Arch Linux

* In PKGBUILD:
- description of optdepend bridge-utils is: "for briged networking (default)", while NAT really is [1][2]; so the descriptions should be changed to reflect that (affects bridge-utils, dnsmasq and ebtables);
- ebtables and dnsmasq are __required__ for the default networking mode to work [3][4], but their descriptions doesn't reflect it either (say "dnsmasq: for NAT/DHCP for guests" and "ebtables: for networking"); adding a "required for default networking" could be helpful;
- more importantly, libvirtd.service cannot START without qemu installed (which desn't qualify it as an __optional__ dependency I guess); already reported in  FS#41187  but closed. If another hypervisor is to be installed (lxc, usermode, xen) it should also be added in optdepends and referred to as *required*.

* In libvirt.install:
- post_install() script refers to the wiki page (https://wiki.archlinux.org/index.php/Libvirt) which is currently rather messy (accuracy flag set on https://wiki.archlinux.org/index.php/Libvirt#Run_daemon);
- post_upgrade() says that "libvirt runs qemu from nobody:nobody by default" while it runs it from nobody:**kvm** (confirmed in  FS#41382 ), and it seems that if the group is changed to something else (like "qemu" or "libvirt") then KVM access throws error (see https://wiki.archlinux.org/index.php/Libvirt#Run_daemon as well).

[1] http://wiki.libvirt.org/page/VirtualNetworking#The_default_configuration
[2] http://wiki.libvirt.org/page/Networking#NAT_forwarding_.28aka_.22virtual_networks.22.29
[3] http://wiki.libvirt.org/page/Libvirtd_and_dnsmasq
[4] https://bugs.archlinux.org/task/41187

Additional info:
* package version(s): libvirt-1.2.8-1, virt-manager-1.1.0-1, virt-viewer-0.6.0-3

Steps to reproduce:
# pacman -S libvirt virt-manager virtviewer
# chown -R nobody:kvm /var/{run,lib,cache}/libvirt/qemu /var/lib/libvirt/images ### as per wiki
chown: incorrect group: « nobody:kvm »
# systemctl start libvirtd.service
# systemctl status libvirtd.service
* libvirtd.service - Virtualization daemon
Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; disabled)
Active: inactive (dead)
Docs: man:libvirtd(8)
http://libvirt.org

libvirtd[5208]: libvirt version: 1.2.8
libvirtd[5208]: Cannot check dnsmasq binary /sbin/dnsmasq: No such file or directory
libvirtd[5208]: direct firewall backend requested, but /sbin/ebtables is not available: No such file or directory
libvirtd[5208]: internal error: Failed to find path for dmidecode binary
libvirtd[5208]: invalid argument: Failed to parse group 'kvm'
libvirtd[5208]: Initialisation of QEMU state driver failed: invalid argument: Failed to parse group 'kvm'
libvirtd[5208]: Driver state initialisation failed

# virsh sysinfo
error: failed to connect to the hypervisor
error: no valid connection
error: Failed to connect socket to '/var/run/libvirt/libvirt-sock': No such file or directory

# virt-manager
--> error saying it cannot connect via qemu:///system

# pacman -S qemu
# systemctl start libvirtd.service
# systemctl status libvirtd.service
● libvirtd.service - Virtualization daemon
Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; disabled)
Active: active (running) since mar. 2014-09-09 14:46:46 CEST; 2s ago
Docs: man:libvirtd(8)
http://libvirt.org
Main PID: 18580 (libvirtd)
CGroup: /system.slice/libvirtd.service
└─18580 /usr/bin/libvirtd -p /var/run/libvirtd.pid

libvirtd[18580]: libvirt version: 1.2.8
libvirtd[18580]: Cannot check dnsmasq binary /sbin/dnsmasq: No such file or directory
libvirtd[18580]: direct firewall backend requested, but /sbin/ebtables is not available: No such file or directory
libvirtd[18580]: internal error: Failed to find path for dmidecode binary
libvirtd[18580]: internal error: Failed to find path for dmidecode binary
libvirtd[18580]: Unable to delete bridge virbr0: Device or resource busy

# chown -R nobody:kvm /var/{run,lib,cache}/libvirt/qemu /var/lib/libvirt/images

*** Networking part ***
# virsh net-list
Name State Autostart Persistent
----------------------------------------------------------

# pacman -S --asdeps ebtables
# systemctl restart libvirtd.service
# systemctl status libvirtd
● libvirtd.service - Virtualization daemon
Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; disabled)
Active: active (running) since mar. 2014-09-09 14:59:43 CEST; 2min 11s ago
Docs: man:libvirtd(8)
http://libvirt.org
Main PID: 18996 (libvirtd)
CGroup: /system.slice/libvirtd.service
└─18996 /usr/bin/libvirtd -p /var/run/libvirtd.pid

libvirtd[18996]: libvirt version: 1.2.8
libvirtd[18996]: Cannot check dnsmasq binary /sbin/dnsmasq: No such file or directory
libvirtd[18996]: internal error: Failed to find path for dmidecode binary
libvirtd[18996]: internal error: Failed to find path for dmidecode binary
libvirtd[18996]: Unable to create bridge virbr0: File exists

# virsh net-list
Name State Autostart Persistent
----------------------------------------------------------

# systemctl reboot
...
--> Need to install dnsmasq as well for default NATed virtual network to work.

Suggestions:
1. Make qemu required dependency
2. add in optdepends that ebtables and dnsmasq are REQUIRED for the DEFAULT NATed virtual networking
3. remove mention of "default" for bridge-utils
4. somebody knowledgeable enough update the wiki (I'm already preparing an overhaul but I'm no libvirt/qemu/kvm guru)
5. change post_install() to say "...nobody:kvm" and "change the group with caution" (the user's alright)

Example PKGBUILD and libvirt.install integrating suggestions attached