On 06/29/2012 02:49 PM, Daniel Veillard wrote:
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
en, this Daniel is not that Daniel: ) I remember that I joined the
presentation about
libvirt delivered by you in Nanjing University last year.
Yes, the document about libvirt is sparse, so I am often confused when I
try to
understand the internals of the relationship between QEMU, KVM and
libvirt...
Let me go through the link you mentioned to see if I can understand
libvirtd comes from
and the relationship with libvirt...
BRs,
Dennis
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