services: libvirt: Add configurable service requirements.

This enhances flexibility by allowing users to specify custom service
dependencies for libvirt, rather than being limited to the default hardcoded
requirements. This is particularly useful for complex deployments or when
integrating with custom service configurations.

Note that default 'dbus-system' requirement may not be strictly necessary for
basic libvirt operation. For instance, libvirt can function without issues in
many cases even when dbus-system is not included in the requirements, allowing
for more minimal deployments.

* gnu/services/virtualization.scm (list-of-symbols?,
serialize-list-of-symbols): New procedures.
(libvirt-configuration): Add 'requirement' field to allow custom service
dependencies.
(libvirt-shepherd-service): Use the configured requirements instead of
hardcoded ones.
* doc/guix.texi (Virtualization Services): Document the new 'requirement'
option.

Change-Id: I05cfbb5227cff9b7d9b55ee37774c96e39c4c526

1 files changed, 11 insertions, 1 deletions

diff --git a/gnu/services/virtualization.scm b/gnu/services/virtualization.scm
index f369c29c76d..06524f7851d 100644
--- a/gnu/services/virtualization.scm
+++ b/gnu/services/virtualization.scm
@@ -135,6 +135,7 @@
             libvirt-configuration-ovs-timeout
             libvirt-configuration-prio-workers
             libvirt-configuration-qemu
+            libvirt-configuration-requirement
             libvirt-configuration-sasl-allowed-usernames
             libvirt-configuration-tcp-port
             libvirt-configuration-tls-allowed-dn-list
@@ -214,6 +215,12 @@
 (define list-of-file-likes?
   (list-of file-like?))
 
+(define list-of-symbols?
+  (list-of symbol?))
+
+(define (serialize-list-of-symbols field-name val)
+  val)
+
 (define-configuration libvirt-configuration
   (libvirt
    (file-like libvirt)
@@ -224,6 +231,9 @@
   (dmidecode
    (file-like dmidecode)
    "The Dmidecode package to use.")
+  (requirement
+   (list-of-symbols '(dbus-system))
+   "Shepherd services dependencies to the provisioned Shepherd service.")
   (firmwares
    (list-of-file-likes (list ovmf-x86-64))
    "List of UEFI/BIOS firmware packages to make available.  Each firmware
@@ -495,7 +505,7 @@ avoid potential infinite waits blocking libvirt."))
     (list (shepherd-service
            (documentation "Run the libvirt daemon.")
            (provision '(libvirtd))
-           (requirement '(dbus-system))
+           (requirement (libvirt-configuration-requirement config))
            (start #~(make-forkexec-constructor
                      (list (string-append #$libvirt "/sbin/libvirtd")
                            "-f" #$config-file