block: Add qemu_{,try_}blockalign0()

These functions call their non-0-counterparts and then fill the
allocated buffer with 0 (if the allocation has been successful).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -5200,6 +5200,11 @@ void *qemu_blockalign(BlockDriverState *bs, size_t size)
     return qemu_memalign(bdrv_opt_mem_align(bs), size);
 }
 
+void *qemu_blockalign0(BlockDriverState *bs, size_t size)
+{
+    return memset(qemu_blockalign(bs, size), 0, size);
+}
+
 void *qemu_try_blockalign(BlockDriverState *bs, size_t size)
 {
     size_t align = bdrv_opt_mem_align(bs);
@@ -5213,6 +5218,17 @@ void *qemu_try_blockalign(BlockDriverState *bs, size_t size)
     return qemu_try_memalign(align, size);
 }
 
+void *qemu_try_blockalign0(BlockDriverState *bs, size_t size)
+{
+    void *mem = qemu_try_blockalign(bs, size);
+
+    if (mem) {
+        memset(mem, 0, size);
+    }
+
+    return mem;
+}
+
 /*
  * Check if all memory in this vector is sector aligned.
  */

include/block/block.h

@@ -412,7 +412,9 @@ void bdrv_img_create(const char *filename, const char *fmt,
 size_t bdrv_opt_mem_align(BlockDriverState *bs);
 void bdrv_set_guest_block_size(BlockDriverState *bs, int align);
 void *qemu_blockalign(BlockDriverState *bs, size_t size);
+void *qemu_blockalign0(BlockDriverState *bs, size_t size);
 void *qemu_try_blockalign(BlockDriverState *bs, size_t size);
+void *qemu_try_blockalign0(BlockDriverState *bs, size_t size);
 bool bdrv_qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov);
 
 struct HBitmapIter;