On Wed, Feb 01, 2017 at 01:13:39PM +0100, Max Reitz wrote: > On 30.01.2017 19:37, Eric Blake wrote: > > On 01/26/2017 07:27 AM, Daniel P. Berrange wrote: > >> On Thu, Jan 26, 2017 at 08:35:30PM +0800, Fam Zheng wrote: > >>> On Thu, 01/26 11:04, Daniel P. Berrange wrote: > >>>> The -n arg to the convert command allows use of a pre-existing image, > >>>> rather than creating a new image. This adds a -n arg to the dd command > >>>> to get feature parity. > >>> > >>> I remember there was a discussion about changing qemu-img dd's default to > >>> a > >>> "conv=nocreat" semantic, if so, "-n" might not be that useful. But that > >>> part > >>> hasn't made it into the tree, and I'm not sure which direction we should > >>> take. > >>> (Personally I think default to nocreat is a good idea). > >> > >> Use nocreat by default would be semantically different from real "dd" > >> binary which feels undesirable if the goal is to make "qemu-img dd" > >> be as consistent with "dd" as possible. > >> > >> It would be trivial to rewrite this patch to add support for the "conv" > >> option, allowing the user to explicitly give 'qemu-img dd conv=nocreat' > >> instead of my 'qemu-img dd -n' syntax, without changing default semantics. > > > > Adding 'conv=nocreat' (and not '-n') feels like the right way to me. > > The original idea was to make conv=nocreat a mandatory option, I think. > qemu-img was supposed error out if the user did not specify it.
I'm not really seeing a benefit in doing that - it would just break existing usage of qemu-img dd for no obvious benefit. FYI, I've implemented "conv" with "nocreat" and "notrunc" options which i'll post once i've tested some more. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
