Re: [libvirt PATCH v6 0/5] Add a PCI/PCIe device VPD Capability

Add support for deserializing the binary PCI/PCIe VPD format and exposing VPD resources as XML elements in a new nested capability of PCI/PCIe devices called 'vpd'. The series contains the following incremental changes: * The PCI VPD parser module, in-memory resource representation and tests; * VPD-related helpers added to the virpci module; * VPD capability support: XML serialization/deserialization from/into VPD resource data structures; * Documentation. The VPD format is specified in "I.3. VPD Definitions" in PCI specs (2.2+) and "6.28.1 VPD Format" PCIe 4.0. As section 6.28 in PCIe 4.0 notes, the PCI Local Bus and PCIe VPD formats are binary compatible and PCIe 4.0 merely started incorporating what was already present in PCI specs. Linux kernel exposes a binary blob in the VPD format via sysfs since v2.6.26 (commit 94e6108803469a37ee1e3c92dafdd1d59298602f) which requires a parser to interpret. There are usage scenarios where information such as the board serial number needs to be retrieved from PCI(e) VPD. Projects like Nova can utilize this information for cases which involve virtual interface plugging on SmartNIC DPUs but there may be other scenarios and types of information useful to retrieve from VPD. The fact that the format is binary requires proper parsing instead of substring searching hence the full parser is proposed. Likewise, checksum validation requires proper parsing as well. A usage example is present here: https://review.opendev.org/c/openstack/nova/+/808199 The patch follows a prior discussion on the mailing list which has additional context about the use-case but a narrower proposal: https://listman.redhat.com/archives/libvir-list/2021-May/msg00873.html https://www.mail-archive.com/libvir-list@redhat.com/msg218165.html The new functionality is mostly contained in virpcivpd with a couple of new functions added to virpci. Additionally, the necessary XML serialization/deserialization and glue code is added to expose the VPD capability to external clients as XML. A new capability flag is added along with a new capability in order to allow for filtering of PCI devices with the VPD capability using virsh: virsh nodedev-list --cap vpd sudo virsh nodedev-dumpxml --device pci_dddd_bb_ss_f In this example having the root uid is required in order to access the vpd sysfs entry, therefore, the nodedev XML output will only contain the VPD capability if virsh is run as root. The capability is treated as dynamic due to the presence of read-write sections in the VPD format per PCI/PCIe specs (the idea being that read-write resource fields may potentially be altered by the DPU OS over time independently from the host OS). Unit tests cover the parser functionality (including many possible invalid cases), in-memory representation as well as XML serialization and deserialization. Manual functional testing was performed with 2 DPUs and several other NIC models which expose PCI(e) VPD. Testing have also been performed for devices that do not have VPD or those that expose a VPD capability but exhibit invalid behavior (I/O errors while reading a sysfs entry). v6 changes: * Reworked in-memory data structures according to the feedback from Daniel: virPCIVPDResource is now a struct with nested structures for read-only and read-write parts of the VPD. Custom fields (vendor, system are now stored in GPtrArray instances; * Reworked XML element naming: well-known fields from the spec now have human-readable names. Legacy PICMIG fields and binary fields are omitted as before;