systemd mount generator and tracking ZEDLET

zfs-mount-generator implements the "systemd generator" protocol,
producing systemd.mount units from the cached outputs of zfs list,
during early boot, integrating with systemd.

Each pool has an indpendent cache of the command

  zfs list -H -oname,mountpoint,canmount -tfilesystem -r $pool

which is kept synchronized by the ZEDLET

  history_event-zfs-list-cacher.sh

Datasets not in the cache will be loaded later in the boot process by
zfs-mount.service, including pools without a cache.

Among other things, this allows for complex mount hierarchies.

Reviewed-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Antonio Russo <antonio.e.russo@gmail.com>
Closes #7329

cmd/zed/Makefile.am

@@ -4,7 +4,8 @@ DEFAULT_INCLUDES += \
 	-I$(top_srcdir)/include \
 	-I$(top_srcdir)/lib/libspl/include
 
-EXTRA_DIST = zed.d/README
+EXTRA_DIST = zed.d/README \
+	zed.d/history_event-zfs-list-cacher.sh.in
 
 sbin_PROGRAMS = zed
 
@@ -60,6 +61,7 @@ dist_zedexec_SCRIPTS = \
 	zed.d/all-syslog.sh \
 	zed.d/data-notify.sh \
 	zed.d/generic-notify.sh \
+	zed.d/history_event-zfs-list-cacher.sh \
 	zed.d/resilver_finish-notify.sh \
 	zed.d/scrub_finish-notify.sh \
 	zed.d/statechange-led.sh \
@@ -69,6 +71,13 @@ dist_zedexec_SCRIPTS = \
 	zed.d/pool_import-led.sh \
 	zed.d/resilver_finish-start-scrub.sh
 
+zed.d/history_event-zfs-list-cacher.sh: %: %.in
+	-$(SED) -e 's,@bindir\@,$(bindir),g' \
+		-e 's,@runstatedir\@,$(runstatedir),g' \
+		-e 's,@sbindir\@,$(sbindir),g' \
+		-e 's,@sysconfdir\@,$(sysconfdir),g' \
+		$< >'$@'
+
 zedconfdefaults = \
 	all-syslog.sh \
 	data-notify.sh \

cmd/zed/zed.d/.gitignore

@@ -0,0 +1 @@
+history_event-zfs-list-cacher.sh

cmd/zed/zed.d/history_event-zfs-list-cacher.sh.in

@@ -0,0 +1,73 @@
+#!/bin/sh
+#
+# Track changes to enumerated pools for use in early-boot
+set -ef
+
+FSLIST_DIR="@sysconfdir@/zfs/zfs-list.cache"
+FSLIST_TMP="@runstatedir@/zfs-list.cache.new"
+FSLIST="${FSLIST_DIR}/${ZEVENT_POOL}"
+
+# If the pool specific cache file is not writeable, abort
+[ -w "${FSLIST}" ] || exit 0
+
+[ -f "${ZED_ZEDLET_DIR}/zed.rc" ] && . "${ZED_ZEDLET_DIR}/zed.rc"
+. "${ZED_ZEDLET_DIR}/zed-functions.sh"
+
+zed_exit_if_ignoring_this_event
+zed_check_cmd "${ZFS}" sort diff grep
+
+# If we are acting on a snapshot, we have nothing to do
+printf '%s' "${ZEVENT_HISTORY_DSNAME}" | grep '@' && exit 0
+
+# We obtain a lock on zfs-list to avoid any simultaneous writes.
+# If we run into trouble, log and drop the lock
+abort_alter() {
+  zed_log_msg "Error updating zfs-list.cache!"
+  zed_unlock zfs-list
+}
+
+finished() {
+  zed_unlock zfs-list
+  trap - EXIT
+  exit 0
+}
+
+case "${ZEVENT_HISTORY_INTERNAL_NAME}" in
+    create|"finish receiving"|import|destroy|rename)
+      ;;
+
+    export)
+        zed_lock zfs-list
+        trap abort_alter EXIT
+        echo > "${FSLIST}"
+        finished
+      ;;
+
+    set|inherit)
+        # Only act if the mountpoint or canmount setting is altered.
+        case "${ZEVENT_HISTORY_INTERNAL_STR}" in
+            canmount=*|mountpoint=*) ;;
+            *) exit 0 ;;
+        esac
+      ;;
+
+    *)
+        # Ignore all other events.
+        exit 0
+      ;;
+esac
+
+zed_lock zfs-list
+trap abort_alter EXIT
+
+"${ZFS}" list -H -tfilesystem -oname,mountpoint,canmount -r "${ZEVENT_POOL}" \
+    >"${FSLIST_TMP}"
+
+# Sort the output so that it is stable
+sort "${FSLIST_TMP}" -o "${FSLIST_TMP}"
+
+# Don't modify the file if it hasn't changed
+diff -q "${FSLIST_TMP}" "${FSLIST}" || mv "${FSLIST_TMP}" "${FSLIST}"
+rm -f "${FSLIST_TMP}"
+
+finished

config/user-systemd.m4

@@ -20,6 +20,11 @@ AC_DEFUN([ZFS_AC_CONFIG_USER_SYSTEMD], [
 		[install systemd module load files into dir [[/usr/lib/modules-load.d]]]),
 		systemdmoduleloaddir=$withval,systemdmodulesloaddir=/usr/lib/modules-load.d)
 
+	AC_ARG_WITH(systemdgeneratordir,
+		AC_HELP_STRING([--with-systemdgeneratordir=DIR],
+		[install systemd generators in dir [[/usr/lib/systemd/system-generators]]]),
+		systemdgeneratordir=$withval,systemdgeneratordir=/usr/lib/systemd/system-generators)
+
 	AS_IF([test "x$enable_systemd" = xcheck], [
 		AS_IF([systemctl --version >/dev/null 2>&1],
 			[enable_systemd=yes],
@@ -32,7 +37,7 @@ AC_DEFUN([ZFS_AC_CONFIG_USER_SYSTEMD], [
 	AS_IF([test "x$enable_systemd" = xyes], [
 		ZFS_INIT_SYSTEMD=systemd
 		ZFS_MODULE_LOAD=modules-load.d
-		DEFINE_SYSTEMD='--with systemd --define "_unitdir $(systemdunitdir)" --define "_presetdir $(systemdpresetdir)"'
+		DEFINE_SYSTEMD='--with systemd --define "_unitdir $(systemdunitdir)" --define "_presetdir $(systemdpresetdir)" --define "_generatordir $(systemdgeneratordir)"'
 		modulesloaddir=$systemdmodulesloaddir
 	],[
 		DEFINE_SYSTEMD='--without systemd'
@@ -43,5 +48,6 @@ AC_DEFUN([ZFS_AC_CONFIG_USER_SYSTEMD], [
 	AC_SUBST(DEFINE_SYSTEMD)
 	AC_SUBST(systemdunitdir)
 	AC_SUBST(systemdpresetdir)
+	AC_SUBST(systemdgeneratordir)
 	AC_SUBST(modulesloaddir)
 ])

configure.ac

@@ -67,6 +67,7 @@ AC_CONFIG_FILES([
 	etc/zfs/Makefile
 	etc/systemd/Makefile
 	etc/systemd/system/Makefile
+	etc/systemd/system-generators/Makefile
 	etc/sudoers.d/Makefile
 	etc/modules-load.d/Makefile
 	man/Makefile

etc/systemd/Makefile.am

@@ -1 +1 @@
-SUBDIRS = system
+SUBDIRS = system system-generators

etc/systemd/system-generators/.gitignore

@@ -0,0 +1 @@
+zfs-mount-generator

etc/systemd/system-generators/Makefile.am

@@ -0,0 +1,15 @@
+systemdgenerator_SCRIPTS = \
+	zfs-mount-generator
+
+EXTRA_DIST = \
+	$(top_srcdir)/etc/systemd/system-generators/zfs-mount-generator.in
+
+$(systemdgenerator_SCRIPTS): %: %.in
+	-$(SED) -e 's,@bindir\@,$(bindir),g' \
+		-e 's,@runstatedir\@,$(runstatedir),g' \
+		-e 's,@sbindir\@,$(sbindir),g' \
+		-e 's,@sysconfdir\@,$(sysconfdir),g' \
+		$< >'$@'
+
+distclean-local::
+	-$(RM) $(systemdgenerator_SCRIPTS)

etc/systemd/system-generators/zfs-mount-generator.in

@@ -0,0 +1,115 @@
+#!/bin/sh
+
+# zfs-mount-generator - generates systemd mount units for zfs
+# Copyright (c) 2017 Antonio Russo <antonio.e.russo@gmail.com>
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+set -ef
+
+FSLIST="@sysconfdir@/zfs/zfs-list.cache"
+
+[ -d "${FSLIST}" ] || exit 0
+
+do_fail() {
+  printf 'zfs-mount-generator.sh: %s\n' "$*" > /dev/kmsg
+  exit 1
+}
+
+# see systemd.generator
+if [ $# -eq 0 ] ; then
+  dest_norm="/tmp"
+elif [ $# -eq 3 ] ; then
+  dest_norm="${1}"
+else
+  do_fail "zero or three arguments required"
+fi
+
+# For ZFSs marked "auto", a dependency is created for local-fs.target. To
+# avoid regressions, this dependency is reduced to "wants" rather than
+# "requires". **THIS MAY CHANGE**
+req_dir="${dest_norm}/local-fs.target.wants/"
+mkdir -p "${req_dir}"
+
+# All needed information about each ZFS is available from
+# zfs list -H -t filesystem -oname,mountpoint,canmount
+# cached in $FSLIST, and each line is processed by the following function:
+
+process_line() {
+
+  # Check for canmount=off .
+  if [ "${3}" = "off" ] ; then
+    return
+  elif [ "${3}" = "noauto" ] ; then
+    # Don't let a noauto marked mountpoint block an "auto" market mountpoint
+    return
+  elif [ "${3}" = "on" ] ; then
+    : # This is OK
+  else
+    do_fail "invalid canmount"
+  fi
+
+  # Check for legacy and blank mountpoints.
+  if [ "${2}" = "legacy" ] ; then
+    return
+  elif [ "${2}" = "none" ] ; then
+    return
+  elif [ "${2%"${2#?}"}" != "/" ] ; then
+    do_fail "invalid mountpoint $*"
+  fi
+
+  # Escape the mountpoint per systemd policy.
+  mountfile="$(systemd-escape "${2#?}").mount"
+
+  # If the mountpoint has already been created, give it precedence.
+  if [ -e "${dest_norm}/${mountfile}" ] ; then
+    printf 'zfs-mount-generator.sh: %s.mount already exists\n' "${2}" \
+      >/dev/kmsg
+    return
+  fi
+
+  # By ordering before zfs-mount.service, we avoid race conditions.
+  cat > "${dest_norm}/${mountfile}" << EOF
+# Automatically generated by zfs-mount-generator
+
+[Unit]
+SourcePath=${FSLIST}/${cachefile}
+Documentation=man:zfs-mount-generator(8)
+Before=local-fs.target zfs-mount.service
+After=zfs-import.target
+Wants=zfs-import.target
+
+[Mount]
+Where=${2}
+What=${1}
+Type=zfs
+Options=zfsutil,auto
+EOF
+
+  # Finally, create the appropriate dependencies based on the ZFS properties.
+  [ "$3" = "on" ] & ln -s "../${mountfile}" "${req_dir}"
+}
+
+# Feed each line into process_line
+for cachefile in $(ls "${FSLIST}") ; do
+  while read -r fs ; do
+    process_line $fs
+  done < "${FSLIST}/${cachefile}"
+done

man/man8/Makefile.am

@@ -4,6 +4,7 @@ dist_man_MANS = \
 	vdev_id.8 \
 	zdb.8 \
 	zfs.8 \
+	zfs-mount-generator.8 \
 	zfs-program.8 \
 	zgenhostid.8 \
 	zinject.8 \

man/man8/zfs-mount-generator.8

@@ -0,0 +1,56 @@
+.TH "ZFS\-MOUNT\-GENERATOR" "8" "ZFS" "zfs-mount-generator" "\""
+.SH "NAME"
+zfs\-mount\-generator \- generates systemd mount units for zfs
+.SH SYNOPSIS
+.B /lib/systemd/system-generators/zfs\-mount\-generator
+.sp
+.SH DESCRIPTION
+The zfs\-mount\-generator implements the \fBGenerators Specification\fP
+of
+.BR systemd (1),
+and is called during early boot to generate
+.BR systemd.mount (5)
+units for automatically mounted datasets. Mount ordering and dependencies
+are created for all tracked pools (see below). If a dataset has
+.BR canmount=on
+and
+.BR mountpoint
+set, the
+.BR auto
+mount option will be set, and a dependency for
+.BR local-fs.target
+on the mount will be created.
+
+Because zfs pools may not be available very early in the boot process,
+information on ZFS mountpoints must be stored separately. The output
+of the command
+.PP
+.RS 4
+zfs list -H -oname,mountpoint,canmount
+.RE
+.PP
+for datasets that should be mounted by systemd, should be kept
+separate from the pool, at
+.PP
+.RS 4
+.RI @sysconfdir@/zfs/zfs-list.cache/ POOLNAME
+.
+.RE
+.PP
+The cache file, if writeable, will be kept synchronized with the pool
+state by the ZEDLET
+.PP
+.RS 4
+history_event-zfs-list-cacher.sh .
+.RE
+.PP
+.sp
+.SH SEE ALSO
+.BR zfs (5)
+.BR zfs-events (5)
+.BR zed (8)
+.BR zpool (5)
+.BR systemd (1)
+.BR systemd.target (5)
+.BR systemd.special (7)
+.BR systemd.mount (7)

rpm/generic/zfs.spec.in

@@ -338,6 +338,7 @@ systemctl --system daemon-reload >/dev/null || true
 /usr/lib/modules-load.d/*
 %{_unitdir}/*
 %{_presetdir}/*
+%{_generatordir}/*
 %else
 %config(noreplace) %{_sysconfdir}/init.d/*
 %config(noreplace) %{_initconfdir}/zfs