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Re: [Qemu-devel] [PATCH v2 0/3] block: Warn about usage of growing forma

From: Max Reitz
Subject: Re: [Qemu-devel] [PATCH v2 0/3] block: Warn about usage of growing formats over non-growable protocols
Date: Wed, 06 May 2015 15:04:32 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 05.05.2015 11:46, Stefan Hajnoczi wrote:
On Thu, Mar 19, 2015 at 03:03:18PM -0400, Max Reitz wrote:
Some image formats (e.g. qcow2) require the underlying file to grow on
write accesses, but this is in fact not supported by all protocols (e.g.
nbd does not). If such a format requiring file growth is used
non-read-only over a protocol which does not support this, a warning
should be issued.

This warning is issued for example whenever one tries to export a qcow2
image over nbd-server and use the export from qemu.
The warning implies that the user should switch to read-only or a
different protocol, but this configuration is perfectly normal.  For
example, oVirt uses qcow2 on LVM volumes.

Introducing a warning for a normal QEMU invocation is a bit weird.

What is the point of this series?  Were users confused that they hit

Users were confused when exporting a qcow2 image using nbd-server instead of qemu-img, and then accessing that NBD export with qemu (subsequently getting I/O errors on guest writes, if the image is not yet fully allocated): http://bugzilla.redhat.com/show_bug.cgi?id=1090713


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