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On Linux each network device *can* (but not necessarily *does*) have an attribute called phys_port_id which can be read from the file of that name in the netdev's sysfs directory. The examples I've seen have been a many-digit hexadecimal number (as an ASCII string). This value can be useful when a single PCI device is associated with multiple netdevs (e.g a dual port Mellanox SR-IOV NIC - this card has a single PCI Physical Function (PF), and that PF has two netdevs associated with it (the "net" subdirectory of the PF in sysfs has two links rather than the usual single link to a netdev directory). Each of the PF netdevs has a different phys_port_id. The Virtual Functions (VF) are similar - the PF (a PCI device) has "n" VFs (also each of these is a PCI device), each VF has two netdevs, and each of the VF netdevs points back to the VF PCI device (with the "device" entry in its sysfs directory) as well as having a phys_port_id matching the PF netdev it is associated with. virNetDevGetPhysPortID() simply attempts to read the phys_port_id for the given netdev and return it to the caller. If this particular netdev driver doesn't support phys_port_id, it returns NULL (*not* a NULL-terminated string, but a NULL pointer) but still counts it as a success.
libvirt library code README
===========================
The directory provides the bulk of the libvirt codebase. Everything
except for the libvirtd daemon and client tools. The build uses a
large number of libtool convenience libraries - one for each child
directory, and then links them together for the final libvirt.so,
although some bits get linked directly to libvirtd daemon instead.
The files directly in this directory are supporting the public API
entry points & data structures.
There are two core shared modules to be aware of:
* util/ - a collection of shared APIs that can be used by any
code. This directory is always in the include path
for all things built
* conf/ - APIs for parsing / manipulating all the official XML
files used by the public API. This directory is only
in the include path for driver implementation modules
* vmx/ - VMware VMX config handling (used by esx/ and vmware/)
Then there are the hypervisor implementations:
* bhyve - bhyve - The BSD Hypervisor
* esx/ - VMware ESX and GSX support using vSphere API over SOAP
* hyperv/ - Microsoft Hyper-V support using WinRM
* lxc/ - Linux Native Containers
* openvz/ - OpenVZ containers using cli tools
* phyp/ - IBM Power Hypervisor using CLI tools over SSH
* qemu/ - QEMU / KVM using qemu CLI/monitor
* remote/ - Generic libvirt native RPC client
* test/ - A "mock" driver for testing
* uml/ - User Mode Linux
* vbox/ - Virtual Box using native API
* vmware/ - VMware Workstation and Player using the vmrun tool
* xen/ - Xen using hypercalls, XenD SEXPR & XenStore
* xenapi/ - Xen using libxenserver
Finally some secondary drivers that are shared for several HVs.
Currently these are used by LXC, OpenVZ, QEMU, UML and Xen drivers.
The ESX, Hyper-V, Power Hypervisor, Remote, Test & VirtualBox drivers all
implement the secondary drivers directly
* cpu/ - CPU feature management
* interface/ - Host network interface management
* network/ - Virtual NAT networking
* nwfilter/ - Network traffic filtering rules
* node_device/ - Host device enumeration
* secret/ - Secret management
* security/ - Mandatory access control drivers
* storage/ - Storage management drivers
Since both the hypervisor and secondary drivers can be built as
dlopen()able modules, it is *FORBIDDEN* to have build dependencies
between these directories. Drivers are only allowed to depend on
the public API, and the internal APIs in the util/ and conf/
directories