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Date: Wed, 06 Mar 2013 19:31:51 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in
 .bdrv_truncate if we are shrinking
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To: Jeff Cody <jcody@redhat.com>
Cc: kwolf@redhat.com, sw@weilnetz.de, Peter Lieven <pl@dlhnet.de>, qemu-devel@nongnu.org, stefanha@redhat.com

Il 06/03/2013 19:14, Jeff Cody ha scritto:
> QCOW breaks with it using a normal raw posix file as a device.  As a
> test: qemu-img create -f qcow test.qcow 5G.  Now run qemu with that
> drive mounted, and try to partition and format it.  QEMU now asserts.
> 
> The nicety of being able to using truncate during a write call,
> especially for VHDX (which can have relatively large block/cluster
> sizes), so to grow the file sparsely in a dynamically allocated file.

Perhaps we need two APIs, "truncate" and "revalidate".

Truncate should be a no-op if (!bs->growable).

Revalidate could be called by the block_resize monitor command with no
size specified.

Paolo