Re: ZFS on Guix

[raid5atemyhomework]

Hi guix-developers,

Another issue here is that ZFS prefers to not be managed via 
`/etc/fstab`/`mount`/`umount`.  Instead, at startup ZFS magically imports ZFS 
pools and mounts ZFS datasets in the correct place, as configured in the 
`mountpoint` properties of the dataset.  This magic is actually implemented by 
executing `zpool import -a` at startup after ZFS module loading.  Note that 
`zpool import -a` has to be executed always so that ZFS can detect its pools, 
though the automatic mounting can be suppressed with `zpool import -a -N`.

(`systemd`-based distros have a number of `systemd` services that handle ZFS 
importation by use of a `/etc/zfs/zpool.cache` file that ZFS maintains, and 
then does `zfs mount -a` to do automounting, but I'll leave that for later.)

Now, properly speaking, the shepherd `file-systems` service should not be 
started until we have actually performed ZFS automounting.  This means that 
`file-systems` has to have as a requirement the ZFS shepherd service that 
implements the automounting.  And of course it should *not* require that if ZFS 
isn't installed in the system.

So, I made another patch that makes the `file-systems` shepherd service have an 
extensible set of requirements, like `user-processes` does.  It's below.  
Actual `file-system`s declared in the operating system then make themselves 
requirements of `file-systems`.  Then, a ZFS automounting shepherd service can 
be installed by the `zfs-service-type` and added as a requirement of the 
`file-systems` shepherd service.

This is important since one possible use of ZFS is to have it provide the 
`/home` filesystem.  And the `/home` filesystem has to be mounted before 
`user-homes` shepherd service starts.  So the ZFS automounting shepherd service 
has to be a requirement of `file-systems`, which is enabled by the below.

Please review!


>From 792a8f8efc95e4fe9a94d42f839ddcfb034b8540 Mon Sep 17 00:00:00 2001
From: raid5atemyhomework <raid5atemyhomework@protonmail.com>
Date: Wed, 6 Jan 2021 08:15:54 +0800
Subject: [PATCH] gnu: Make file-systems target extensible by services.

* gnu/services/base.scm (file-system-shepherd-services): Move file-systems
shepherd service to ...
(file-systems-target-shepherd-services): ... new procedure here.
(file-systems-target-service-type): New variable.
(file-system-service-type): Extend file-systems-target service to add each
file-system as a requirement.
* gnu/system.scm (operating-system-default-essential-services): Instantiate
file-systems-target-service-type.
(hurd-default-essential-services): Instantiate file-systems-target-service-type.
---
 gnu/services/base.scm | 37 +++++++++++++++++++++++++++----------
 gnu/system.scm        |  2 ++
 2 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/gnu/services/base.scm b/gnu/services/base.scm
index 945b546607..13cfb6a8a2 100644
--- a/gnu/services/base.scm
+++ b/gnu/services/base.scm
@@ -13,6 +13,7 @@
 ;;; Copyright © 2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 ;;; Copyright © 2020 Florian Pelz <pelzflorian@pelzflorian.de>
 ;;; Copyright © 2020 Brice Waegeneire <brice@waegenei.re>
+;;; Copyright © 2021 raid5atemyhomework <raid5atemyhomework@protonmail.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -67,6 +68,7 @@
   #:export (fstab-service-type
             root-file-system-service
             file-system-service-type
+            file-systems-target-service-type
             swap-service
             host-name-service
             console-keymap-service
@@ -362,18 +364,29 @@ FILE-SYSTEM."
                        (gnu system file-systems)
                        ,@%default-modules)))))))

+(define (file-systems-target-shepherd-services requirements)
+  (list
+    (shepherd-service
+      (provision '(file-systems))
+      (requirement (cons* 'root-file-system 'user-file-systems requirements))
+      (documentation "Target for all the initially-mounted file systems")
+      (start #~(const #t))
+      (stop #~(const #t)))))
+(define file-systems-target-service-type
+  (service-type
+    (name 'file-systems)
+    (extensions (list (service-extension shepherd-root-service-type
+                                         
file-systems-target-shepherd-services)))
+    (compose concatenate)
+    (extend append)
+    ;; Extensions can add new values to this list.
+    (default-value '())
+    (description "The @code{file-systems} service is the target that is started
+when all file systems have been mounted.")))
+
 (define (file-system-shepherd-services file-systems)
   "Return the list of Shepherd services for FILE-SYSTEMS."
   (let* ((file-systems (filter file-system-mount? file-systems)))
-    (define sink
-      (shepherd-service
-       (provision '(file-systems))
-       (requirement (cons* 'root-file-system 'user-file-systems
-                           (map file-system->shepherd-service-name
-                                file-systems)))
-       (documentation "Target for all the initially-mounted file systems")
-       (start #~(const #t))
-       (stop #~(const #f))))

     (define known-mount-points
       (map file-system-mount-point file-systems))
@@ -403,7 +416,7 @@ FILE-SYSTEM."
                            (filter (negate known?) (mount-points)))
                  #f))))

-    (cons* sink user-unmount
+    (cons* user-unmount
            (map file-system-shepherd-service file-systems))))

 (define (file-system-fstab-entries file-systems)
@@ -431,6 +444,10 @@ FILE-SYSTEM."
                        (service-extension fstab-service-type
                                           file-system-fstab-entries)

+                       ;; Have 'file-systems' depend on each declared file 
system.
+                       (service-extension file-systems-target-service-type
+                                          (cut map 
file-system->shepherd-service-name <>))
+
                        ;; Have 'user-processes' depend on 'file-systems'.
                        (service-extension user-processes-service-type
                                           (const '(file-systems)))))
diff --git a/gnu/system.scm b/gnu/system.scm
index 5c530f176e..6987641ee8 100644
--- a/gnu/system.scm
+++ b/gnu/system.scm
@@ -667,6 +667,7 @@ bookkeeping."
                     (operating-system-setuid-programs os))
            (service profile-service-type
                     (operating-system-packages os))
+           (service file-systems-target-service-type)
            other-fs
            (append mappings swaps

@@ -691,6 +692,7 @@ bookkeeping."
                                    (operating-system-groups os))
                            (operating-system-skeletons os))
           (root-file-system-service)
+          (service file-systems-target-service-type)
           (service file-system-service-type '())
           (service fstab-service-type
                    (filter file-system-needed-for-boot?
--
2.29.2