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Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/so
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/something pre-christmas meeting |
Date: |
Wed, 20 Dec 2017 11:11:33 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Fri, Dec 15, 2017 at 05:38:00PM +0100, Max Reitz wrote:
> Image creation in qemu-system-* vs. qemu-img:
> In order to get proper introspection for qemu-img create, we need a
> QAPI schema. If we have a QAPI schema, we might as well add
> blockdev-create to QMP.
> As long as we do not have a really-none (null, void, ...) machine type
> for qemu-system-*, launching such a process just for creating an image
> will bring quite a bit of overhead (e.g. with -M none -accel qtest).
> However, as for libvirt, this is not exactly a regression since
> libvirt currently cannot create images at all (apart from implicitly
> through drive-mirror etc.). Further work on voidifying qemu-system-*
> will improve performance.
In terms of the I/O operations involved, image creation is a already a
pretty slow process, particularly if pre-allocation is used which is
common. So even QEMU's current slow (circa 300ms) startup time is a
complete non-issue for image creation IMHO - it'll be dwarfed by the
time to actually create the image.
> On the other side, we can also add QAPI introspection to qemu-img.
> (qemu-img already links to QAPI, so this should not be too hard.)
> qemu-img will also need command-line introspection, though.
I figure the qapi-ificiation is the hard & time consuming bit of
work. Once that's done exporting it via both qemu-img & qemu-system*
is quite straighforward.
> Plan B:
> libvirt can use qemu-img now with the currently supported options,
> and as soon as libvirt needs anything better, we will have something
> better done.
> (Also, there is "qemu-img create -f $format -o help"! Because
> parsing help texts has worked so well in the past.)
Regards,
Daniel
--
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- [Qemu-block] Raw notes from a small block layer/QAPI/something pre-christmas meeting, Max Reitz, 2017/12/15
- Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/something pre-christmas meeting, Markus Armbruster, 2017/12/18
- Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/something pre-christmas meeting, Kashyap Chamarthy, 2017/12/20
- Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/something pre-christmas meeting, Daniel P. Berrange, 2017/12/20
- Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/something pre-christmas meeting, Kashyap Chamarthy, 2017/12/20
- Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/something pre-christmas meeting, Kevin Wolf, 2017/12/20
- Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/something pre-christmas meeting, Daniel P. Berrange, 2017/12/20
- Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/something pre-christmas meeting, Peter Krempa, 2017/12/21
Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/something pre-christmas meeting,
Daniel P. Berrange <=
Re: [Qemu-block] [Qemu-devel] Raw notes from a small block layer/QAPI/something pre-christmas meeting, Vladimir Sementsov-Ogievskiy, 2017/12/22