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block/io: introduce block driver snapshot-access API

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Add new block driver handlers and corresponding generic wrappers.
It will be used to allow copy-before-write filter to provide
reach fleecing interface in further commit.

In future this approach may be used to allow reading qcow2 internal
snapshots, for example to export them through NBD.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220303194349.2304213-11-vsementsov@virtuozzo.com>
[hreitz: Rebased on block GS/IO split]
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2022-03-03 20:43:43 +01:00 • committed by Hanna Reitz
parent 3b7ca26bdf
commit ce14f3b407
3 changed files with 99 additions and 0 deletions
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18
include/block/block_int-common.h
View file

@ -597,6 +597,24 @@ struct BlockDriver {
bool want_zero, int64_t offset, int64_t bytes, int64_t *pnum,
int64_t *map, BlockDriverState **file);
/*
* Snapshot-access API.
*
* Block-driver may provide snapshot-access API: special functions to access
* some internal "snapshot". The functions are similar with normal
* read/block_status/discard handler, but don't have any specific handling
* in generic block-layer: no serializing, no alignment, no tracked
* requests. So, block-driver that realizes these APIs is fully responsible
* for synchronization between snapshot-access API and normal IO requests.
*/
int coroutine_fn (*bdrv_co_preadv_snapshot)(BlockDriverState *bs,
int64_t offset, int64_t bytes, QEMUIOVector *qiov, size_t qiov_offset);
int coroutine_fn (*bdrv_co_snapshot_block_status)(BlockDriverState *bs,
bool want_zero, int64_t offset, int64_t bytes, int64_t *pnum,
int64_t *map, BlockDriverState **file);
int coroutine_fn (*bdrv_co_pdiscard_snapshot)(BlockDriverState *bs,
int64_t offset, int64_t bytes);
/*
* Invalidate any cached meta-data.
*/