			recursive = true;
 			break;
@@ -221,6 +226,13 @@ bectl_cmd_create(int argc, char *argv[])
 		 */
 		*atpos++ = '\0';
 		err = be_snapshot(be, bootenv, atpos, recursive, NULL);
+	} else if (empty) {
+		if (snapname || recursive) {
+			fprintf(stderr,
+			    "bectl create: -E cannot be combined with -e or -r\n");
+			return (usage(false));
+		}
+		err = be_create_empty(be, bootenv);
 	} else {
 		if (snapname == NULL)
 			/* Create from currently booted BE */

sbin/bectl/tests/bectl_test.sh

@@ -126,6 +126,14 @@ bectl_create_body()
 		zfs list "${zpool}/ROOT/recursive/usr"
 	atf_check -o not-empty \
 		zfs list "${zpool}/ROOT/recursive-snap/usr"
+
+	# Test creation of an empty BE.
+	atf_check bectl -r ${zpool}/ROOT create -E empty
+	atf_check -o inline:"-\n" zfs get -H -o value origin ${zpool}/ROOT/empty
+	atf_check -e match:"cannot be combined" -s not-exit:0 \
+		bectl -r ${zpool}/ROOT create -E -e not-allowed empty-existing
+	atf_check -e match:"cannot be combined" -s not-exit:0 \
+		bectl -r ${zpool}/ROOT create -E -r empty-recursive
 }
 bectl_create_cleanup()
 {