Re: [Qemu-devel] [PATCH v3 01/15] block: Add "file" output parameter to block status query functions

[Fam Zheng]

On Mon, 11/30 16:38, Stefan Hajnoczi wrote:
> On Thu, Nov 26, 2015 at 01:05:21PM +0800, Fam Zheng wrote:
> > @@ -1535,13 +1541,14 @@ static int64_t coroutine_fn 
> > bdrv_co_get_block_status(BlockDriverState *bs,
> >          }
> >      }
> >  
> > -    if (bs->file &&
> > +    if (*file && *file != bs &&
> >          (ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO) &&
> >          (ret & BDRV_BLOCK_OFFSET_VALID)) {
> 
> What is the purpose of this change?

The code here is to sensibly detect "zero" by going into the "file" which the
offset is valid for. Now the "file" is no longer always "bs->file", so we use
the returned "file" pointer instead.

Fam