Add option for forcible unmounting dataset while receiving snapshot.

Currently when the dataset is in use we can't receive snapshots.

    zfs send test/1@asd | zfs recv -FM test/2
    cannot unmount '/test/2': Device busy

This commits add option 'M' which attempts to forcibly unmount the
dataset.  Thanks to this we can enforce receiving snapshots in a
single step.

Note that this functionality is not supported on Linux because the
VFS will prevent active mounted filesystems from being unmounted,
even with the force option.  This is the intended VFS behavior.

Test cases were added to verify the expected behavior based on
the platform.

Discussed-with: Pawel Jakub Dawidek <pjd@FreeBSD.org>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Allan Jude <allanjude@freebsd.org>
External-issue: https://reviews.freebsd.org/D22306
Closes #9904

cmd/zfs/zfs_main.c

@@ -298,10 +298,10 @@ get_usage(zfs_help_t idx)
 	case HELP_PROMOTE:
 		return (gettext("\tpromote <clone-filesystem>\n"));
 	case HELP_RECEIVE:
-		return (gettext("\treceive [-vnsFhu] "
+		return (gettext("\treceive [-vMnsFhu] "
 		    "[-o <property>=<value>] ... [-x <property>] ...\n"
 		    "\t    <filesystem|volume|snapshot>\n"
-		    "\treceive [-vnsFhu] [-o <property>=<value>] ... "
+		    "\treceive [-vMnsFhu] [-o <property>=<value>] ... "
 		    "[-x <property>] ... \n"
 		    "\t    [-d | -e] <filesystem>\n"
 		    "\treceive -A <filesystem|volume>\n"));
@@ -4552,7 +4552,7 @@ zfs_do_receive(int argc, char **argv)
 		nomem();
 
 	/* check options */
-	while ((c = getopt(argc, argv, ":o:x:dehnuvFsA")) != -1) {
+	while ((c = getopt(argc, argv, ":o:x:dehMnuvFsA")) != -1) {
 		switch (c) {
 		case 'o':
 			if (!parseprop(props, optarg)) {
@@ -4587,6 +4587,9 @@ zfs_do_receive(int argc, char **argv)
 		case 'h':
 			flags.skipholds = B_TRUE;
 			break;
+		case 'M':
+			flags.forceunmount = B_TRUE;
+			break;
 		case 'n':
 			flags.dryrun = B_TRUE;
 			break;

include/libzfs.h

@@ -758,6 +758,9 @@ typedef struct recvflags {
 
 	/* mount the filesystem unless nomount is specified */
 	boolean_t domount;
+
+	/* force unmount while recv snapshot (private) */
+	boolean_t forceunmount;
 } recvflags_t;
 
 extern int zfs_receive(libzfs_handle_t *, const char *, nvlist_t *,

lib/libzfs/libzfs_sendrecv.c

@@ -4059,7 +4059,8 @@ zfs_receive_package(libzfs_handle_t *hdl, int fd, const char *destname,
 				    ZFS_TYPE_FILESYSTEM);
 				if (zhp != NULL) {
 					clp = changelist_gather(zhp,
-					    ZFS_PROP_MOUNTPOINT, 0, 0);
+					    ZFS_PROP_MOUNTPOINT, 0,
+					    flags->forceunmount ? MS_FORCE : 0);
 					zfs_close(zhp);
 					if (clp != NULL) {
 						softerr |=
@@ -4876,7 +4877,8 @@ zfs_receive_one(libzfs_handle_t *hdl, int infd, const char *tosnap,
 		if (!flags->dryrun && zhp->zfs_type == ZFS_TYPE_FILESYSTEM &&
 		    stream_wantsnewfs) {
 			/* We can't do online recv in this case */
-			clp = changelist_gather(zhp, ZFS_PROP_NAME, 0, 0);
+			clp = changelist_gather(zhp, ZFS_PROP_NAME, 0,
+			    flags->forceunmount ? MS_FORCE : 0);
 			if (clp == NULL) {
 				zfs_close(zhp);
 				err = -1;
@@ -5556,7 +5558,8 @@ zfs_receive(libzfs_handle_t *hdl, const char *tosnap, nvlist_t *props,
 			}
 
 			clp = changelist_gather(zhp, ZFS_PROP_MOUNTPOINT,
-			    CL_GATHER_MOUNT_ALWAYS, 0);
+			    CL_GATHER_MOUNT_ALWAYS,
+			    flags->forceunmount ? MS_FORCE : 0);
 			zfs_close(zhp);
 			if (clp == NULL) {
 				err = -1;

man/man8/zfs-receive.8

@@ -30,7 +30,7 @@
 .\" Copyright 2018 Nexenta Systems, Inc.
 .\" Copyright 2019 Joyent, Inc.
 .\"
-.Dd June 30, 2019
+.Dd February 16, 2020
 .Dt ZFS-RECEIVE 8
 .Os Linux
 .Sh NAME
@@ -39,14 +39,14 @@
 .Sh SYNOPSIS
 .Nm
 .Cm receive
-.Op Fl Fhnsuv
+.Op Fl FhMnsuv
 .Op Fl o Sy origin Ns = Ns Ar snapshot
 .Op Fl o Ar property Ns = Ns Ar value
 .Op Fl x Ar property
 .Ar filesystem Ns | Ns Ar volume Ns | Ns Ar snapshot
 .Nm
 .Cm receive
-.Op Fl Fhnsuv
+.Op Fl FhMnsuv
 .Op Fl d Ns | Ns Fl e
 .Op Fl o Sy origin Ns = Ns Ar snapshot
 .Op Fl o Ar property Ns = Ns Ar value
@@ -61,7 +61,7 @@
 .It Xo
 .Nm
 .Cm receive
-.Op Fl Fhnsuv
+.Op Fl FhMnsuv
 .Op Fl o Sy origin Ns = Ns Ar snapshot
 .Op Fl o Ar property Ns = Ns Ar value
 .Op Fl x Ar property
@@ -70,7 +70,7 @@
 .It Xo
 .Nm
 .Cm receive
-.Op Fl Fhnsuv
+.Op Fl FhMnsuv
 .Op Fl d Ns | Ns Fl e
 .Op Fl o Sy origin Ns = Ns Ar snapshot
 .Op Fl o Ar property Ns = Ns Ar value
@@ -229,6 +229,9 @@ that element to determine the name of the target file system for the new
 snapshot as described in the paragraph above.
 .It Fl h
 Skip the receive of holds.  There is no effect if holds are not sent.
+.It Fl M
+Force an unmount of the file system while receiving a snapshot.
+This option is not supported on Linux.
 .It Fl n
 Do not actually receive the stream.
 This can be useful in conjunction with the

tests/runfiles/common.run

@@ -208,9 +208,10 @@ tests = ['zfs_receive_001_pos', 'zfs_receive_002_pos', 'zfs_receive_003_pos',
     'zfs_receive_007_neg', 'zfs_receive_008_pos', 'zfs_receive_009_neg',
     'zfs_receive_010_pos', 'zfs_receive_011_pos', 'zfs_receive_012_pos',
     'zfs_receive_013_pos', 'zfs_receive_014_pos', 'zfs_receive_015_pos',
-    'receive-o-x_props_override', 'zfs_receive_from_encrypted',
+    'zfs_receive_016_pos', 'receive-o-x_props_override',
-    'zfs_receive_to_encrypted', 'zfs_receive_raw',
+    'zfs_receive_from_encrypted', 'zfs_receive_to_encrypted',
-    'zfs_receive_raw_incremental', 'zfs_receive_-e', 'zfs_receive_raw_-d']
+    'zfs_receive_raw', 'zfs_receive_raw_incremental', 'zfs_receive_-e',
+    'zfs_receive_raw_-d']
 tags = ['functional', 'cli_root', 'zfs_receive']
 
 [tests/functional/cli_root/zfs_rename]

tests/zfs-tests/tests/functional/cli_root/zfs_receive/Makefile.am

@@ -17,6 +17,7 @@ dist_pkgdata_SCRIPTS = \
 	zfs_receive_013_pos.ksh \
 	zfs_receive_014_pos.ksh \
 	zfs_receive_015_pos.ksh \
+	zfs_receive_016_pos.ksh \
 	receive-o-x_props_override.ksh \
 	zfs_receive_from_encrypted.ksh \
 	zfs_receive_to_encrypted.ksh \

tests/zfs-tests/tests/functional/cli_root/zfs_receive/zfs_receive_016_pos.ksh

@@ -0,0 +1,85 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+# Copyright (c) 2020 by Mariusz Zaborski <oshogbo@FreeBSD.org>.
+
+#
+# DESCRIPTION:
+# Verify 'zfs recv' can forcibly unmount filesystem while receiving
+# stream.
+#
+# STRATEGY:
+# 1. Create snapshot of file system
+# 2. Make a zfs filesystem mountpoint busy
+# 3. Receive filesystem with force flag.
+# 4. Verify that stream was received or failed on Linux.
+#
+
+. $STF_SUITE/tests/functional/cli_root/cli_common.kshlib
+
+verify_runnable "both"
+
+function cleanup
+{
+	cd $curpath
+
+	for snap in $init_snap $rst_snap; do
+                snapexists $snap && \
+                        destroy_snapshot $snap
+        done
+
+	datasetexists $rst_root && \
+		destroy_dataset $rst_root
+
+	for file in $full_bkup
+	do
+		[[ -e $file ]] && \
+			log_must rm -f $file
+	done
+
+	[[ -d $TESTDIR1 ]] && \
+		log_must rm -rf $TESTDIR1
+}
+
+log_assert "Verify 'zfs recv' can forcibly unmount busy filesystem."
+log_onexit cleanup
+
+curpath=`dirname $0`
+init_snap=$TESTPOOL/$TESTFS@init_snap
+full_bkup=$TEST_BASE_DIR/fullbkup.$$
+rst_root=$TESTPOOL/rst_ctr
+rst_snap=$rst_root@init_snap
+
+log_note "Verify 'zfs recv' can forcible unmount busy filesystem."
+
+# Preparation
+log_must zfs create $rst_root
+[[ ! -d $TESTDIR1 ]] && \
+	log_must mkdir -p $TESTDIR1
+log_must zfs set mountpoint=$TESTDIR1 $rst_root
+
+log_must zfs snapshot $init_snap
+log_must eval "zfs send $init_snap > $full_bkup"
+
+# Test
+log_must cd $TESTDIR1
+if is_linux; then
+    # Linux does not support it.
+    log_mustnot zfs receive -MF $rst_snap < $full_bkup
+else
+    log_must zfs receive -MF $rst_snap < $full_bkup
+fi
+
+log_pass "The busy filesystem was unmounted or busy as expected."