libvirtd: use nix paths for zfs userspace tools

Libvirt zfs storage driver makes use of zfs userspace tools to get the
neccesary information. This patch sets correct nix store paths for these
tools.

pkgs/development/libraries/libvirt/0002-substitute-zfs-and-zpool-commands.patch

@@ -0,0 +1,27 @@
+From dc5e3df2fd29a547ef0f9545e190a0ce3a73c95c Mon Sep 17 00:00:00 2001
+From: Tako Marks <me@github.tako.mx>
+Date: Tue, 6 Sep 2022 20:19:26 +0200
+Subject: [PATCH] substitute zfs and zpool commands
+
+---
+ src/storage/storage_backend_zfs.c | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/src/storage/storage_backend_zfs.c b/src/storage/storage_backend_zfs.c
+index 2a5d74357d..460b3025c4 100644
+--- a/src/storage/storage_backend_zfs.c
++++ b/src/storage/storage_backend_zfs.c
+@@ -33,8 +33,8 @@
+ 
+ VIR_LOG_INIT("storage.storage_backend_zfs");
+ 
+-#define ZFS "zfs"
+-#define ZPOOL "zpool"
++#define ZFS "@zfs@"
++#define ZPOOL "@zpool@"
+ 
+ /*
+  * Some common flags of zfs and zpool commands we use:
+-- 
+2.36.2
+

pkgs/development/libraries/libvirt/default.nix

@@ -33,6 +33,7 @@
 , readline
 , rpcsvc-proto
 , stdenv
+, substituteAll
 , xhtml1
 , yajl
 , writeScript
@@ -126,6 +127,11 @@ stdenv.mkDerivation rec {
 
   patches = [
     ./0001-meson-patch-in-an-install-prefix-for-building-on-nix.patch
+    (substituteAll {
+      src = ./0002-substitute-zfs-and-zpool-commands.patch;
+      zfs = "${zfs}/bin/zfs";
+      zpool = "${zfs}/bin/zpool";
+    })
   ];
 
   # remove some broken tests