block: Switch transfer length bounds to byte-based

Sector-based limits are awkward to think about; in our on-going
quest to move to byte-based interfaces, convert max_transfer_length
and opt_transfer_length.  Rename them (dropping the _length suffix)
so that the compiler will help us catch the change in semantics
across any rebased code, and improve the documentation.  Use unsigned
values, so that we don't have to worry about negative values and
so that bit-twiddling is easier; however, we are still constrained
by 2^31 of signed int in most APIs.

When a value comes from an external source (iscsi and raw-posix),
sanitize the results to ensure that opt_transfer is a power of 2.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/block/block-backend.c b/block/block-backend.c
index 1fb070b4e4..e042544025 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1303,16 +1303,16 @@ int blk_get_flags(BlockBackend *blk)
     }
 }
 
-/* Returns the maximum transfer length, in sectors; guaranteed nonzero */
-int blk_get_max_transfer_length(BlockBackend *blk)
+/* Returns the maximum transfer length, in bytes; guaranteed nonzero */
+uint32_t blk_get_max_transfer(BlockBackend *blk)
 {
     BlockDriverState *bs = blk_bs(blk);
-    int max = 0;
+    uint32_t max = 0;
 
     if (bs) {
-        max = bs->bl.max_transfer_length;
+        max = bs->bl.max_transfer;
     }
-    return MIN_NON_ZERO(max, BDRV_REQUEST_MAX_SECTORS);
+    return MIN_NON_ZERO(max, INT_MAX);
 }
 
 int blk_get_max_iov(BlockBackend *blk)