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

[Paolo Bonzini <pbonzini@redhat.com>]

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.

v3->v4:
        new patch 6 to fix bdrv_co_is_allocated for removable media
        new patch 15 replacing custom code in qemu-img
        bdrv_is_allocated result checked everywhere
        make human-readable format really human-readable
        handle (actually ignore) errors in recursive get_block_status call

Paolo Bonzini (21):
  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: keep bs->total_sectors up to date even for growable block
    devices
  block: make bdrv_co_is_allocated static
  block: do not use ->total_sectors in bdrv_co_is_allocated
  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
  block: use bdrv_has_zero_init to return BDRV_BLOCK_ZERO
  block: return BDRV_BLOCK_ZERO past end of backing file
  qemu-img: add a "map" subcommand
  docs, qapi: document qemu-img map
  raw-posix: return get_block_status data and flags
  raw-posix: report unwritten extents as zero
  block: add default get_block_status implementation for protocols
  block: look for zero blocks in bs->file

 block.c                   | 174 +++++++++++++++++++--------------
 block/backup.c            |  4 ++--
 block/commit.c            |   6 +-
 block/cow.c               |  91 +++++++++++++-----
 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              |  23 ++++-
 block/vvfat.c             |  15 +--
 include/block/block.h     |  34 +++++--
 include/block/block_int.h |   2 +-
 qapi-schema.json          |  29 ++++++
 qemu-img-cmds.hx          |   6 ++
 qemu-img.c                | 238 +++++++++++++++++++++++++++++++++++++++++-----
 qemu-img.texi             |  55 +++++++++++
 qemu-io-cmds.c            |   4 +
 22 files changed, 643 insertions(+), 189 deletions(-)

-- 
1.8.3.1