Re: [Qemu-devel] RFC: raw device support for block device targets

[Alex Bligh]

--On 8 December 2011 13:40:57 +0100 Kevin Wolf <address@hidden> wrote:

> > qemu-img convert appears to support block devices as input, but not
> > as output. That is irritating, as when using qemu-img convert to
> > convert qcow to raw on a block partition, an intermediate file has
> > to be used, which slows things down and pointlessly uses disk space.
> >
> > The problem is that ftruncate() is being called on the output file
> > in order ensure it is sufficiently large, and this fails on
> > block devices.
...
> Creating an image on a block device shouldn't even call raw_create(),
> but only hdev_create(), which doesn't try to truncate the device, but
> just uses lseek to make sure that it's large enough.
>
> Which qemu version are you using and what's your command line?

I was testing on:

address@hidden:~$ qemu-img --version
qemu-img version 0.12.3, Copyright (c) 2004-2008 Fabrice Bellard

though the patch was against current trunk.

Command line simply:

qemu-img convert -O raw test.qcow /dev/xyz

Fails on ftruncate() as verified with strace.

I must admit I only 'tested' on trunk by reading the source.

--
Alex Bligh