On 07/16/2013 10:29 AM, Paolo Bonzini wrote: > This series adds a subcommand to "map" that can dump file metadata. > Metadata that is dumped includes: > > - whether blocks are allocated in bs->file and, if so, where > > - whether blocks are zero > > - whether data is read from bs or bs->backing_hd
Is this command only usable from qemu-img, or is there a QMP counterpart for getting at the same information on a live image while qemu is running? > > Metadata is dumped for an entire chain of images. One example usage is > (for non-compressed, non-encrypted images) to transform the metadata > into a Linux device-mapper setup, and make a qcow2 image available (for > read only) as a block device. Another possible usage is to determine > the used areas of a file, and convert it in place to another format. > Alternatively, the richer data can be used by block jobs to quickly > determine if a block is zero without reading it. Definitely useful information! I haven't looked at the implementation yet, but there had better be a JSON representation of the output :) -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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