zkexec: recovery shell arbitrary kexec wrapper

zkexec is designed to allow a user to easily kexec any kernel and
initramfs found in a boot environment. It will tab complete any file in
/boot in the ZFS file system provided as the first argument. No
validation is performed - it willy happily load a kernel as an initramfs
and vice-versa.

Closes #201

90zfsbootmenu/help-files/134/recovery-shell.pod

@@ -7,9 +7,13 @@
 zfsbootmenu
   Launch the interactive boot environment menu.
 
-zfs-chroot zfs filesystem
+zfs-chroot filesystem
   Enter a chroot of the specified boot environment. The boot environment is mounted read/write if the zpool is imported read/write.
 
+zkexec filesystem kernel initramfs
+  Directly kexec a kernel and initramfs from a boot environment, allowing any kernel and initramfs to be loaded into memory and
+  immediately booted.
+
 set_rw_pool pool
   Export, then re-import the pool read/write.
 

90zfsbootmenu/help-files/54/recovery-shell.pod

@@ -7,11 +7,16 @@
 zfsbootmenu
   Launch the interactive boot environment menu.
 
-zfs-chroot zfs filesystem
+zfs-chroot filesystem
   Enter a chroot of the specified boot environment.
   The boot environment is mounted read/write if the
   zpool is imported read/write.
 
+zkexec filesystem kernel initramfs
+  Directly kexec a kernel and initramfs from a boot
+  environment, allowing any kernel and initramfs to be
+  loaded into memory and immediately booted.
+
 set_rw_pool pool
   Export, then re-import the pool read/write.
 

90zfsbootmenu/help-files/94/recovery-shell.pod

@@ -7,10 +7,14 @@
 zfsbootmenu
   Launch the interactive boot environment menu.
 
-zfs-chroot zfs filesystem
+zfs-chroot filesystem
   Enter a chroot of the specified boot environment. The boot environment is mounted read/write
   if the zpool is imported read/write.
 
+zkexec filesystem kernel initramfs
+  Directly kexec a kernel and initramfs from a boot environment, allowing any kernel and
+  initramfs to be loaded into memory and immediately booted.
+
 set_rw_pool pool
   Export, then re-import the pool read/write.
 

90zfsbootmenu/module-setup.sh

@@ -156,6 +156,7 @@ install() {
   inst_simple "${moddir}/zfsbootmenu.sh" "/bin/zfsbootmenu" || _ret=$?
   inst_simple "${moddir}/zlogtail.sh" "/bin/zlogtail" || _ret=$?
   inst_simple "${moddir}/ztrace.sh" "/bin/ztrace" || _ret=$?
+  inst_simple "${moddir}/zkexec.sh" "/bin/zkexec" || _ret=$?
   inst_hook cmdline 95 "${moddir}/zfsbootmenu-parse-commandline.sh" || _ret=$?
   inst_hook pre-mount 90 "${moddir}/zfsbootmenu-preinit.sh" || _ret=$?
 

90zfsbootmenu/zfsbootmenu-completions.sh

@@ -70,3 +70,34 @@ _mount_zfs() {
   COMPREPLY=( $( compgen -W "${ZFS[*]}" -- "${COMP_WORDS[1]}" ) )
 }
 complete -F _mount_zfs mount_zfs
+
+_zkexec() {
+  local ARG index
+  COMPREPLY=()
+
+  shopt -s nullglob
+
+  index="${#COMP_WORDS[@]}"
+  case "${index}" in
+    2)
+      for FS in $( zfs list -H -o name ) ; do
+        ARG+=("${FS}")
+      done
+
+      COMPREPLY=( $( compgen -W "${ARG[*]}" -- "${COMP_WORDS[1]}" ) )
+    ;;
+    3|4)
+      mp="$( mount_zfs "${COMP_WORDS[1]}" )"
+      [ -d "${mp}/boot" ] || return
+
+      for BIN in "${mp}"/boot/* ; do
+        BIN="${BIN##*/}"
+        ARG+=("${BIN}")
+      done
+      umount "${mp}"
+      COMPREPLY=( $( compgen -W "${ARG[*]}" -- "${COMP_WORDS[$(( index - 1))]}" ) )
+    ;;
+  esac
+
+}
+complete -F _zkexec zkexec

90zfsbootmenu/zkexec.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+# shellcheck disable=SC1091
+[ -f /lib/zfsbootmenu-lib.sh ] && source /lib/zfsbootmenu-lib.sh
+
+if [ $# -ne 3 ] ; then
+ echo "Usage: $0 filesystem kernel initramfs"
+ exit
+fi
+
+fs="${1}"
+kernel="/boot/${2}"
+initramfs="/boot/${3}"
+
+kexec_kernel "${fs} ${kernel} ${initramfs}"

pod/online/recovery-shell.pod

@@ -12,10 +12,14 @@ B<zfsbootmenu> - Recovery Shell
 
 Launch the interactive boot environment menu.
 
-=item I<zfs-chroot> B<zfs filesystem>
+=item I<zfs-chroot> B<filesystem>
 
 Enter a chroot of the specified boot environment. The boot environment is mounted I<read/write> if the zpool is imported I<read/write>.
 
+=item I<zkexec> B<filesystem> B<kernel> B<initramfs>
+
+Directly I<kexec> a kernel and initramfs from a boot environment, allowing any kernel and initramfs to be loaded into memory and immediately booted.
+
 =item I<set_rw_pool> B<pool>
 
 Export, then re-import the pool I<read/write>.