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Date: Thu, 7 May 2015 15:20:56 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v2 0/3] block: Warn about
 usage of growing formats over non-growable protocols
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, qemu-block@nongnu.org, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Max Reitz <mreitz@redhat.com>

Am 07.05.2015 um 14:47 hat Paolo Bonzini geschrieben:
> 
> 
> On 07/05/2015 14:29, Kevin Wolf wrote:
> > > No, it shouldn't indeed.
> > > 
> > > Could alloc_clusters_noref do bdrv_truncate and return ENOSPC if it
> > > fails?  That's how for example qcow and vhdx work.  vdi has the same
> > > problem.
> > 
> > If you want NBD to return -ENOSPC for writes after EOF, change the
> > nbd block driver to do just that. There's no reason to add additional
> > overhead to qcow2 (even over raw-posix) for that.
> 
> Does ENOSPC over LVM (dm-linear) work at all, and who generates the
> ENOSPC there?

The LVM use case is what oVirt uses, so I'm pretty sure that it works.
I'm now sure who generates the ENOSPC, but it's not qemu anyway. If I
had to guess, I'd say that the kernel block layer might just forbid
writing after EOF for any block device.

Kevin