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Date: Mon, 30 Nov 2015 17:09:49 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 01/15] block: Add "file" output
 parameter to block status query functions
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, Jeff Cody <jcody@redhat.com>, Peter Lieven <pl@kamp.de>, qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>

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