From 5a1cfd2150596bddbf429f81097cbd8b861515c0 Mon Sep 17 00:00:00 2001 From: Hanna Reitz Date: Thu, 12 Aug 2021 10:41:45 +0200 Subject: 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 Signed-off-by: Hanna Reitz Reviewed-by: Vladimir Sementsov-Ogievskiy Message-Id: <20210812084148.14458-4-hreitz@redhat.com> Reviewed-by: Eric Blake --- include/block/block_int.h | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'include/block') 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, -- cgit v1.1