zfsbootmenu: extend zbm.prefer to set bootfs

Author: zdykstra

docs/man/zfsbootmenu.7.rst

@@ -20,17 +20,18 @@ These options are set on the kernel command line when booting the initramfs or U
 
 **zbm.prefer**
 
-  ZFSBootMenu will attempt to import as many pools as possible to identify boot environments and will, by default, look for the *bootfs* property on the first imported pool (sorted alphabetically) to select the default boot environment. This option controls this behavior.
+  ZFSBootMenu attempts to import all detected pools by default, with the *bootfs* property on the first pool (sorted alphabetically) used to select the default boot environment. Providing a *pool* name for this parameter will override the pool import order. Providing a *dataset* for this parameter will override both the pool import order and the default boot environment.
 
-  **zbm.prefer=<pool>**
 
-    The simplest form attempts to import **<pool>** before any other pool. The *bootfs* value from this pool will control the default boot environment.
+  **zbm.prefer=<pool|dataset>**
 
-  **zbm.prefer=<pool>!**
+    The simplest form attempts to import **<pool>** or the pool component of a **<dataset>** before any other pool. If a *dataset* is provided, that will be used as the boot environment if it exists.
+
+  **zbm.prefer=<pool|dataset>!**
 
     If a literal *!* has been appended to the pool name, ZFSBootMenu will insist on successfully importing the named pool before attempting to import any others.
 
-  **zbm.prefer=<pool>!!**
+  **zbm.prefer=<pool|dataset>!!**
 
     If a literal *!!* has been appended to the pool name, ZFSBootMenu will insist on successfully importing the named pool and no others.
 

zfsbootmenu/init.d/50-import-pools

@@ -105,17 +105,25 @@ if [ "${unsupported}" -ne 0 ]; then
 fi
 unset unsupported
 
-# Attempt to find the bootfs property
-# shellcheck disable=SC2086
-while read -r _bootfs; do
-  if [ "${_bootfs}" = "-" ]; then
-    BOOTFS=
+if [ -n "${zbm_prefer_bootfs}" ]; then
+  if is_zfs_filesystem "${zbm_prefer_bootfs}" ; then
+    BOOTFS="${zbm_prefer_bootfs}"
   else
-    BOOTFS="${_bootfs}"
-    break
+    zerror "bootfs value '${zbm_prefer_bootfs}' not a ZFS dataset"
   fi
-done <<<"$( zpool list -H -o bootfs "${zbm_prefer_pool:---}" )"
-unset _bootfs
+else
+  # Attempt to find the bootfs property
+  # shellcheck disable=SC2086
+  while read -r _bootfs; do
+    if [ "${_bootfs}" = "-" ]; then
+      BOOTFS=
+    else
+      BOOTFS="${_bootfs}"
+      break
+    fi
+  done <<<"$( zpool list -H -o bootfs "${zbm_prefer_pool:---}" )"
+  unset _bootfs
+fi
 
 if [ -n "${BOOTFS}" ]; then
   export BOOTFS

zfsbootmenu/pre-init/zfsbootmenu-parse-commandline.sh

@@ -219,35 +219,41 @@ if kcl_override=$( get_zbm_arg zbm.kcl_override ) ; then
   zinfo "overriding all BE KCLs with: '$( kcl_assemble < "${BASE}/cmdline" )'"
 fi
 
-zbm_prefer_pool=
-if zbm_prefer_pool=$( get_zbm_arg zbm.prefer ) ; then
-  # shellcheck disable=SC2034
-  zbm_prefer_pool="${zbm_prefer_pool%%/*}"
-  zinfo "preferring ${zbm_prefer_pool} for bootfs"
-fi
-
 zbm_wait_for_devices=
 if zbm_wait_for_devices=$( get_zbm_arg zbm.wait_for ) ; then
   zinfo "system will wait for ${zbm_wait_for_devices}"
 fi
 
-# pool! : this pool must be imported before all others
-# pool!!: this pool, and no others, must be imported
+zbm_prefer_bootfs=
+zbm_require_pool=
+if zbm_prefer=$( get_zbm_arg zbm.prefer ) ; then
 
-# shellcheck disable=SC2034
-case "${zbm_prefer_pool}" in
-  *!!)
-    zbm_require_pool="only"
-    zbm_prefer_pool="${zbm_prefer_pool%!!}"
-    ;;
-  *!)
-    zbm_require_pool="yes"
-    zbm_prefer_pool="${zbm_prefer_pool%!}"
-    ;;
-  *)
-    zbm_require_pool=""
-    ;;
-esac
+  # strip the modifiers and set zbm_require_pool as needed
+  # shellcheck disable=SC2034
+  case "${zbm_prefer}" in
+    *!!)
+      zbm_require_pool="only"
+      zbm_prefer="${zbm_prefer%!!}"
+      zinfo "will only attempt to import ${zbm_prefer%%/*}"
+      ;;
+    *!)
+      zbm_require_pool="yes"
+      zbm_prefer="${zbm_prefer%!}"
+      zinfo "requiring pool ${zbm_prefer%%/*}"
+      ;;
+    *)
+      zbm_require_pool=
+      ;;
+  esac
+
+  zbm_prefer_pool="${zbm_prefer%%/*}"
+
+  # zbm_prefer looks like it could be a dataset, use it as the bootfs value
+  if [ "${zbm_prefer_pool}" != "${zbm_prefer}" ]; then
+    # shellcheck disable=SC2034
+    zbm_prefer_bootfs="${zbm_prefer}"
+  fi
+fi
 
 # Make sure Dracut is happy that we have a root
 

zfsbootmenu/pre-init/zfsbootmenu-preinit.sh

@@ -28,6 +28,7 @@ export menu_timeout='${menu_timeout}'
 export loglevel='${loglevel}'
 export zbm_prefer_pool='${zbm_prefer_pool}'
 export zbm_require_pool='${zbm_require_pool}'
+export zbm_prefer_bootfs='${zbm_prefer_bootfs}'
 export default_hostid=00bab10c
 export zbm_sort='${zbm_sort}'
 export zbm_set_hostid='${zbm_set_hostid}'