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| author | Hanna Reitz <hreitz@redhat.com> | 2021-08-12 10:41:45 +0200 |
|---|---|---|
| committer | Hanna Reitz <hreitz@redhat.com> | 2021-09-15 15:54:07 +0200 |
| commit | 5a1cfd2150596bddbf429f81097cbd8b861515c0 (patch) | |
| tree | 6489c328deb19c4081f66cc89907bfd1dc5d9328 /include | |
| parent | 0bc329fbb009f8601cec23bf2bc48ead0c5a5fa2 (diff) | |
| download | qemu-5a1cfd2150596bddbf429f81097cbd8b861515c0.zip qemu-5a1cfd2150596bddbf429f81097cbd8b861515c0.tar.gz qemu-5a1cfd2150596bddbf429f81097cbd8b861515c0.tar.bz2 | |
block: Clarify that @bytes is no limit on *pnum
.bdrv_co_block_status() implementations are free to return a *pnum that
exceeds @bytes, because bdrv_co_block_status() in block/io.c will clamp
*pnum as necessary.
On the other hand, if drivers' implementations return values for *pnum
that are as large as possible, our recently introduced block-status
cache will become more effective.
So, make a note in block_int.h that @bytes is no upper limit for *pnum.
Suggested-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20210812084148.14458-4-hreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Diffstat (limited to 'include')
| -rw-r--r-- | include/block/block_int.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/include/block/block_int.h b/include/block/block_int.h index 437d746..5451f89 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -348,6 +348,15 @@ struct BlockDriver { * clamped to bdrv_getlength() and aligned to request_alignment, * as well as non-NULL pnum, map, and file; in turn, the driver * must return an error or set pnum to an aligned non-zero value. + * + * Note that @bytes is just a hint on how big of a region the + * caller wants to inspect. It is not a limit on *pnum. + * Implementations are free to return larger values of *pnum if + * doing so does not incur a performance penalty. + * + * block/io.c's bdrv_co_block_status() will utilize an unclamped + * *pnum value for the block-status cache on protocol nodes, prior + * to clamping *pnum for return to its caller. */ int coroutine_fn (*bdrv_co_block_status)(BlockDriverState *bs, bool want_zero, int64_t offset, int64_t bytes, int64_t *pnum, |