On Tue, 10 Jul 2018 16:02:14 +0800 Yi Min Zhao <zyimin@linux.ibm.com> wrote:
Abstract ======== The PCI representation in QEMU has recently been extended for S390 allowing configuration of zPCI attributes like uid (user-defined identifier) and fid (PCI function identifier). The details can be found here: https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg07262.html
To support the new zPCI feature of the S390 platform, two new XML attributes, @uid and @fid, are introduced for device addresses of type 'pci', i.e.: <hostdev mode='subsystem' type='pci'> <driver name='vfio'/> <source> <address domain='0x0001' bus='0x00' slot='0x00' function='0x0'/> </source> <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0' uid='0x0003' fid='0x00000027'/> </hostdev>
uid and fid are optional attributes. If they are defined by the user, unique values within the guest domain must be used. If they are not specified and the architecture requires them, they are automatically generated with non-conflicting values.
Current implementation is the most seamless one for the user as it unites the address specific data of a PCI device on one XML element. It could accommodate both specifying our special parameters (uid and fid) and re-using standard statements (domain, bus, slot and function) for PCI devices. User can still specify bus/slot/function for the virtualized PCI devices in the XML.
Thus uid/fid act as an extension to the PCI address and are stored in a new structure 'virZPCIDeviceAddress' which is a member of common PCI Address structure. Additionally, two hashtables are used for assignment and reservation of uid/fid.
In support of extending the PCI address, a new PCI address extension flag is introduced. This extension flag allows is not only dedicated for the S390 platform but also other architectures needing certain extensions to PCI address space.
FWIW, from my QEMU POV there's nothing obviously wrong in here, but I'm not familiar with the libvirt code base. So I'll leave this to the libvirt developers.