Systemd mount generator: Generate noauto units; add control properties

This commit refactors the systemd mount generators and makes the
following major changes:

- The generator now generates units for datasets marked canmount=noauto,
  too. These units are NOT WantedBy local-fs.target.
  If there are multiple noauto datasets for a path, no noauto unit will
  be created. Datasets with canmount=on are prioritized.

- Introduces handling of new user properties which are now included in
  the zfs-list.cache files:
    - org.openzfs.systemd:requires:
      List of units to require for this mount unit
    - org.openzfs.systemd:requires-mounts-for:
      List of mounts to require by this mount unit
    - org.openzfs.systemd:before:
      List of units to order after this mount unit
    - org.openzfs.systemd:after:
      List of units to order before this mount unit
    - org.openzfs.systemd:wanted-by:
      List of units to add a Wants dependency on this mount unit to
    - org.openzfs.systemd:required-by:
      List of units to add a Requires dependency on this mount unit to
    - org.openzfs.systemd:nofail:
      Toggles between a wants and a requires dependency.
    - org.openzfs.systemd:ignore:
      Do not generate a mount unit for this dataset.

  Consult the updated man page for detailed documentation.

- Restructures and extends the zfs-mount-generator(8) man page with the
  above properties, information on unit ordering and a license header.

Reviewed-by: Richard Laager <[email protected]>
Reviewed-by: Antonio Russo <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: InsanePrawn <[email protected]>
Closes #9649

1 files changed, 191 insertions, 26 deletions

diff --git a/etc/systemd/system-generators/zfs-mount-generator.in b/etc/systemd/system-generators/zfs-mount-generator.in
index 411b3f955..bb735112d 100755
--- a/etc/systemd/system-generators/zfs-mount-generator.in
+++ b/etc/systemd/system-generators/zfs-mount-generator.in
@@ -2,6 +2,7 @@
 
 # zfs-mount-generator - generates systemd mount units for zfs
 # Copyright (c) 2017 Antonio Russo <[email protected]>
+# Copyright (c) 2020 InsanePrawn <[email protected]>
 #
 # Permission is hereby granted, free of charge, to any person obtaining
 # a copy of this software and associated documentation files (the
@@ -33,6 +34,35 @@ do_fail() {
   exit 1
 }
 
+# test if $1 is in space-separated list $2
+is_known() {
+  query="$1"
+  IFS=' '
+  # protect against special characters
+  set -f
+  for element in $2 ; do
+    if [ "$query" = "$element" ] ; then
+      return 0
+    fi
+  done
+  return 1
+}
+
+# create dependency on unit file $1
+# of type $2, i.e. "wants" or "requires"
+# in the target units from space-separated list $3
+create_dependencies() {
+  unitfile="$1"
+  suffix="$2"
+  # protect against special characters
+  set -f
+  for target in $3 ; do
+    target_dir="${dest_norm}/${target}.${suffix}/"
+    mkdir -p "${target_dir}"
+    ln -s "../${unitfile}" "${target_dir}"
+  done
+}
+
 # see systemd.generator
 if [ $# -eq 0 ] ; then
   dest_norm="/tmp"
@@ -42,11 +72,6 @@ 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 -o <properties>
@@ -74,18 +99,58 @@ process_line() {
   p_nbmand="${10}"
   p_encroot="${11}"
   p_keyloc="${12}"
+  p_systemd_requires="${13}"
+  p_systemd_requiresmountsfor="${14}"
+  p_systemd_before="${15}"
+  p_systemd_after="${16}"
+  p_systemd_wantedby="${17}"
+  p_systemd_requiredby="${18}"
+  p_systemd_nofail="${19}"
+  p_systemd_ignore="${20}"
 
   # Minimal pre-requisites to mount a ZFS dataset
+  # By ordering before zfs-mount.service, we avoid race conditions.
+  after="zfs-import.target"
+  before="zfs-mount.service"
   wants="zfs-import.target"
+  requires=""
+  requiredmounts=""
+  wantedby=""
+  requiredby=""
+  noauto="off"
+
+  if [ -n "${p_systemd_after}" ] && \
+      [ "${p_systemd_after}" != "-" ] ; then
+    after="${p_systemd_after} ${after}"
+  fi
+
+  if [ -n "${p_systemd_before}" ] && \
+      [ "${p_systemd_before}" != "-" ] ; then
+    before="${p_systemd_before} ${before}"
+  fi
+
+  if [ -n "${p_systemd_requires}" ] && \
+      [ "${p_systemd_requires}" != "-" ] ; then
+    requires="Requires=${p_systemd_requires}"
+  fi
+
+  if [ -n "${p_systemd_requiresmountsfor}" ] && \
+      [ "${p_systemd_requiresmountsfor}" != "-" ] ; then
+    requiredmounts="RequiresMountsFor=${p_systemd_requiresmountsfor}"
+  fi
 
   # Handle encryption
   if [ -n "${p_encroot}" ] &&
       [ "${p_encroot}" != "-" ] ; then
     keyloadunit="zfs-load-key-$(systemd-escape "${p_encroot}").service"
     if [ "${p_encroot}" = "${dataset}" ] ; then
-        pathdep=""
+      keymountdep=""
       if [ "${p_keyloc%%://*}" = "file" ] ; then
-        pathdep="RequiresMountsFor='${p_keyloc#file://}'"
+        if [ -n "${requiredmounts}" ] ; then
+          keymountdep="${requiredmounts} '${p_keyloc#file://}'"
+        else
+          keymountdep="RequiresMountsFor='${p_keyloc#file://}'"
+        fi
         keyloadcmd="@sbindir@/zfs load-key '${dataset}'"
       elif [ "${p_keyloc}" = "prompt" ] ; then
         keyloadcmd="\
@@ -121,8 +186,10 @@ SourcePath=${cachefile}
 Documentation=man:zfs-mount-generator(8)
 DefaultDependencies=no
 Wants=${wants}
-After=${wants}
-${pathdep}
+After=${after}
+Before=${before}
+${requires}
+${keymountdep}
 
 [Service]
 Type=oneshot
@@ -130,23 +197,35 @@ RemainAfterExit=yes
 ExecStart=${keyloadcmd}
 ExecStop=@sbindir@/zfs unload-key '${dataset}'"   > "${dest_norm}/${keyloadunit}"
     fi
-    # Update the dependencies for the mount file to require the
+    # Update the dependencies for the mount file to want the
     # key-loading unit.
     wants="${wants} ${keyloadunit}"
+    after="${after} ${keyloadunit}"
   fi
 
   # Prepare the .mount unit
 
+  # skip generation of the mount unit if org.openzfs.systemd:ignore is "on"
+  if [ -n "${p_systemd_ignore}" ] ; then
+    if [ "${p_systemd_ignore}" = "on" ] ; then
+      return
+    elif [ "${p_systemd_ignore}" = "-" ] \
+      || [ "${p_systemd_ignore}" = "off" ] ; then
+      : # This is OK
+    else
+      do_fail "invalid org.openzfs.systemd:ignore for ${dataset}"
+    fi
+  fi
+
   # Check for canmount=off .
   if [ "${p_canmount}" = "off" ] ; then
     return
   elif [ "${p_canmount}" = "noauto" ] ; then
-    # Don't let a noauto marked mountpoint block an "auto" marked mountpoint
-    return
+    noauto="on"
   elif [ "${p_canmount}" = "on" ] ; then
     : # This is OK
   else
-    do_fail "invalid canmount"
+    do_fail "invalid canmount for ${dataset}"
   fi
 
   # Check for legacy and blank mountpoints.
@@ -155,7 +234,7 @@ ExecStop=@sbindir@/zfs unload-key '${dataset}'"   > "${dest_norm}/${keyloadunit}
   elif [ "${p_mountpoint}" = "none" ] ; then
     return
   elif [ "${p_mountpoint%"${p_mountpoint#?}"}" != "/" ] ; then
-    do_fail "invalid mountpoint $*"
+    do_fail "invalid mountpoint for ${dataset}"
   fi
 
   # Escape the mountpoint per systemd policy.
@@ -233,15 +312,91 @@ ExecStop=@sbindir@/zfs unload-key '${dataset}'"   > "${dest_norm}/${keyloadunit}
       "${dataset}" >/dev/kmsg
   fi
 
-  # If the mountpoint has already been created, give it precedence.
+  if [ -n "${p_systemd_wantedby}" ] && \
+      [ "${p_systemd_wantedby}" != "-" ] ; then
+    noauto="on"
+    if [ "${p_systemd_wantedby}" = "none" ] ; then
+      wantedby=""
+    else
+      wantedby="${p_systemd_wantedby}"
+      before="${before} ${wantedby}"
+    fi
+  fi
+
+  if [ -n "${p_systemd_requiredby}" ] && \
+      [ "${p_systemd_requiredby}" != "-" ] ; then
+    noauto="on"
+    if [ "${p_systemd_requiredby}" = "none" ] ; then
+      requiredby=""
+    else
+      requiredby="${p_systemd_requiredby}"
+      before="${before} ${requiredby}"
+    fi
+  fi
+
+  # For datasets with canmount=on, a dependency is created for
+  # local-fs.target by default. To avoid regressions, this dependency
+  # is reduced to "wants" rather than "requires" when nofail is not "off".
+  # **THIS MAY CHANGE**
+  # noauto=on disables this behavior completely.
+  if [ "${noauto}" != "on" ] ; then
+    if [ "${p_systemd_nofail}" = "off" ] ; then
+      requiredby="local-fs.target"
+      before="${before} local-fs.target"
+    else
+      wantedby="local-fs.target"
+      if [ "${p_systemd_nofail}" != "on" ] ; then
+        before="${before} local-fs.target"
+      fi
+    fi
+  fi
+
+  # Handle existing files:
+  # 1.  We never overwrite existing files, although we may delete
+  #     files if we're sure they were created by us. (see 5.)
+  # 2.  We handle files differently based on canmount. Units with canmount=on
+  #     always have precedence over noauto. This is enforced by the sort pipe
+  #     in the loop around this function.
+  #     It is important to use $p_canmount and not $noauto here, since we
+  #     sort by canmount while other properties also modify $noauto, e.g.
+  #     org.openzfs.systemd:wanted-by.
+  # 3.  If no unit file exists for a noauto dataset, we create one.
+  #     Additionally, we use $noauto_files to track the unit file names
+  #     (which are the systemd-escaped mountpoints) of all (exclusively)
+  #     noauto datasets that had a file created.
+  # 4.  If the file to be created is found in the tracking variable,
+  #     we do NOT create it.
+  # 5.  If a file exists for a noauto dataset, we check whether the file
+  #     name is in the variable. If it is, we have multiple noauto datasets
+  #     for the same mountpoint. In such cases, we remove the file for safety.
+  #     To avoid further noauto datasets creating a file for this path again,
+  #     we leave the file name in the tracking variable.
   if [ -e "${dest_norm}/${mountfile}" ] ; then
-    printf 'zfs-mount-generator: %s already exists\n' "${mountfile}" \
-      >/dev/kmsg
+    if is_known "$mountfile" "$noauto_files" ; then
+      # if it's in $noauto_files, we must be noauto too. See 2.
+      printf 'zfs-mount-generator: removing duplicate noauto %s\n' \
+        "${mountfile}" >/dev/kmsg
+      # See 5.
+      rm "${dest_norm}/${mountfile}"
+    else
+      # don't log for canmount=noauto
+      if [  "${p_canmount}" = "on" ] ; then
+        printf 'zfs-mount-generator: %s already exists. Skipping.\n' \
+          "${mountfile}" >/dev/kmsg
+      fi
+    fi
+    # file exists; Skip current dataset.
     return
+  else
+    if is_known "${mountfile}" "${noauto_files}" ; then
+      # See 4.
+      return
+    elif [ "${p_canmount}" = "noauto" ] ; then
+      noauto_files="${mountfile} ${noauto_files}"
+    fi
   fi
 
   # Create the .mount unit file.
-  # By ordering before zfs-mount.service, we avoid race conditions.
   #
   # (Do not use `<<EOF`-style here-documents for this, see warning above)
   #
@@ -251,9 +406,12 @@ ExecStop=@sbindir@/zfs unload-key '${dataset}'"   > "${dest_norm}/${keyloadunit}
 [Unit]
 SourcePath=${cachefile}
 Documentation=man:zfs-mount-generator(8)
-Before=local-fs.target zfs-mount.service
-After=${wants}
+
+Before=${before}
+After=${after}
 Wants=${wants}
+${requires}
+${requiredmounts}
 
 [Mount]
 Where=${p_mountpoint}
@@ -261,13 +419,20 @@ What=${dataset}
 Type=zfs
 Options=defaults${opts},zfsutil" > "${dest_norm}/${mountfile}"
 
-  # Finally, create the appropriate dependency
-  ln -s "../${mountfile}" "${req_dir}"
+  # Finally, create the appropriate dependencies
+  create_dependencies "${mountfile}" "wants" "$wantedby"
+  create_dependencies "${mountfile}" "requires" "$requiredby"
+
 }
 
-# Feed each line into process_line
 for cachefile in "${FSLIST}/"* ; do
-  while read -r fs ; do
-    process_line "${fs}"
-  done < "${cachefile}"
+  # Sort cachefile's lines by canmount, "on" before "noauto"
+  # and feed each line into process_line
+  sort -t "$(printf '\t')" -k 3 -r "${cachefile}" | \
+  ( # subshell is necessary for `sort|while read` and $noauto_files
+    noauto_files=""
+    while read -r fs ; do
+      process_line "${fs}"
+    done
+  )
 done