systemd zvol target

Modify the recent zfs-volumes.target to Requires= zfs-volume@.service
units that are dynamically generated for each zvol by the existing
systemd-generator infrastructure at boot time.  This is an alternative
to the zfs-volume-wait.service.

Each unit polls once per second, exiting if it detects the zvol link,
succeeding unconditionally after a 30 second timeout.

Signed-off-by: Antonio Russo <antonio.e.russo@gmail.com>

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

@@ -65,6 +65,11 @@ PROPS="name,mountpoint,canmount,atime,relatime,devices,exec,readonly"
 PROPS="${PROPS},setuid,nbmand,encroot,keylocation"
 
 "${ZFS}" list -H -t filesystem -o $PROPS -r "${ZEVENT_POOL}" > "${FSLIST_TMP}"
+"${ZFS}" list -H -t volume -o name -r "${ZEVENT_POOL}" | while read -r name
+do
+    # fake "zvol" mountpoint
+    printf '%s\tzvol\toff\n' "$name" >> "${FSLIST_TMP}"
+done
 
 # Sort the output so that it is stable
 sort "${FSLIST_TMP}" -o "${FSLIST_TMP}"

etc/systemd/system-generators/Makefile.am

@@ -9,6 +9,7 @@ $(systemdgenerator_SCRIPTS): %: %.in
 		-e 's,@runstatedir\@,$(runstatedir),g' \
 		-e 's,@sbindir\@,$(sbindir),g' \
 		-e 's,@sysconfdir\@,$(sysconfdir),g' \
+		-e 's,@systemdunitdir\@,$(systemdunitdir),g' \
 		$< >'$@'
 
 # Double-colon rules are allowed; there are multiple independent definitions.

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

@@ -46,6 +46,8 @@ fi
 # avoid regressions, this dependency is reduced to "wants" rather than
 # "requires". **THIS MAY CHANGE**
 req_dir="${dest_norm}/local-fs.target.wants/"
+zvol_reqdir="${dest_norm}/zfs-volumes.target.requires"
+mkdir -p "${zvol_reqdir}"
 mkdir -p "${req_dir}"
 
 # All needed information about each ZFS is available from
@@ -74,6 +76,14 @@ process_line() {
   p_encroot="${11}"
   p_keyloc="${12}"
 
+  if [ "${p_mountpoint}" = "zvol" ] ; then
+    # special case of zvol
+    unit="zfs-volume@$(systemd-escape "${dataset}").service"
+    ln -s "@systemdunitdir@/zfs-volume@.service" \
+        "${zvol_reqdir}/${unit}"
+    return
+  fi
+
   # Check for canmount=off .
   if [ "${p_canmount}" = "off" ] ; then
     return

etc/systemd/system/50-zfs.preset.in

@@ -4,6 +4,8 @@ disable zfs-import-scan.service
 enable zfs-import.target
 enable zfs-mount.service
 enable zfs-share.service
+disable zfs-volumes.target
+disable zfs-volume@.service
 enable zfs-zed.service
 enable zfs-volume-wait.service
 enable zfs.target

etc/systemd/system/Makefile.am

@@ -9,6 +9,7 @@ systemdunit_DATA = \
 	zfs-share.service \
 	zfs-volume-wait.service \
 	zfs-import.target \
+	zfs-volume@.service \
 	zfs-volumes.target \
 	zfs.target
 
@@ -18,6 +19,7 @@ EXTRA_DIST = \
 	$(top_srcdir)/etc/systemd/system/zfs-import-scan.service.in \
 	$(top_srcdir)/etc/systemd/system/zfs-mount.service.in \
 	$(top_srcdir)/etc/systemd/system/zfs-share.service.in \
+	$(top_srcdir)/etc/systemd/system/zfs-volume@.service.in \
 	$(top_srcdir)/etc/systemd/system/zfs-import.target.in \
 	$(top_srcdir)/etc/systemd/system/zfs-volume-wait.service.in \
 	$(top_srcdir)/etc/systemd/system/zfs-volumes.target.in \

etc/systemd/system/zfs-volume@.service.in

@@ -0,0 +1,9 @@
+[Unit]
+Description=ZFS zvol %I ready
+Before=zfs-volumes.target
+DefaultDependencies=no
+
+[Service]
+ExecStart=/bin/sh -c 'timeout=30 ; while [ $timeout -gt 0 ] ; do [ -e "/dev/zvol/$0" ] && exit 0 ; sleep 1 ; timeout=$((timeout-1)); done ; echo "zvol $0 unavailable"' %I
+Type=oneshot
+RemainAfterExit=yes