Re: [libvirt] how libvirt communicate with qemu?

On 10/21/2012 03:42 AM, yue wrote: Socket. Basically, libvirt pre-creates a Unix socket and hooks that up to the qemu -monitor command line argument, and then sends monitor commands over this socket when libvirt needs to tell qemu to do anything. src/qemu/qemu_agent.[ch] qemu is not a library - searching qemu-kvm source won't find you any of the functions used in libvirt. Rather, all libvirt<->qemu communication is done over sockets. src/libvirt.c has a list of all public libvirt API. src/driver.h has a callback structure for all driver implementations. src/qemu/qemu_driver.c installs qemuListAllDomains as the callback for the public function virConnectListAllDomains. conn is therefore the virConnectPtr you get when you open a connection to your specified URI (such as qemu:///system), and that conn pointer has enough information to point to the callback, so that virConnectListAllDomains then forwards into the qemuListAllDomains() function. You also need to understand the architecture of remote calls - remember, when virsh (or any other client) connects to qemu:///system, the local instance of virConnectListAllDomains() happens to call into the RPC driver rather than the qemu driver; that is, the local call is handled by src/remote/remote_driver.c which bundles the API call into an RPC packet. Then, in the libvirtd process, daemon/remote.c unbundles the RPC packet, and turns it back into an API call, but this time with the qemu driver instead of the RPC driver. So understanding the full path of a message requires debugging multiple processes. -- Eric Blake eblake(a)redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org