On Thu, 07/04 23:10, Peter Lieven wrote: > > Am 04.07.2013 um 10:13 schrieb Paolo Bonzini <pbonz...@redhat.com>: > > > Il 03/07/2013 23:04, Peter Lieven ha scritto: > >>>> Define the return value of get_block_status. Bits 0, 1, 2 and 8-62 > >>>> are valid; bit 63 (the sign bit) is reserved for errors. Bits 3-7 > >>>> are left for future extensions. > >> Is Bit 8 not also reserved for future use? BDRV_SECTOR_BITS is 9. > > > > Right. > > > >> Can you explain which information is exactly returned in Bits 9-62? > > > > Bits 9-62 are the offset at which the data is stored in bs->file, they > > are valid if bit 2 (BDRV_BLOCK_OFFSET_VALID) is 1. > > Ok, so this is if bs->file is not linear? > > If we return the offset into bs->file this would only make sense if the data > at that position is raw and not encoded otherwise and if *pnum is limited > to the size of the extend at that position, right? Exactly. > > I currently do not understand for what operation this info is needed. Quoted from the cover letter: > 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.
Thanks. Fam
