On Fri, Jun 29, 2012 at 02:18:17PM +0800, Dennis Chen wrote:
On 06/28/2012 06:26 PM, Daniel P. Berrange wrote:
The '/dev/kvm' device is the low level kernel interface for creating virtual domains. This is not actually used by libvirt at all. The QEMU binary has code that talks to /dev/kvm, so all libvirt does is to spawn a QEMU process which in turns creates the virtual machine
All the libvirt code for this part is under $GIT/src/qemu/ in particular the qemu_command.c and qemu_process.c files
Daniel Thanks Daniel, now I understand that the libvirt code will play with QEMU binary, for example, qemu-system-x86_64, the latter will talk with KVM module . But now the question is, I guess qemuProcessStart() function was used to spawn a QEMU process, so I built a virsh from the source package with "-g -O0" flag, I want to gdb the virsh, but when I want to set a break point on qemuProcessStart(), I encounter issue:
#gdb virsh (gdb) b main Breakpoint 1 at 0x807d480: file virsh.c, line 20270. (gdb) r Starting program: /usr/bin/virsh [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/i386-linux-gnu/libthread_db.so.1".
Breakpoint 1, main (argc=1, argv=0xbffff294) at virsh.c:20270 20270 { (gdb) b qemuProcessStart Function "qemuProcessStart" not defined. Make breakpoint pending on future shared library load? (y or [n]) y Breakpoint 2 (qemuProcessStart) pending.
(gdb)c
virsh # create guest.xml Domain vdo created from vdo.xml
virsh #
continue instruction above doesn't hit the pending Breakpoint 2...
So my question is, which kind of object file will be created from $GIT/src/qemu folder during the build process, is it a .so file and virsh will load it?
virsh talks to the libvirtd daemon, the libvirtd daemon run those calls from the qemu driver. The documentation is relatively sparse, but reading what is available will help: http://libvirt.org/api.html http://libvirt.org/internals.html so if you want to step though that function you must gdb the libvirt daemon, not the client application. Daniel -- Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/ daniel@veillard.com | Rpmfind RPM search engine http://rpmfind.net/ http://veillard.com/ | virtualization library http://libvirt.org/