[PATCH v2 0/2] backup: allow specifying minimum cluster size

[Fiona Ebner <f.ebner@proxmox.com>]

Based-on: https://lore.kernel.org/qemu-devel/20240429115157.2260885-1-vsementsov@yandex-team.ru/

Discussion for v1:
https://lore.kernel.org/qemu-devel/20240308155158.830258-1-f.ebner@proxmox.com/

Changes in v2:
* Use 'size' type in QAPI.
* Remove option in cbw_parse_options(), i.e. before parsing generic
  blockdev options.
* Reword commit messages hoping to describe the issue in a more
  straight-forward way.

In the context of backup fleecing, discarding the source will not work
when the fleecing image has a larger granularity than the one used for
block-copy operations (can happen if the backup target has smaller
cluster size), because cbw_co_pdiscard_snapshot() will align down the
discard requests and thus effectively ignore then.

To make @discard-source work in such a scenario, allow specifying the
minimum cluster size used for block-copy operations and thus in
particular also the granularity for discard requests to the source.

Fiona Ebner (2):
  copy-before-write: allow specifying minimum cluster size
  backup: add minimum cluster size to performance options

 block/backup.c             |  2 +-
 block/block-copy.c         | 22 ++++++++++++++++++----
 block/copy-before-write.c  | 18 +++++++++++++++++-
 block/copy-before-write.h  |  1 +
 blockdev.c                 |  3 +++
 include/block/block-copy.h |  1 +
 qapi/block-core.json       | 17 ++++++++++++++---
 7 files changed, 55 insertions(+), 9 deletions(-)

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2.39.2