block-backend: align max_transfer to request alignment

Git-commit: b99f7fa08a3df8b8a6a907642e5851cdcf43fa9f
References: bsc#1190425

Block device requests must be aligned to bs->bl.request_alignment.
It makes sense for drivers to align bs->bl.max_transfer the same
way; however when there is no specified limit, blk_get_max_transfer
just returns INT_MAX.  Since the contract of the function does not
specify that INT_MAX means "no maximum", just align the outcome
of the function (whether INT_MAX or bs->bl.max_transfer) before
returning it.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Lin Ma <lma@suse.com>

diff --git a/block/block-backend.c b/block/block-backend.c
index 8b8f2a80a0d52635059e0315ae169623818a40e7..5344126d1ec81a0af792758da1ad125c4b55ed04 100644 (file)
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1829,12 +1829,12 @@ uint32_t blk_get_request_alignment(BlockBackend *blk)
 uint32_t blk_get_max_transfer(BlockBackend *blk)
 {
     BlockDriverState *bs = blk_bs(blk);
-    uint32_t max = 0;
+    uint32_t max = INT_MAX;
 
     if (bs) {
-        max = bs->bl.max_transfer;
+        max = MIN_NON_ZERO(max, bs->bl.max_transfer);
     }
-    return MIN_NON_ZERO(max, INT_MAX);
+    return ROUND_DOWN(max, blk_get_request_alignment(blk));
 }
 
 int blk_get_max_iov(BlockBackend *blk)