Re: [libvirt] [Qemu-devel] KVM call minutes for Mar 15
* Anthony Liguori (anthony@codemonkey.ws) wrote:
On 03/15/2011 09:53 AM, Chris Wright wrote:
QAPI <snip> - c library implementation is critical to have unit tests and test driven development - thread safe? - no shared state, no statics. - threading model requires lock for the qmp session - licensiing? - LGPL - forwards/backwards compat? - designed with that in mind see wiki:
One neat feature of libqmp is that once libvirt has a better QMP passthrough interface, we can create a QmpSession that uses libvirt.
It would look something like:
QmpSession *libqmp_session_new_libvirt(virDomainPtr dom);
Looks like you mean this? -> request QmpSession -> client libvirt <- return QmpSession <- client -> QmpSession -> QMP -> QEMU So bypassing libvirt completely to actually use the session? Currently, it's more like: client -> QemuMonitorCommand -> libvirt -> QMP -> QEMU
The QmpSession returned by this call can then be used with all of the libqmp interfaces. This means we can still exercise our test suite with a guest launched through libvirt. It also should make the libvirt pass through interface a bit easier to consume by third parties.
This sounds like it's something libvirt folks should be involved with. At the very least, this mode is there now and considered basically unstable/experimental/developer use: "Qemu monitor command '%s' executed; libvirt results may be unpredictable!" So likely some concern about making it easier to use, esp. assuming that third parties above are mgmt apps, not just developers. thanks, -chris
On 03/15/2011 02:06 PM, Chris Wright wrote:
* Anthony Liguori (anthony@codemonkey.ws) wrote:
QAPI <snip> - c library implementation is critical to have unit tests and test driven development - thread safe? - no shared state, no statics. - threading model requires lock for the qmp session - licensiing? - LGPL - forwards/backwards compat? - designed with that in mind see wiki:
http://wiki.qemu.org/Features/QAPI One neat feature of libqmp is that once libvirt has a better QMP
On 03/15/2011 09:53 AM, Chris Wright wrote: passthrough interface, we can create a QmpSession that uses libvirt.
It would look something like:
QmpSession *libqmp_session_new_libvirt(virDomainPtr dom); Looks like you mean this?
-> request QmpSession -> client libvirt <- return QmpSession<-
client -> QmpSession -> QMP -> QEMU
Maybe, your ASCII art confuses me :-) QmpSession is just a wrapper around a transport. It can be an fd that you read() and write() JSON strings to, but it's just as easy to read and write through JSON strings via virQemuMonitorCommand() or whatever the interface currently is.
So bypassing libvirt completely to actually use the session?
Currently, it's more like:
client -> QemuMonitorCommand -> libvirt -> QMP -> QEMU
It's not bypassing. It's an API on top of a libvirt command. FWIW, the code generator could be trivially modified to generate a libvirt style API if there's any interest. So instead of: void qmp_block_passwd(QmpSession *sess, const char *device, const char *password, Error **errp); It would be: int virQemuBlockPasswd(virDomainPtr dom, const char *device, const char *password); But I'm not sure that's really that useful.
The QmpSession returned by this call can then be used with all of the libqmp interfaces. This means we can still exercise our test suite with a guest launched through libvirt. It also should make the libvirt pass through interface a bit easier to consume by third parties. This sounds like it's something libvirt folks should be involved with. At the very least, this mode is there now and considered basically unstable/experimental/developer use:
"Qemu monitor command '%s' executed; libvirt results may be unpredictable!"
So likely some concern about making it easier to use, esp. assuming that third parties above are mgmt apps, not just developers.
To be clear, there's no real support needed from libvirt here other than the passthrough. How that interface is supported in libvirt is more or less orthogonal to libqmp. libqmp is a C API to QMP. It can speak QMP over whatever transports speak QMP. If you can speak QMP to libvirt, then it's only natural to bridge libqmp to libvirt. Regards, Anthony Liguori
thanks, -chris
On Tue, Mar 15, 2011 at 12:06:06PM -0700, Chris Wright wrote:
* Anthony Liguori (anthony@codemonkey.ws) wrote:
On 03/15/2011 09:53 AM, Chris Wright wrote:
QAPI <snip> - c library implementation is critical to have unit tests and test driven development - thread safe? - no shared state, no statics. - threading model requires lock for the qmp session - licensiing? - LGPL - forwards/backwards compat? - designed with that in mind see wiki:
One neat feature of libqmp is that once libvirt has a better QMP passthrough interface, we can create a QmpSession that uses libvirt.
It would look something like:
QmpSession *libqmp_session_new_libvirt(virDomainPtr dom);
Looks like you mean this?
-> request QmpSession -> client libvirt <- return QmpSession <-
client -> QmpSession -> QMP -> QEMU
So bypassing libvirt completely to actually use the session?
Currently, it's more like:
client -> QemuMonitorCommand -> libvirt -> QMP -> QEMU
The QmpSession returned by this call can then be used with all of the libqmp interfaces. This means we can still exercise our test suite with a guest launched through libvirt. It also should make the libvirt pass through interface a bit easier to consume by third parties.
This sounds like it's something libvirt folks should be involved with. At the very least, this mode is there now and considered basically unstable/experimental/developer use:
"Qemu monitor command '%s' executed; libvirt results may be unpredictable!"
So likely some concern about making it easier to use, esp. assuming that third parties above are mgmt apps, not just developers.
Although we provide monitor and command line passthrough in libvirt, our recommendation is that mgmt apps do not develop against these APIs. Our goal / policy is that apps should be able todo anything they need using the formally modelled libvirt public APIs. The primary intended usage for the monitor/command line passthrough is debugging & experimentation, and as a very short term hack/workaround for mgmt apps while formal APIs are added to libvirt. In other words, we provide the feature because we don't want libvirt to be a roadblock, but we still strongly discourage their usage untill all other options have been exhausted. In same way as loading binary only modules into the kernels sets a 'tainted' flag, we plan that direct usage of monitor/command line passthrough will set a tainted flag against a VM. This is allow distro maintainers to identify usage & decide how they wish to support these features in products (if at all). Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
participants (3)
-
Anthony Liguori -
Chris Wright -
Daniel P. Berrange