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Re: [Qemu-devel] [PATCH 00/11] block: Use BB function in .bdrv_create()

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH 00/11] block: Use BB function in .bdrv_create() implementations
Date: Mon, 14 Mar 2016 18:34:31 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

Am 14.03.2016 um 17:55 hat Max Reitz geschrieben:
> On 14.03.2016 12:31, Kevin Wolf wrote:
> > Am 08.03.2016 um 17:34 hat Kevin Wolf geschrieben:
> >> All users of the block layers are supposed to go through a BlockBackend.
> >> The .bdrv_create() implementations are such users, so this series
> >> converts them.
> >>
> >> This series (specifically patch 1) will also help with moving the
> >> writethrough cache implementation from BDS to BB, where it really
> >> belongs. Once this is moved, it wouldn't be possible to use bdrv_open()
> >> to use a standalone BDS writethrough any more.
> >>
> >> Of course, writethrough doesn't make any sense in .bdrv_create() anyway,
> >> so while I'm still converting everything to BB where it would keep
> >> working (because that's the Right Thing), the drivers don't actually
> >> make use of this fact any more after this series.
> > 
> > Applied to the block branch.
> Now you can't name any BB "image" any more if you want to use e.g.
> drive-mirror. Intended?

Not really. :-/

Of course, you're supposed to use blockdev-mirror anyway (does it even
exist?), but we should avoid that. Fortunately, your "Further BB work"
will tie the name to a monitor reference and BBs without a name become
valid then, I think.

So this might be a good excuse for getting that series into 2.6. :-)


> Example:
> $ x86_64-softmmu/qemu-system-x86_64 -drive
> if=none,id=image,file=null-co://,driver=raw -qmp stdio
> {'execute':'qmp_capabilities'}
> {"return": {}}
> {'execute':'drive-mirror','arguments':{'device':'image','target':'foo.qcow2','sync':'full','format':'qcow2'}}
> Formatting 'foo.qcow2', fmt=qcow2 size=1073741824 encryption=off
> cluster_size=65536 lazy_refcounts=off refcount_bits=16
> {"error": {"class": "GenericError", "desc": "Device with id 'image'
> already exists"}}
> Max

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