Subject: [bug#33508] [PATCH] gnu: Add ability to restart services on system reconfigure

From: Carlo Zancanaro <[email-masked]>
Date: Sat, 01 Dec 2018 13:31:48 +1100

Hey Clément,

I'm still working through my thoughts on how all of this should 
work. I feel like there are a few different use-cases that change 
the trade-offs (eg. servers vs desktops, multi-user vs 
single-user) and I don't know what the best defaults are, or the 
most useful ways to vary that behaviour.

I've attached my most recent version of my patches. I haven't had 
a chance to test them (so they may have really dumb mistakes), but 
they should implement the idea of restart-actions as procedures.

On Fri, Nov 30 2018, Clément Lassieur wrote:
> It could also detect whether you pass a symbol or a procedure. 
> In most cases that would be a symbol which would allow static 
> analysis.  But one could still customize it with a procedure.

I don't like this way of having two different representations for 
the same thing. In my current implementation there are three 
procedures, {always,manually,never}-restart, which can be used 
directly in the place of the old symbols (thus we can check for 
those strategies with eq?).

Carlo

>From 25d631b33b84f1f48bc06a192c46eb3170e29b97 Mon Sep 17 00:00:00 2001
From: Carlo Zancanaro <[email-masked]>
Date: Mon, 26 Nov 2018 22:38:08 +1100
Subject: [PATCH 1/3] gnu: Add ability to restart services on system
 reconfigure

* gnu/services/herd.scm (restart-service): New procedure.
* gnu/services/shepherd.scm (<shepherd-service>)[restart-strategy]: New
  field.
  (always-restart, manually-restart, never-restart): New procedures.
* guix/scripts/system.scm (upgrade-shepherd-services): Automatically restart
  services that should be automatically restarted, and print a message about
  manually restarting services that should be manually restarted.

Temporary commit
---
 gnu/services/herd.scm     |  5 +++++
 gnu/services/shepherd.scm | 25 ++++++++++++++++++++++++-
 guix/scripts/system.scm   | 37 +++++++++++++++++++++++++------------
 3 files changed, 54 insertions(+), 13 deletions(-)

diff --git a/gnu/services/herd.scm b/gnu/services/herd.scm
index 8ff817759..c8d6eb04e 100644
--- a/gnu/services/herd.scm
+++ b/gnu/services/herd.scm
@@ -52,6 +52,7 @@
             load-services
             load-services/safe
             start-service
+            restart-service
             stop-service))
 
 ;;; Commentary:
@@ -256,6 +257,10 @@ when passed a service with an already-registered name."
   (with-shepherd-action name ('start) result
     result))
 
+(define (restart-service name)
+  (with-shepherd-action name ('restart) result
+    result))
+
 (define (stop-service name)
   (with-shepherd-action name ('stop) result
     result))
diff --git a/gnu/services/shepherd.scm b/gnu/services/shepherd.scm
index 49d08cc30..f7e690fb0 100644
--- a/gnu/services/shepherd.scm
+++ b/gnu/services/shepherd.scm
@@ -44,12 +44,17 @@
             shepherd-service-provision
             shepherd-service-canonical-name
             shepherd-service-requirement
+            shepherd-service-restart-strategy
             shepherd-service-respawn?
             shepherd-service-start
             shepherd-service-stop
             shepherd-service-auto-start?
             shepherd-service-modules
 
+            always-restart
+            manually-restart
+            never-restart
+
             shepherd-action
             shepherd-action?
             shepherd-action-name
@@ -141,6 +146,22 @@ DEFAULT is given, use it as the service's default value."
     (guix build utils)
     (guix build syscalls)))
 
+(define (always-restart service)
+  "Unconditionally restart SERVICE and return #f."
+  (let ((name (shepherd-service-canonical-name service)))
+    (info (G_ "restarting service: ~a~%") name)
+    (restart-service name)
+    #f))
+
+(define (manually-restart service)
+  "Do not restart SERVICE, but return #t to indicate that the user should
+restart it."
+  #t)
+
+(define (never-restart service)
+  "Do not restart SERVICE and return #f."
+  #f)
+
 (define-record-type* <shepherd-service>
   shepherd-service make-shepherd-service
   shepherd-service?
@@ -159,7 +180,9 @@ DEFAULT is given, use it as the service's default value."
   (auto-start?   shepherd-service-auto-start?          ;Boolean
                  (default #t))
   (modules       shepherd-service-modules              ;list of module names
-                 (default %default-modules)))
+                 (default %default-modules))
+  (restart-strategy shepherd-service-restart-strategy  ;procedure
+                    (default manually-restart)))
 
 (define-record-type* <shepherd-action>
   shepherd-action make-shepherd-action
diff --git a/guix/scripts/system.scm b/guix/scripts/system.scm
index d92ec7d5a..26e35fe99 100644
--- a/guix/scripts/system.scm
+++ b/guix/scripts/system.scm
@@ -355,16 +355,14 @@ bring the system down."
 
         (with-monad %store-monad
           (munless (null? new-services)
-            (let ((new-service-names  (map shepherd-service-canonical-name new-services))
-                  (to-restart-names   (map shepherd-service-canonical-name to-restart))
-                  (to-start           (filter shepherd-service-auto-start? new-services)))
-              (info (G_ "loading new services:~{ ~a~}...~%") new-service-names)
-              (unless (null? to-restart-names)
-                ;; Listing TO-RESTART-NAMES in the message below wouldn't help
-                ;; because many essential services cannot be meaningfully
-                ;; restarted.  See <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=22039#30>.
-                (format #t (G_ "To complete the upgrade, run 'herd restart SERVICE' to stop,
-upgrade, and restart each service that was not automatically restarted.\n")))
+            (let* ((new-service-names (map shepherd-service-canonical-name new-services))
+                   (to-restart-names  (map shepherd-service-canonical-name to-restart))
+                   (to-start-names    (map shepherd-service-canonical-name
+                                           (filter (lambda (service)
+                                                     (and (shepherd-service-auto-start? service)
+                                                          (not (member service to-restart))))
+                                                   new-services))))
+
               (mlet %store-monad ((files (mapm %store-monad
                                                (compose lower-object
                                                         shepherd-service-file)
@@ -372,10 +370,25 @@ upgrade, and restart each service that was not automatically restarted.\n")))
                 ;; Here we assume that FILES are exactly those that were computed
                 ;; as part of the derivation that built OS, which is normally the
                 ;; case.
+                (info (G_ "loading new services:~{ ~a~}~%") new-service-names)
                 (load-services/safe (map derivation->output-path files))
 
-                (for-each start-service
-                          (map shepherd-service-canonical-name to-start))
+                (info (G_ "starting services:~{ ~a~}~%") to-start-names)
+                (for-each (lambda (service-name)
+                            (info (G_ "starting service: ~a~%") service-name)
+                            (start-service service-name))
+                          to-start-names)
+
+                (let* ((to-manually-restart (filter (lambda (service)
+                                                      ((shepherd-service-restart-strategy service)
+                                                       service))
+                                                    to-restart))
+                       (to-manually-restart-names (map shepherd-service-canonical-name
+                                                       to-manually-restart)))
+                  (unless (null? to-manually-restart-names)
+                    (info (G_ "To complete the upgrade, the following services need to be manually restarted:~{ ~a~}~%")
+                          to-manually-restart-names)))
+
                 (return #t)))))))))
 
 (define* (switch-to-system os
-- 
2.19.2

>From 270a126c6efd498798bb9342a12c0f671df51b4c Mon Sep 17 00:00:00 2001
From: Carlo Zancanaro <[email-masked]>
Date: Mon, 26 Nov 2018 22:38:18 +1100
Subject: [PATCH 2/3] system: Add --restart-services flag for reconfigure

* gnu/services/shepherd.scm (always-restart, manually-restart, never-restart):
  Add restart-services? argument.
* guix/scripts/system.scm (upgrade-shepherd-services): Add parameter to
  automatically restart services marked as needing manual restart.
  (switch-to-system, perform-action, process-action): Pass through
  restart-services? flag.
  (%options): Add --restart-services flag.
  (%default-options): Add #f as default value for --restart-services flag.
---
 gnu/services/shepherd.scm | 14 ++++++++------
 guix/scripts/system.scm   | 23 +++++++++++++++--------
 2 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/gnu/services/shepherd.scm b/gnu/services/shepherd.scm
index f7e690fb0..638f6440c 100644
--- a/gnu/services/shepherd.scm
+++ b/gnu/services/shepherd.scm
@@ -146,19 +146,21 @@ DEFAULT is given, use it as the service's default value."
     (guix build utils)
     (guix build syscalls)))
 
-(define (always-restart service)
+(define (always-restart service restart-services?)
   "Unconditionally restart SERVICE and return #f."
   (let ((name (shepherd-service-canonical-name service)))
     (info (G_ "restarting service: ~a~%") name)
     (restart-service name)
     #f))
 
-(define (manually-restart service)
-  "Do not restart SERVICE, but return #t to indicate that the user should
-restart it."
-  #t)
+(define (manually-restart service restart-services?)
+  "Restart SERVICE and return #f if RESTART-SERVICES? is true, otherwise return #t to
+indicate that the user should manually restart SERVICE."
+  (if restart-services?
+      (always-restart service #t)
+      #t))
 
-(define (never-restart service)
+(define (never-restart service restart-services?)
   "Do not restart SERVICE and return #f."
   #f)
 
diff --git a/guix/scripts/system.scm b/guix/scripts/system.scm
index 26e35fe99..7c2699065 100644
--- a/guix/scripts/system.scm
+++ b/guix/scripts/system.scm
@@ -332,7 +332,7 @@ unload."
        (warning (G_ "failed to obtain list of shepherd services~%"))
        (return #f)))))
 
-(define (upgrade-shepherd-services os)
+(define (upgrade-shepherd-services os restart-services?)
   "Upgrade the Shepherd (PID 1) by unloading obsolete services and loading new
 services specified in OS and not currently running.
 
@@ -381,7 +381,8 @@ bring the system down."
 
                 (let* ((to-manually-restart (filter (lambda (service)
                                                       ((shepherd-service-restart-strategy service)
-                                                       service))
+                                                       service
+                                                       restart-services?))
                                                     to-restart))
                        (to-manually-restart-names (map shepherd-service-canonical-name
                                                        to-manually-restart)))
@@ -391,7 +392,7 @@ bring the system down."
 
                 (return #t)))))))))
 
-(define* (switch-to-system os
+(define* (switch-to-system os restart-services?
                            #:optional (profile %system-profile))
   "Make a new generation of PROFILE pointing to the directory of OS, switch to
 it atomically, and then run OS's activation script."
@@ -419,7 +420,7 @@ it atomically, and then run OS's activation script."
         (primitive-load (derivation->output-path script))))
 
       ;; Finally, try to update system services.
-      (upgrade-shepherd-services os))))
+      (upgrade-shepherd-services os restart-services?))))
 
 (define-syntax-rule (unless-file-not-found exp)
   (catch 'system-error
@@ -827,7 +828,8 @@ and TARGET arguments."
                          use-substitutes? bootloader-target target
                          image-size file-system-type full-boot?
                          (mappings '())
-                         (gc-root #f))
+                         (gc-root #f)
+                         (restart-services? #f))
   "Perform ACTION for OS.  INSTALL-BOOTLOADER? specifies whether to install
 bootloader; BOOTLOADER-TAGET is the target for the bootloader; TARGET is the
 target root directory; IMAGE-SIZE is the size of the image to be built, for
@@ -909,7 +911,7 @@ static checks."
           (case action
             ((reconfigure)
              (mbegin %store-monad
-               (switch-to-system os)
+               (switch-to-system os restart-services?)
                (mwhen install-bootloader?
                  (install-bootloader bootloader-script
                                      #:bootcfg bootcfg
@@ -1092,6 +1094,9 @@ Some ACTIONS support additional ARGS.\n"))
          (option '(#\r "root") #t #f
                  (lambda (opt name arg result)
                    (alist-cons 'gc-root arg result)))
+         (option '("restart-services") #f #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'restart-services? #t result)))
          %standard-build-options))
 
 (define %default-options
@@ -1106,7 +1111,8 @@ Some ACTIONS support additional ARGS.\n"))
     (verbosity . 0)
     (file-system-type . "ext4")
     (image-size . guess)
-    (install-bootloader? . #t)))
+    (install-bootloader? . #t)
+    (restart-services? . #f)))
 
 
 ;;;
@@ -1179,7 +1185,8 @@ resulting from command-line parsing."
                              #:install-bootloader? bootloader?
                              #:target target
                              #:bootloader-target bootloader-target
-                             #:gc-root (assoc-ref opts 'gc-root)))))
+                             #:gc-root (assoc-ref opts 'gc-root)
+                             #:restart-services? (assoc-ref opts 'restart-services?)))))
         #:system system))
     (warn-about-disk-space)))
 
-- 
2.19.2

>From 2077919dca604c94b09cf105c33987daa8c46304 Mon Sep 17 00:00:00 2001
From: Carlo Zancanaro <[email-masked]>
Date: Mon, 26 Nov 2018 22:38:26 +1100
Subject: [PATCH 3/3] services: Always restart guix daemon

* gnu/services/base.scm (guix-shepherd-service): Add restart-strategy of
  always-restart.
---
 gnu/services/base.scm | 1 +
 1 file changed, 1 insertion(+)

diff --git a/gnu/services/base.scm b/gnu/services/base.scm
index 228d3c592..37d60720d 100644
--- a/gnu/services/base.scm
+++ b/gnu/services/base.scm
@@ -1573,6 +1573,7 @@ failed to register hydra.gnu.org public key: ~a~%" status))))))))
            (documentation "Run the Guix daemon.")
            (provision '(guix-daemon))
            (requirement '(user-processes))
+           (restart-strategy always-restart)
            (modules '((srfi srfi-1)))
            (start
             #~(make-forkexec-constructor
-- 
2.19.2