bug#58084: guix deploy fails, leaving the newly installed system generation active

["Ludovic Courtès" <ludo@gnu.org>]

Hi,

Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:

> While attempting to deploy to overdrive1, using the 9971141 commit in
> the maintenance repo, I encountered the following error:
>
> maxim@hurd ~/src/guix-maintenance/hydra$ guix time-machine --commit=08d515233241ee0921b8b5ab706f98170c62437c -- deploy -L modules deploy-overdrive1.scm
> The following 1 machine will be deployed:
>   overdrive1
>
> guix deploy: deploying to overdrive1...
> guix deploy: sending 0 store items (0 MiB) to 'overdrive1.guix.gnu.org'...
> guix deploy: sending 0 store items (0 MiB) to 'overdrive1.guix.gnu.org'...
> guix deploy: sending 0 store items (0 MiB) to 'overdrive1.guix.gnu.org'...
> guix deploy: error: failed to deploy overdrive1: failed to switch systems while deploying 'overdrive1':
> system-error "symlink" "~A" ("File exists") (17)

I can reproduce it.

The failing code is in /gnu/store/…-switch-to-system.scm:

--8<---------------cut here---------------start------------->8---
(begin
  (use-modules
   (guix config)
   (guix profiles)
   (guix utils))
  (define profile
    (or #f
	(string-append %state-directory "/profiles/system")))
  (let*
      ((number
	(#{1+}
	 #
	 (generation-number profile)))
       (generation
	(generation-file-name profile number)))
    (switch-symlinks generation "/gnu/store/kifxq4hmp4ihn6nb06ia8wms33qrndxn-system")
    (switch-symlinks profile generation)
    (setenv "GUIX_NEW_SYSTEM" "/gnu/store/kifxq4hmp4ihn6nb06ia8wms33qrndxn-system")
    (primitive-load "/gnu/store/1wdwlaqkmixb1d7by7fj23lxppw8x44r-activate.scm")))
--8<---------------cut here---------------end--------------->8---

We can run it manually to get debugging data:

--8<---------------cut here---------------start------------->8---
ludo@overdrive1 ~$ sudo -E env -i COLUMNS=100  "/gnu/store/xv7j4im9ap92mv0mbsm1wa4px93zxrms-switch-to-system.scm"
making '/gnu/store/kifxq4hmp4ihn6nb06ia8wms33qrndxn-system' the current system...
WARNING: (guile-user): imported module (guix build utils) overrides core binding `delete'
setting up setuid programs in '/run/setuid-programs'...
populating /etc from /gnu/store/hf3qxlaiajvapwis0lq20avgl2whfa5w-etc...
Backtrace:
           6 (primitive-load "/gnu/store/xv7j4im9ap92mv0mbsm1wa4px93zxrms-switch-to-system.scm")
           5 (primitive-load "/gnu/store/1wdwlaqkmixb1d7by7fj23lxppw8x44r-activate.scm")
In ice-9/boot-9.scm:
   260:13  4 (for-each #<procedure primitive-load (_)> _)
In unknown file:
           3 (primitive-load "/gnu/store/v03vaksmkpj7wv4dhm0yrd3y65lzbixz-activate-service.scm")
In srfi/srfi-1.scm:
    634:9  2 (for-each #<procedure ffffaaff10e0 at gnu/build/activation.scm:257:12 (file)> _)
In gnu/build/activation.scm:
   267:20  1 (_ "modprobe.d")
In unknown file:
           0 (symlink "/etc/static/modprobe.d" "/etc/modprobe.d")

ERROR: In procedure symlink:
In procedure symlink: File exists
--8<---------------cut here---------------end--------------->8---

This is because ‘zram-device-service-type’ contributes a file to
/etc/modprobe.d:

--8<---------------cut here---------------start------------->8---
(define %zram-device-config
  `("modprobe.d/zram.conf"
    ,(plain-file "zram.conf"
                 "options zram num_devices=1")))

(define zram-device-service-type
  (service-type
    (name 'zram)
    (default-value (zram-device-configuration))
    (extensions
      (list (service-extension kernel-module-loader-service-type
                               (const (list "zram")))
            (service-extension etc-service-type
                               (const (list %zram-device-config)))
            (service-extension udev-service-type
                               (compose list zram-device-udev-rule))))
    (description "Creates a zram swap device.")))
--8<---------------cut here---------------end--------------->8---

… which is fine, except that there was already a pre-existing
/etc/modprobe.d directory (coming from openSuSE, the distro that was
initially installed on this machine), which caused this activation code
to break:

--8<---------------cut here---------------start------------->8---
ludo@overdrive1 ~$ ls -l /etc/modprobe.d
total 36
-rw-r--r-- 1 root root 3221 Nov  6  2016 00-system.conf
-rw-r--r-- 1 root root  532 Nov 14  2012 10-unsupported-modules.conf
-rw-r--r-- 1 root root  181 May  5  2017 50-alsa.conf
-rw-r--r-- 1 root root 5009 Sep 15  2016 50-blacklist.conf
-rw-r--r-- 1 root root  128 Oct 12  2017 50-bluetooth.conf
-rw-r--r-- 1 root root   33 Oct 20  2016 50-ipw2200.conf
-rw-r--r-- 1 root root   34 Oct 20  2016 50-iwl3945.conf
-rw-r--r-- 1 root root   47 Nov 22  2011 99-local.conf
ludo@overdrive1 ~$ ls -ld /etc/modprobe.d
drwxr-xr-x 1 root root 260 Jan 29  2018 /etc/modprobe.d/
--8<---------------cut here---------------end--------------->8---

Once moved out of the way, reconfiguration proceeds just fine and
happiness ensues:

--8<---------------cut here---------------start------------->8---
ludo@overdrive1 ~$ ls -l /etc/modprobe.d
lrwxrwxrwx 1 root root 22 Sep 26 17:19 /etc/modprobe.d -> /etc/static/modprobe.d
ludo@overdrive1 ~$ ls -l /etc/modprobe.d/
total 4
lrwxrwxrwx 1 root root 53 Jan  1  1970 zram.conf -> /gnu/store/srl5xij6hf4x6iksx98grb1spcj3rch1-zram.conf
--8<---------------cut here---------------end--------------->8---

Ludo’.