Re: [Qemu-devel] [PATCH 00/17] Add qemu-img subcommand to dump file metadata

[Stefan Hajnoczi]

On Wed, Jul 03, 2013 at 04:34:14PM +0200, 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
> 
> 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.
> 
> Patches 4 to 6 clean up the bdrv_is_allocated and bdrv_is_allocated_above
> implementation, eliminating some code duplication.
> 
> Patches 7 and 8 tweak bdrv_has_zero_init and its usage in qemu-img in
> a way that helps when implementing the new API.
> 
> Patches 9 to 11 implement bdrv_get_block_status and change the formats
> to report all the available information.
> 
> Patch 12 adds the "map" subcommand to qemu-img.
> 
> Finally, patches 13 to 17 tweak the implementation to extract more
> information from protocols, and combine this information with format
> metadata whenever possible.
> 
> Paolo
> 
> Paolo Bonzini (17):
>   cow: make reads go at a decent speed
>   cow: make writes go at a less indecent speed
>   cow: do not call bdrv_co_is_allocated
>   block: make bdrv_co_is_allocated static
>   block: remove bdrv_is_allocated_above/bdrv_co_is_allocated_above
>     distinction
>   block: expect errors from bdrv_co_is_allocated
>   qemu-img: always probe the input image for allocated sectors
>   block: make bdrv_has_zero_init return false for copy-on-write-images
>   block: introduce bdrv_get_block_status API
>   block: define get_block_status return value
>   block: return get_block_status data and flags for formats
>   qemu-img: add a "map" subcommand
>   block: use bdrv_has_zero_init to return BDRV_BLOCK_ZERO
>   raw-posix: return get_block_status data and flags
>   raw-posix: detect XFS unwritten extents
>   block: add default get_block_status implementation for protocols
>   block: look for zero blocks in bs->file
> 
>  block.c                   | 134 +++++++++++++--------------
>  block/commit.c            |   6 +-
>  block/cow.c               |  90 +++++++++++++------
>  block/mirror.c            |   4 +-
>  block/qcow.c              |  13 ++-
>  block/qcow2.c             |  24 +++--
>  block/qed.c               |  39 ++++++--
>  block/raw-posix.c         |  24 +++--
>  block/raw.c               |   6 +-
>  block/sheepdog.c          |  14 +--
>  block/stream.c            |  10 +--
>  block/vdi.c               |  17 +++-
>  block/vmdk.c              |  20 ++++-
>  block/vvfat.c             |  15 ++--
>  include/block/block.h     |  31 +++++--
>  include/block/block_int.h |   2 +-
>  qemu-img-cmds.hx          |   6 ++
>  qemu-img.c                | 225 
> +++++++++++++++++++++++++++++++++++++++++-----
>  18 files changed, 497 insertions(+), 183 deletions(-)

Makes sense to me.  I have left a few small comments but nothing major.

Stefan