Re: [Libguestfs] [PATCH v8 2/4] v2v: add function qemu_img_version to utils

On Mon, Feb 06, 2017 at 11:06:46AM +0300, Roman Kagan wrote: > On Sat, Feb 04, 2017 at 03:10:44PM +0100, Tomáš Golembiovský wrote: > > The function returns version of qemu-img as a tuple (major, minor), or > > the value (0,9) in case there was an error detecting the version. > > Depending on QEMU version is extremly unreliable. Vendors often stick > with fairly old versions but backport important features (you at RedHat > know that, don't you ;) So it's not unlikely that e.g. a number of > future RHEV/RHEL releases won't use this new feature even though the > included QEMU already supports it. > > IMO a simpler and more reliable check is to construct a command line for > qemu-img that is lightweight to execute and succeeds if the option is > supported or fails otherwise. > > [ sorry for being so late with this ]

Yes, I agree. My quick testing shows that the following command should be sufficent to test for the "offset" parameter: $ truncate -s1024 /tmp/test2 $ qemu-img create /tmp/test -f qcow2 -b 'json:{"offset":512,"file":{"filename":"/tmp/test2"}}' On RHEL 7.3 it fails with: qemu-img: /tmp/test: Block format 'raw' used by device '' doesn't support the option 'offset' and return code 1. (Obviously we'd have to use real temporary files)

I'll see if I can make a patch ... Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org