block: New bdrv_set_buffer_alignment()

Device models should be able to set it without an unclean include of
block_int.h.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index febfd67..e986986 100644
--- a/block.c
+++ b/block.c
@@ -480,7 +480,6 @@
     bs->encrypted = 0;
     bs->valid_key = 0;
     bs->open_flags = flags;
-    /* buffer_alignment defaulted to 512, drivers can change this value */
     bs->buffer_alignment = 512;
 
     pstrcpy(bs->filename, sizeof(bs->filename), filename);
@@ -3115,7 +3114,10 @@
     return NULL;
 }
 
-
+void bdrv_set_buffer_alignment(BlockDriverState *bs, int align)
+{
+    bs->buffer_alignment = align;
+}
 
 void *qemu_blockalign(BlockDriverState *bs, size_t size)
 {