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

[Paolo Bonzini <pbonzini@redhat.com>]

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(-)

-- 
1.8.2.1