Re: [Qemu-devel] [PATCH v4 00/21] Add qemu-img subcommand to dump file metadata

[Stefan Hajnoczi]

On Thu, Aug 29, 2013 at 04:00:00PM +0200, Paolo Bonzini wrote:
> This series adds a subcommand to "qemu-img" 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
> 
> 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.
> 
> The patches implement a new operation, bdrv_co_get_block_status, that
> supersedes bdrv_co_is_allocated.  The bdrv_is_allocated API is still
> available of course, and implemented on top of the new operation.
> 
> Patches 1-3 touch cow, which uses bdrv_co_is_allocated during its reads
> and writes.  I optimized it a bit because it was unbearably slow during
> testing.  With these patches (also tested with blkverify), booting of
> a cow guest image is not particularly slow.
> 
> Patch 4 fixes the bs->total_sectors file size cache, which is used in
> bdrv_co_get_block_status to clamp invalid input.
> 
> Patches 5 to 8 clean up the bdrv_is_allocated and bdrv_is_allocated_above
> implementation, eliminating some code duplication.
> 
> Patches 9 and 10 tweak bdrv_has_zero_init and its usage in qemu-img in
> a way that helps when implementing the new API.
> 
> Patches 11 to 15 implement bdrv_get_block_status and change the formats
> to report all the available information.
> 
> Patch 16 and 17 adds the "map" subcommand to qemu-img, and the relevant
> documentation.
> 
> Finally, patches 18 to 21 tweak the implementation to extract more
> information from protocols, and combine this information with format
> metadata whenever possible.

Please rebase on qemu.git/master (includes raw BSD and other potential
conflicts).

Stefan