[libvirt-users] Which functions call qemu_driver API?

[Eric Blake]

On 08/14/2012 01:18 AM, He Xin wrote:
> Hi,
> 
>          Excuse me, I have watched qemu_driver.c where most of the libvirt
> API is overrided in order to connect qemu. But I am confused which functions
> then call those qemu_driver API? I mean where is the qemu_driver
> implementation? Libvirt.c? But how does the qemu_driver connect and control
> qemu?

src/libvirt.c contains the public API.  This API then calls a callback
from src/driver.h according to the URI.  If you connected to
test:///default, those callbacks live in src/test/test_driver.c.  If you
connected to qemu:///system or qemu:///session, then the first round of
those callbacks live in src/remote/remote_driver.c (to package the
request into an RPC call), which is then received by daemon/remote.c
(which unbundles the RPC call back into a public call to libvirt.c), and
then from the libvirtd process calls into src/qemu/qemu_driver.c.

Once you are in src/qemu/qemu_driver.c, most actions are either
persistent (altering state in the domain definition structure, using
functions from src/conf/domain_conf.c) or active (making monitor calls
over a UNIX socket to the running qemu process).  If you are asking how
monitor calls are made, then look into src/qemu/qemu_monitor.c which
then forwards to a text monitor (HMP - human monitor protocol, in qemu
<= 0.14, qemu_monitor_text.c) or the JSON monitor (QMP - qemu monitor
protocol using structured JSON queries, in qemu >= 0.15,
qemu_monitor_json.c).  There's also the task of initially starting up
the qemu process to have an attached monitor, see qemu_capabilities.c to
see how libvirt learns what qemu supports, and qemu_command.c to see how
libvirt constructs the command line arguments for starting qemu.

You seem to be asking a lot of questions, but not actually using gdb to
step through the whole process.  Try it - it's rather enlightening to
actually trace a call through the stack yourself, instead of asking
someone else to explain it all.  Note that you have to debug the
libvirtd process, rather than your application linked to libvirt.so,
thanks to the RPC boundary where your API calls are translated to an RPC
message to be passed between processes to reach libvirtd.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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