[PATCH v3 2/5] doc: Fix requirement on preferred size

[Eric Blake <eblake@redhat.com>]

Setting the preferred size to >= min(min_size, 4k) doesn't make
sense (a preferred size of 4k when min_size is 64k means that
you get efficient I/O when requesting something smaller than
the minimum granularity?).  Fix it by documenting the intended
semantics that the preferred size is >= max(min_size, 4k).

Reported-by: Vladimer Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 doc/proto.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/proto.md b/doc/proto.md
index adf2651..48a4ef5 100644
--- a/doc/proto.md
+++ b/doc/proto.md
@@ -776,7 +776,7 @@ client would be unable to access the final few bytes of the export.
 The preferred block size represents the minimum size at which aligned
 requests will have efficient I/O, avoiding behaviour such as
 read-modify-write.  If advertised, this MUST be a power of 2 at least
-as large as the smaller of the minimum block size and 2^12 (4,096),
+as large as the maximum of the minimum block size and 2^12 (4,096),
 although larger values (such as the minimum granularity of a hole) are
 also appropriate.  The preferred block size MAY be larger than the
 export size, in which case the client is unable to utilize the
-- 
2.14.3