Re: [Qemu-devel] [RFC][PATCH v2] block: add write threshold reporting for block devices

[Francesco Romani <fromani@redhat.com>]

----- Original Message -----
> From: "Kevin Wolf" <kwolf@redhat.com>
> To: "Francesco Romani" <fromani@redhat.com>
> Cc: qemu-devel@nongnu.org, "Stefan Hajnoczi" <stefanha@gmail.com>, mdroth@linux.vnet.ibm.com, "Luiz Capitulino"
> <lcapitulino@redhat.com>, "Stefan Hajnoczi" <stefanha@redhat.com>
> Sent: Friday, November 21, 2014 11:11:26 AM
> Subject: Re: [Qemu-devel] [RFC][PATCH v2] block: add write threshold reporting for block devices
[...]
> > 1. I'm running a simple test using the attached script -
> > which is a qemu command line adapted from libvirt ouput driven
> > by oVirt. There is a way to attach a name at this stage, using a QMP
> > command?
> 
> No, node-name is assigned at the BlockDriverState (BDS) creation and
> can't be changed later on.

Makes sense to me.

> > 2. (related to the former) it seems from a not-so-deep look that the
> > blessed (only?)
> > way to set a proper node_name is using blockdev-add.
> > If so, I'm not sure I follow how the qemu boot flow would look like.
> > It will not be anymore as simple as crafting a command line and run the
> > qemu, right?
> > IIUC some interaction with QMP will be needed (sorry for asking silly
> > question,
> > trying to fill gaps in my knowledge).
> 
> -drive on the command line can do everything that blockdev-add can do.
> So let's assume you have a qcow2 image on a filesystem. Then you end up
> with two BDSes, one for the format driver and one for accessing the
> filesystem:
> 
>     BlockBackend (virtual device) -> qcow2 BDS -> file BDS (raw-posix.c)
> 
> For assigning a node name to the qcow2 BDS, you simply specify it in the
> obvious way:
> 
>     -drive file=test.qcow2,node-name=foo
> 
> Now if you want to assign a node name to the file BDS as well, you would
> get nested dicts in the blockdev-add call. In -drive a dot syntax is
> used to represent this:
> 
>     -drive file=test.qcow2,node-name=foo,file.node-name=bar
> 
> Are things a bit clearer with this?

Yes, thanks a lot. I was a bit misleaded by the lack of the reference (after a very quick
look) in the man page.
Maybe the manpage is out of date, but this is a different story -and maybe a different patch :)

New revision will come in a few days.

Bests,

-- 
Francesco Romani
RedHat Engineering Virtualization R & D
Phone: 8261328
IRC: fromani