bootctl: rework/modernize "unlink" and add Varlink API for it

Among other things this changes tracking of the location of resources
during GC from using the BootEntrySource enum rather than a path, since
we have that and it is more efficient and easier to grok.

shell-completion/bash/bootctl

@@ -40,8 +40,10 @@ _bootctl() {
                       --dry-run'
         [ARG]='--esp-path --boot-path --root --image --image-policy --install-source
                --variables --random-seed --make-entry-directory --entry-token --json
-               --efi-boot-option-description --secure-boot-auto-enroll --private-key
-               --private-key-source --certificate --certificate-source'
+               --efi-boot-option-description --efi-boot-option-description-with-device
+               --secure-boot-auto-enroll --private-key
+               --private-key-source --certificate --certificate-source
+               --oldest'
     )
 
     if __contains_word "$prev" ${OPTS[ARG]}; then
@@ -67,7 +69,7 @@ _bootctl() {
             --install-source)
                 comps="image host auto"
                 ;;
-            --random-seed|--variables|--secure-boot-auto-enroll)
+            --random-seed|--variables|--secure-boot-auto-enroll|--oldest|--efi-boot-option-description-with-device)
                 comps="yes no"
                 ;;
             --json)
@@ -85,7 +87,7 @@ _bootctl() {
 
     local -A VERBS=(
         [STANDALONE]='help status install update remove is-installed random-seed list set-timeout set-timeout-oneshot cleanup'
-        [BOOTENTRY]='set-default set-oneshot set-sysfail unlink'
+        [BOOTENTRY]='set-default set-oneshot set-sysfail set-preferred unlink'
         [BOOLEAN]='reboot-to-firmware'
         [FILE]='kernel-identify kernel-inspect'
     )

shell-completion/zsh/_bootctl

@@ -24,10 +24,26 @@ _bootctl_set-oneshot() {
     _bootctl_comp_ids
 }
 
+_bootctl_set-sysfail() {
+    _bootctl_comp_ids
+}
+
+_bootctl_set-preferred() {
+    _bootctl_comp_ids
+}
+
 _bootctl_unlink() {
     _bootctl_comp_ids
 }
 
+_bootctl_kernel-identify() {
+    _files
+}
+
+_bootctl_kernel-inspect() {
+    _files
+}
+
 _bootctl_reboot-to-firmware() {
     local -a _completions
     _completions=( yes no )
@@ -49,10 +65,14 @@ _bootctl_reboot-to-firmware() {
         "list:List boot loader entries"
         "set-default:Set the default boot loader entry"
         "set-oneshot:Set the default boot loader entry only for the next boot"
+        "set-sysfail:Set boot loader entry used in case of a system failure"
+        "set-preferred:Set the preferred boot loader entry"
         "set-timeout:Set the menu timeout"
         "set-timeout-oneshot:Set the menu timeout for the next boot only"
         "unlink:Remove boot loader entry"
         "cleanup:Remove files in ESP not referenced in any boot entry"
+        "kernel-identify:Identify kernel image type"
+        "kernel-inspect:Print details about the kernel image"
     )
     if (( CURRENT == 1 )); then
         _describe -t commands 'bootctl command' _bootctl_cmds || compadd "$@"
@@ -79,6 +99,7 @@ _arguments \
     '--no-pager[Do not pipe output into a pager]' \
     '--graceful[Do not fail when locating ESP or writing fails]' \
     '--dry-run[Dry run (unlink and cleanup)]' \
+    '--oldest=[Delete oldest boot menu entry]:options:(yes no)' \
     '--root=[Operate under the specified directory]:PATH' \
     '--image=[Operate on the specified image]:PATH' \
     '--install-source[Where to pick files when using --root=/--image=]:options:(image host auto)' \