On 06/29/2012 12:25 AM, Dennis Chen wrote:
So my question is: how does the libvirt interaction with KVM to create a VM? Anybody can give me some tips about that, eg, the corresponding codes in libvirt?
http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/qemu/qemu_driver.c;h=2f93...
Yes, I noticed the code above in libvirt, but it's not related with my question in the first message...
Actually, yes it is. That's the code that libvirtd runs in reaction to your client code making an RPC code via libvirt.so.
I guess the qemuProcessStart() is used to spawn a QEMU process, but seems that lot's of tricks in its implementation, essentially, does this function spawn the qemu process looks like, eg:
StartProcess("/usr/bin/qemu-system-x86_64", ...);
Not StartProcess, so much as execve(), as wrapped in our virCommand API (src/util/command.c). If you want to see the exact command line that we constructed, look at /var/log/libvirt/qemu/$dom.log for the domain name that you are starting. It is a rather hairy command line; this is an example from one of my VMs: LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin QEMU_AUDIO_DRV=none /usr/bin/qemu-kvm -S -M pc-0.14 -cpu qemu32 -enable-kvm -m 768 -smp 1,sockets=1,cores=1,threads=1 -name fedora-local -uuid 24ab99db-bf50-085d-d3e5-7528243ae9b1 -nodefconfig -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/fedora-local.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive file=/var/lib/libvirt/images/fedora-local.img,if=none,id=drive-virtio-disk0,format=raw -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -drive file=/var/lib/libvirt/images/top.img,if=none,id=drive-virtio-disk1,format=qcow2 -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x3,drive=drive-virtio-disk1,id=virtio-disk1 -drive if=none,id=drive-ide0-1-0,readonly=on,format=raw -device ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0,bootindex=2 -netdev tap,fd=22,id=hostnet0,vhost=on,vhostfd=23 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:65:82:9e,bus=pci.0,addr=0x5 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -device usb-tablet,id=input0 -vnc 127.0.0.1:1 -k en-us -vga cirrus -device ES1370,id=sound0,bus=pci.0,addr=0x6 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x7 In turn, it is that hairy command line that starts the qemu process, and qemu then takes over the actual communication with the kernel via /dev/kvm to use KVM virtualization. -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org