BlockLimits: introduce max_transfer_length

Signed-off-by: NPeter Lieven <pl@kamp.de>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block.c

@@ -519,6 +519,7 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
             return;
         }
         bs->bl.opt_transfer_length = bs->file->bl.opt_transfer_length;
+        bs->bl.max_transfer_length = bs->file->bl.max_transfer_length;
         bs->bl.opt_mem_alignment = bs->file->bl.opt_mem_alignment;
     } else {
         bs->bl.opt_mem_alignment = 512;
@@ -533,6 +534,9 @@ void bdrv_refresh_limits(BlockDriverState *bs, Error **errp)
         bs->bl.opt_transfer_length =
             MAX(bs->bl.opt_transfer_length,
                 bs->backing_hd->bl.opt_transfer_length);
+        bs->bl.max_transfer_length =
+            MIN_NON_ZERO(bs->bl.max_transfer_length,
+                         bs->backing_hd->bl.max_transfer_length);
         bs->bl.opt_mem_alignment =
             MAX(bs->bl.opt_mem_alignment,
                 bs->backing_hd->bl.opt_mem_alignment);

include/block/block_int.h

@@ -289,6 +289,9 @@ typedef struct BlockLimits {
     /* optimal transfer length in sectors */
     int opt_transfer_length;
 
+    /* maximal transfer length in sectors */
+    int max_transfer_length;
+
     /* memory alignment so that no bounce buffer is needed */
     size_t opt_mem_alignment;
 } BlockLimits;