Patch from NixOS: 
https://raw.githubusercontent.com/NixOS/nixpkgs/b98031a49c66095dd1eb9185ecdaeeb5e3cd752d/pkgs/development/libraries/libvirt/0001-meson-patch-in-an-install-prefix-for-building-on-nix.patch

From a896b0be849455edb83a9305dfec9b41447ef3e4 Mon Sep 17 00:00:00 2001
From: Euan Kemp <euank@euank.com>
Date: Thu, 14 Jan 2021 00:32:00 -0800
Subject: [PATCH] meson: patch in an install prefix for building on nix

Used in the nixpkgs version of libvirt so that we can install things in
the nix store, but read them from the root filesystem.
---
 meson.build                       |  9 +++++++++
 meson_options.txt                 |  2 ++
 src/libxl/meson.build             |  6 +++---
 src/locking/meson.build           |  8 ++++----
 src/lxc/meson.build               |  6 +++---
 src/meson.build                   | 18 +++++++++---------
 src/network/meson.build           | 12 ++++++------
 src/nwfilter/xml/meson.build      |  2 +-
 src/qemu/meson.build              | 14 +++++++-------
 src/remote/meson.build            |  6 +++---
 src/security/apparmor/meson.build |  8 ++++----
 tools/meson.build                 |  4 ++--
 12 files changed, 53 insertions(+), 42 deletions(-)

diff --git a/meson.build b/meson.build
index b5164f6..33719f1 100644
--- a/meson.build
+++ b/meson.build
@@ -39,6 +39,8 @@ if host_machine.system() == 'windows'
   conf.set('WINVER', '0x0600') # Win Vista / Server 2008
 endif
 
+# patched in for nix
+install_prefix = get_option('install_prefix')
 
 # set various paths
 
@@ -57,6 +59,13 @@ else
   sysconfdir = prefix / get_option('sysconfdir')
 endif
 
+# nix: don't prefix the localstatedir; some things need to write to it, so it
+# can't be in the nix store, and that's what the prefix is.
+# We'll prefix things ourselves where needed
+localstatedir = get_option('localstatedir')
+# Same for sysconfidr
+sysconfdir = get_option('sysconfdir')
+
 # if --prefix is /usr, don't use /usr/var for localstatedir or /usr/etc for
 # sysconfdir as this makes a lot of things break in testing situations
 if prefix == '/usr'
diff --git a/meson_options.txt b/meson_options.txt
index e5d79c2..081cd32 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -1,3 +1,5 @@
+option('install_prefix', type: 'string', value: '', description: 'prefix for nix store installation')
+
 option('no_git', type: 'boolean', value: false, description: 'Disable git submodule update')
 option('packager', type: 'string', value: '', description: 'Extra packager name')
 option('packager_version', type: 'string', value: '', description: 'Extra packager version')
diff --git a/src/libxl/meson.build b/src/libxl/meson.build
index 3bb6cc5..78d7be0 100644
--- a/src/libxl/meson.build
+++ b/src/libxl/meson.build
@@ -84,8 +84,8 @@ if conf.has('WITH_LIBXL')
   }
 
   virt_install_dirs += [
-    localstatedir / 'lib' / 'libvirt' / 'libxl',
-    runstatedir / 'libvirt' / 'libxl',
-    localstatedir / 'log' / 'libvirt' / 'libxl',
+    install_prefix + localstatedir / 'lib' / 'libvirt' / 'libxl',
+    install_prefix + runstatedir / 'libvirt' / 'libxl',
+    install_prefix + localstatedir / 'log' / 'libvirt' / 'libxl',
   ]
 endif
diff --git a/src/locking/meson.build b/src/locking/meson.build
index 8a28310..9da81cc 100644
--- a/src/locking/meson.build
+++ b/src/locking/meson.build
@@ -243,14 +243,14 @@ if conf.has('WITH_LIBVIRTD')
   }
 
   virt_install_dirs += [
-    localstatedir / 'lib' / 'libvirt' / 'lockd',
-    localstatedir / 'lib' / 'libvirt' / 'lockd' / 'files',
-    runstatedir / 'libvirt' / 'lockd',
+    install_prefix + localstatedir / 'lib' / 'libvirt' / 'lockd',
+    install_prefix + localstatedir / 'lib' / 'libvirt' / 'lockd' / 'files',
+    install_prefix + runstatedir / 'libvirt' / 'lockd',
   ]
 
   if conf.has('WITH_SANLOCK')
     virt_install_dirs += [
-      localstatedir / 'lib' / 'libvirt' / 'sanlock',
+      install_prefix + localstatedir / 'lib' / 'libvirt' / 'sanlock',
     ]
   endif
 endif
diff --git a/src/lxc/meson.build b/src/lxc/meson.build
index f8e2a88..96d6687 100644
--- a/src/lxc/meson.build
+++ b/src/lxc/meson.build
@@ -182,8 +182,8 @@ if conf.has('WITH_LXC')
   }
 
   virt_install_dirs += [
-    localstatedir / 'lib' / 'libvirt' / 'lxc',
-    runstatedir / 'libvirt' / 'lxc',
-    localstatedir / 'log' / 'libvirt' / 'lxc',
+    install_prefix + localstatedir / 'lib' / 'libvirt' / 'lxc',
+    install_prefix + runstatedir / 'libvirt' / 'lxc',
+    install_prefix + localstatedir / 'log' / 'libvirt' / 'lxc',
   ]
 endif
diff --git a/src/meson.build b/src/meson.build
index 7c47821..d33d16a 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -669,7 +669,7 @@ endforeach
 
 virt_conf_files += 'libvirt.conf'
 
-install_data(virt_conf_files, install_dir: confdir)
+install_data(virt_conf_files, install_dir: install_prefix + confdir)
 install_data(virt_aug_files, install_dir: virt_aug_dir)
 
 # augeas_test_data:
@@ -729,7 +729,7 @@ foreach data : virt_daemon_confs
     output: '@0@.conf'.format(data['name']),
     configuration: daemon_conf,
     install: true,
-    install_dir: confdir,
+    install_dir: install_prefix + confdir,
   )
 
   if data.get('with_ip', false)
@@ -853,14 +853,14 @@ if conf.has('WITH_LIBVIRTD')
 
       install_data(
         init_file,
-        install_dir: sysconfdir / 'init.d',
+        install_dir: install_prefix + sysconfdir / 'init.d',
         rename: [ init['name'] ],
       )
 
       if init.has_key('confd')
         install_data(
           init['confd'],
-          install_dir: sysconfdir / 'conf.d',
+          install_dir: install_prefix + sysconfdir / 'conf.d',
           rename: [ init['name'] ],
         )
       endif
@@ -872,7 +872,7 @@ if init_script != 'none'
   foreach sysconf : sysconf_files
     install_data(
       sysconf['file'],
-      install_dir: sysconfdir / 'sysconfig',
+      install_dir: install_prefix + sysconfdir / 'sysconfig',
       rename: [ sysconf['name'] ],
     )
   endforeach
@@ -897,10 +897,10 @@ endif
 # Install empty directories
 
 virt_install_dirs += [
-  localstatedir / 'cache' / 'libvirt',
-  localstatedir / 'lib' / 'libvirt' / 'images',
-  localstatedir / 'lib' / 'libvirt' / 'filesystems',
-  localstatedir / 'lib' / 'libvirt' / 'boot',
+  install_prefix + localstatedir / 'cache' / 'libvirt',
+  install_prefix + localstatedir / 'lib' / 'libvirt' / 'images',
+  install_prefix + localstatedir / 'lib' / 'libvirt' / 'filesystems',
+  install_prefix + localstatedir / 'lib' / 'libvirt' / 'boot',
 ]
 
 meson.add_install_script(
diff --git a/src/network/meson.build b/src/network/meson.build
index 3ec598c..b02040b 100644
--- a/src/network/meson.build
+++ b/src/network/meson.build
@@ -79,9 +79,9 @@ if conf.has('WITH_NETWORK')
   }
 
   virt_install_dirs += [
-    localstatedir / 'lib' / 'libvirt' / 'network',
-    localstatedir / 'lib' / 'libvirt' / 'dnsmasq',
-    runstatedir / 'libvirt' / 'network',
+    install_prefix + localstatedir / 'lib' / 'libvirt' / 'network',
+    install_prefix + localstatedir / 'lib' / 'libvirt' / 'dnsmasq',
+    install_prefix + runstatedir / 'libvirt' / 'network',
   ]
 
   configure_file(
@@ -89,12 +89,12 @@ if conf.has('WITH_NETWORK')
     output: '@BASENAME@',
     copy: true,
     install: true,
-    install_dir: confdir / 'qemu' / 'networks',
+    install_dir: install_prefix + confdir / 'qemu' / 'networks',
   )
 
   meson.add_install_script(
     meson_python_prog.path(), python3_prog.path(), meson_install_symlink_prog.path(),
-    confdir / 'qemu' / 'networks' / 'autostart',
+    install_prefix + confdir / 'qemu' / 'networks' / 'autostart',
     '../default.xml', 'default.xml',
   )
 
diff --git a/src/nwfilter/xml/meson.build b/src/nwfilter/xml/meson.build
index 0d96c54..66c92a1 100644
--- a/src/nwfilter/xml/meson.build
+++ b/src/nwfilter/xml/meson.build
@@ -25,4 +25,4 @@ nwfilter_xml_files = [
   'qemu-announce-self.xml',
 ]
 
-install_data(nwfilter_xml_files, install_dir: sysconfdir / 'libvirt' / 'nwfilter')
+install_data(nwfilter_xml_files, install_dir: install_prefix + sysconfdir / 'libvirt' / 'nwfilter')
diff --git a/src/qemu/meson.build b/src/qemu/meson.build
index 90640b0..8802cec 100644
--- a/src/qemu/meson.build
+++ b/src/qemu/meson.build
@@ -171,12 +171,12 @@ if conf.has('WITH_QEMU')
   }
 
   virt_install_dirs += [
-    localstatedir / 'lib' / 'libvirt' / 'qemu',
-    runstatedir / 'libvirt' / 'qemu',
-    localstatedir / 'cache' / 'libvirt' / 'qemu',
-    localstatedir / 'log' / 'libvirt' / 'qemu',
-    localstatedir / 'lib' / 'libvirt' / 'swtpm',
-    runstatedir / 'libvirt' / 'qemu' / 'swtpm',
-    localstatedir / 'log' / 'swtpm' / 'libvirt' / 'qemu',
+    install_prefix + localstatedir / 'lib' / 'libvirt' / 'qemu',
+    install_prefix + runstatedir / 'libvirt' / 'qemu',
+    install_prefix + localstatedir / 'cache' / 'libvirt' / 'qemu',
+    install_prefix + localstatedir / 'log' / 'libvirt' / 'qemu',
+    install_prefix + localstatedir / 'lib' / 'libvirt' / 'swtpm',
+    install_prefix + runstatedir / 'libvirt' / 'qemu' / 'swtpm',
+    install_prefix + localstatedir / 'log' / 'swtpm' / 'libvirt' / 'qemu',
   ]
 endif
diff --git a/src/remote/meson.build b/src/remote/meson.build
index 9ad2f6a..429a15b 100644
--- a/src/remote/meson.build
+++ b/src/remote/meson.build
@@ -245,7 +245,7 @@ if conf.has('WITH_REMOTE')
     }
 
     virt_install_dirs += [
-      localstatedir / 'log' / 'libvirt',
+      install_prefix + localstatedir / 'log' / 'libvirt',
     ]
 
     logrotate_conf = configuration_data()
@@ -259,7 +259,7 @@ if conf.has('WITH_REMOTE')
       )
       install_data(
         log_file,
-        install_dir: sysconfdir / 'logrotate.d',
+        install_dir: install_prefix + sysconfdir / 'logrotate.d',
         rename: [ name ],
       )
     endforeach
@@ -309,7 +309,7 @@ endif
 if conf.has('WITH_SASL')
   install_data(
     'libvirtd.sasl',
-    install_dir: sysconfdir / 'sasl2',
+    install_dir: install_prefix + sysconfdir / 'sasl2',
     rename: [ 'libvirt.conf' ],
   )
 endif
diff --git a/src/security/apparmor/meson.build b/src/security/apparmor/meson.build
index af43780..e2d6c81 100644
--- a/src/security/apparmor/meson.build
+++ b/src/security/apparmor/meson.build
@@ -17,22 +17,22 @@ foreach name : apparmor_gen_profiles
     output: name,
     configuration: apparmor_gen_profiles_conf,
     install: true,
-    install_dir: apparmor_dir,
+    install_dir: install_prefix + apparmor_dir,
   )
 endforeach
 
 install_data(
   [ 'libvirt-qemu', 'libvirt-lxc' ],
-  install_dir: apparmor_dir / 'abstractions',
+  install_dir: install_prefix + apparmor_dir / 'abstractions',
 )
 
 install_data(
   [ 'TEMPLATE.qemu', 'TEMPLATE.lxc' ],
-  install_dir: apparmor_dir / 'libvirt',
+  install_dir: install_prefix + apparmor_dir / 'libvirt',
 )
 
 install_data(
   'usr.lib.libvirt.virt-aa-helper.local',
-  install_dir: apparmor_dir / 'local',
+  install_dir: install_prefix + apparmor_dir / 'local',
   rename: 'usr.lib.libvirt.virt-aa-helper',
 )
diff --git a/tools/meson.build b/tools/meson.build
index b8c6802..dacd0ff 100644
--- a/tools/meson.build
+++ b/tools/meson.build
@@ -115,7 +115,7 @@ if conf.has('WITH_LOGIN_SHELL')
     install_rpath: libvirt_rpath,
   )
 
-  install_data('virt-login-shell.conf', install_dir: sysconfdir / 'libvirt')
+  install_data('virt-login-shell.conf', install_dir: install_prefix + sysconfdir / 'libvirt')
 endif
 
 if host_machine.system() == 'windows'
@@ -274,7 +274,7 @@ configure_file(
 if init_script == 'systemd'
   install_data(
     'libvirt-guests.sysconf',
-    install_dir: sysconfdir / 'sysconfig',
+    install_dir: install_prefix + sysconfdir / 'sysconfig',
     rename: 'libvirt-guests',
   )