From 61e20312ff66ab8d9af6ed2963ffc3acca50b14e Mon Sep 17 00:00:00 2001
From: pennae <pennae.git@eno.space>
Date: Thu, 28 Sep 2023 02:14:29 +0200
Subject: add reload-only deployment option

this is mostly useful for things like static dhcp lease tables. reboots
may be a bit harsh for those.
---
 openwrt/config_generation.sh | 50 ++++++++++++++++++++++++++++++++------
 openwrt/default.nix          | 58 ++++++++++++++++++++++++++++++++++++++------
 2 files changed, 93 insertions(+), 15 deletions(-)

diff --git a/openwrt/config_generation.sh b/openwrt/config_generation.sh
index 8c3dde0..f4b25c5 100644
--- a/openwrt/config_generation.sh
+++ b/openwrt/config_generation.sh
@@ -1,6 +1,6 @@
 #!/bin/sh /etc/rc.common
 
-EXTRA_COMMANDS="apply commit"
+EXTRA_COMMANDS="apply_reboot prepare_reload apply_reload commit"
 START=99
 
 _unregister_script() {
@@ -21,7 +21,7 @@ _rollback() {
     fi
 }
 
-apply() {
+_prepare_apply() {
     CYAN='\e[36m'
     RED='\e[31m'
     NORMAL='\e[0m'
@@ -55,18 +55,24 @@ apply() {
         rm -rf /overlay/upper.prev
         exit 1
     fi
+}
+
+_run_steps() {
+    (
+        set -e
+        @deploy_steps@
+    )
+}
+
+apply_reboot() {
+    _prepare_apply
 
     # everything after this point may fail. if it does we'll simply roll back
     # immediately and reboot.
 
     trap 'reboot &' EXIT
 
-    if ! (
-        set -e
-
-        @deploy_steps@
-    )
-    then
+    if ! _run_steps; then
         log_err 'deployment failed, rolling back and rebooting ...'
         _rollback
         exit 1
@@ -75,6 +81,34 @@ apply() {
     log 'rebooting device ...'
 }
 
+prepare_reload() {
+    mkdir /overlay/upper.prev
+    /etc/init.d/config_generation enable
+}
+
+apply_reload() {
+    _prepare_apply
+
+    # everything after this point may fail. if it does we'll simply roll back
+    # immediately and reboot.
+
+    trap 'reboot &' EXIT
+
+    if _run_steps; then
+        trap '' EXIT
+        log 'reloading config ...'
+        reload_config
+        # give service restarts a chance
+        log 'waiting @reload_service_wait@s for services ...'
+        sleep @reload_service_wait@
+        exit 0
+    else
+        log_err 'deployment failed, rolling back and rebooting ...'
+        _rollback
+        exit 1
+    fi
+}
+
 commit() {
     if ! [ -e /overlay/upper.prev ]; then
         exit 1
diff --git a/openwrt/default.nix b/openwrt/default.nix
index 47f2946..c9ae707 100644
--- a/openwrt/default.nix
+++ b/openwrt/default.nix
@@ -52,6 +52,23 @@ let
               ::: {.warning}
               Values under `20` will very likely cause spurious rollbacks.
               :::
+
+              ::: {.notice}
+              During reload-only deployment this timeout *includes* the time needed to apply
+              configuration, which may be substatial if network activity is necessary (eg when
+              installing packages).
+              :::
+            '';
+          };
+
+          reloadServiceWait = lib.mkOption {
+            type = lib.types.ints.unsigned;
+            default = 10;
+            description = ''
+              How long to wait (in seconds) during reload-only deployment to allow for more
+              graceful service restarts. Small values make reloads faster, but since OpenWRT
+              has no mechanism to figure out *when* all services are done starting this also
+              introduces possible failure points.
             '';
           };
         };
@@ -102,13 +119,16 @@ let
                     steps}
                 '';
                 rollback_timeout = config.deploy.rollbackTimeout;
+                reload_service_wait = config.deploy.reloadServiceWait;
             } ''
               substitute "$src" "$out" \
                 --subst-var deploy_steps \
-                --subst-var rollback_timeout
+                --subst-var rollback_timeout \
+                --subst-var reload_service_wait
               chmod +x "$out"
             '';
-            timeout = config.deploy.rollbackTimeout + config.deploy.rebootAllowance;
+            rebootTimeout = config.deploy.rollbackTimeout + config.deploy.rebootAllowance;
+            reloadTimeout = config.deploy.rollbackTimeout + config.deploy.reloadServiceWait;
             sshOpts =
               ''-o ControlPath="$TMP/cm" ''
               + lib.escapeShellArgs
@@ -147,7 +167,7 @@ let
               TAG="apply_config_$$_$RANDOM"
 
               ssh() {
-                command ssh ${sshOpts} device "$@"
+                command ssh -n ${sshOpts} device "$@"
               }
 
               scp() {
@@ -155,6 +175,16 @@ let
               }
 
               main() {
+                RELOAD_ONLY=false
+                TIMEOUT=${toString rebootTimeout}s
+
+                case "$@" in
+                  --reload) RELOAD_ONLY=true
+                            TIMEOUT=${toString reloadTimeout}s
+                            ;;
+                  "") ;;
+                esac
+
                 export TMP="$(umask 0077; mktemp -d)"
 
                 trap '
@@ -172,11 +202,25 @@ let
                 # apply the new config and wait for the box to go down via ssh connection
                 # timeout.
                 log 'applying config'
-                ssh '/etc/init.d/config_generation apply </dev/null 2>&1 | logger -t '"$TAG" &
-                ssh 'logread -l9999 -f' | awk -v FS="$TAG: " '$2 { print $2 }' || true
+                if $RELOAD_ONLY; then
+                  ssh 'logread -l9999 -f' &
+                  ssh '/etc/init.d/config_generation prepare_reload'
+                  ssh '/etc/init.d/config_generation start' &
+                  ssh '/etc/init.d/config_generation apply_reload 2>&1 | logger -t '"$TAG"
+                  ssh -O exit
+                else
+                  ssh 'logread -l9999 -f' &
+                  ssh 'service config_generation apply_reboot 2>&1 | logger -t '"$TAG"
+                  # if the previous command succeeded we're up for a reboot, at which
+                  # point ssh will exit with a 255 status
+                  wait %1 || true
+                fi \
+                  | awk -v FS="$TAG: " '
+                      $2 { print $2 }
+                    '
 
                 log 'waiting for device to return'
-                __DO_WAIT=1 timeout --foreground ${toString timeout}s "$0" || {
+                __DO_WAIT=1 timeout --foreground $TIMEOUT "$0" || {
                   log_err 'configuration change failed, device will roll back and reboot'
                   exit 1
                 }
@@ -191,7 +235,7 @@ let
               }
 
               case "''${__DO_WAIT:-}" in
-                "") main ;;
+                "") main "$@" ;;
                 *) _wait ;;
               esac
             '';
-- 
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