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Re: [Qemu-devel] [RFC PATCH 07/17] block: make high level discard operat
From: |
Avi Kivity |
Subject: |
Re: [Qemu-devel] [RFC PATCH 07/17] block: make high level discard operation always zero |
Date: |
Mon, 12 Mar 2012 14:03:45 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120216 Thunderbird/10.0.1 |
On 03/12/2012 01:04 PM, Kevin Wolf wrote:
> >>
> >> qcow2 can't handle clusters that are referenced twice from the same L1
> >> table. This would require a reverse lookup to adjust the QCOW_O_COPIED
> >> flags in the L2 tables containing the other references.
> >
> > Don't follow, sorry. What adjustment are you talking about?
> >
> > If it's a 1->0 transition, is it mandatory to adjust the flag? That is,
> > it it legal to have a refcount of exactly one, but have the flag clear?
>
> According to the spec it's illegal and qemu-img check will complain,
> too. In practice, I'm not entirely sure if it will cause real corruption
> or just unnecessary COWs. I believe it may be the latter.
We could retro-doc it but I'm not a huge fan of this practice.
> But it's not worth the trouble anyway when we can have a real zero flag
> in qcow3.
ok. Thanks for the explanations.
--
error compiling committee.c: too many arguments to function
- [Qemu-devel] [RFC PATCH 12/17] ide/scsi: turn on discard, (continued)
- [Qemu-devel] [RFC PATCH 12/17] ide/scsi: turn on discard, Paolo Bonzini, 2012/03/08
- [Qemu-devel] [RFC PATCH 01/17] qemu-iotests: add a simple test for write_zeroes, Paolo Bonzini, 2012/03/08
- [Qemu-devel] [RFC PATCH 11/17] ide/scsi: prepare for flipping the discard defaults, Paolo Bonzini, 2012/03/08
- [Qemu-devel] [RFC PATCH 16/17] qemu-io: fix the alloc command, Paolo Bonzini, 2012/03/08
- [Qemu-devel] [RFC PATCH 07/17] block: make high level discard operation always zero, Paolo Bonzini, 2012/03/08
[Qemu-devel] [RFC PATCH 08/17] block: kill the write zeroes operation, Paolo Bonzini, 2012/03/08
[Qemu-devel] [RFC PATCH 15/17] raw: add get_info, Paolo Bonzini, 2012/03/08
[Qemu-devel] [RFC PATCH 14/17] block: support FALLOC_FL_PUNCH_HOLE trimming, Paolo Bonzini, 2012/03/08
Re: [Qemu-devel] [RFC PATCH 14/17] block: support FALLOC_FL_PUNCH_HOLE trimming, Stefan Hajnoczi, 2012/03/09