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The lookup didn't do anything apart from comparing the sysfs paths anyway since that's what makes each mdev unique. The most ridiculous usage of the old logic was in virHostdevReAttachMediatedDevices where in order to drop an mdev hostdev from the list of active devices we first had to create a new mdev and use it in the lookup call. Why couldn't we have used the hostdev directly? Because the hostdev and mdev structures are incompatible. The way mdevs are currently removed is via a write to a specific sysfs attribute. If you do it while the machine which has the mdev assigned is running, the write call may block (with a new enough kernel, with older kernels it would return a write error!) until the device is no longer in use which is when the QEMU process exits. The interesting part here comes afterwards when we're cleaning up and call virHostdevReAttachMediatedDevices. The domain doesn't exist anymore, so the list of active hostdevs needs to be updated and the respective hostdevs removed from the list, but remember we had to create an mdev object in the memory in order to find it in the list first which will fail because the write to sysfs had already removed the mdev instance from the host system. And so the next time you try to start the same domain you'll get: "Requested operation is not valid: mediated device <path> is in use by driver QEMU, domain <name>" Fixes: https://gitlab.com/libvirt/libvirt/-/issues/119 Signed-off-by: Erik Skultety <eskultet@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>
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
* qemu/ - QEMU / KVM using qemu CLI/monitor
* remote/ - Generic libvirt native RPC client
* test/ - A "mock" driver for testing
* vbox/ - Virtual Box using native API
* vmware/ - VMware Workstation and Player using the vmrun tool
* xen/ - Xen using hypercalls, XenD SEXPR & XenStore
Finally some secondary drivers that are shared for several HVs.
Currently these are used by LXC, OpenVZ, QEMU and Xen drivers.
The ESX, Hyper-V, 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