Re: [libvirt] Question about pci-passthrough

On 07/26/2012 11:53 AM, Shradha Shah wrote: Actually, aside from libvirt setting the MAC address prior to assigning the device to the guest, all the rest of the handling is identical to that of a PCI device. I'm curious why you're setting those yourself. that's really something internal that should only be set when parsing a device defined as <interface type='hostdev'> - this ends up creating entries for both types of devices, a virDomainNetDef and a virDomainHostdevDef, that are tightly intertwined. If you attempt to just allocate your own virDomainHostdevDef and set hostdev->parent.type = VIR_DOMAIN_DEVICE_NET, you will have a "very bad time" (tm). The code assumes that any HostdevDef that has a parent-type != NONE is not a standalone object, but is one that resides within a higher level object (see the definition of _virDomainNetDef, in particular the "virDomainHostdevDef def" that is defined within it). The *only way* to setup one of these objects that will work properly is to create a virDomainNetDef object (e.g. call it "net"), then set net->type = VIR_DOMAIN_NET_TYPE_HOSTDEV, and initialize net->data.hostdev.dev with all the hostdev info, including pointing its "parent back to the original "net". Likewise, the virDomainNetDef that you create *must* be placed on the domain's list of network devices and &net->data.hostdev.def *must* be placed on the domain's list of hostdevs. All of this is handled for you by virDomainNetDefParse (look for the VIR_DOMAIN_NET_TYPE_HOSTDEV case). As to where the decision is made about how to treat the device - for starters, <interface type='hostdev'> devices are never attached by calling the function to do a hostdev attach (qemuDomainAttachHostDevice)directly - they are attached by calling the function that does an attach of a net device (qemuDomainAttachNetDevice) - that function calls networkAllocateActualDevice if necessary (in case it's a type='hostdev' hiding behind a type='network') and then if the "actualType" is hostdev, calls qemuDomainAttachHostDevice to do the rest of the work. qemuDomainAttachHostDevice will call down a couple of levels to qemuPrepareHostdevPCIDevices, which will check for hostdev->parent.type == VIR_DOMAIN_DEVICE_NET, and if so will call qemuDomainHostdevNetConfigReplace, which calls the functions that do the netdev-specific setup (i.e. setting the MAC address, although I plan to also add support for setting the VLAN tag). So, a more organized version of this: 1) if you want a hybrid netdev/hostdev, start by creating a virDomainNetDef and filling in the hostdev part, not vice versa, and make sure the corresponding parts are on their respective lists for the domain. (hostdevs and nets) 2) to attach/detach any of these devices, call the *net* version of the attach/detach functions, not the hostdev version. 3) The place that checks if a particular device is a network-type of hostdev, is qemuPrepareHostdevPCIDevices - look for "hostdev->parent.type == VIR_DOMAIN_DEVICE_NET" in that function and follow the call chain down from there to where the action is.