[PATCH v2 3/6] block: Clarify that @bytes is no limit on *pnum

[Max Reitz <mreitz@redhat.com>]

.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: Max Reitz <mreitz@redhat.com>
---
 include/block/block_int.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index fcb599dd1c..f85b96ed99 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -347,6 +347,11 @@ 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.
      */
     int coroutine_fn (*bdrv_co_block_status)(BlockDriverState *bs,
         bool want_zero, int64_t offset, int64_t bytes, int64_t *pnum,
-- 
2.31.1