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Re: [Qemu-devel] [PATCH v3 1/2] block: sync bdrv_co_get_block_status_abo

From: Kevin Wolf
Subject: Re: [Qemu-devel] [PATCH v3 1/2] block: sync bdrv_co_get_block_status_above() with bdrv_is_allocated_above()
Date: Mon, 26 Sep 2016 17:04:21 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 19.09.2016 um 22:39 hat Eric Blake geschrieben:
> On 09/18/2016 11:37 PM, Denis V. Lunev wrote:
> > On 09/19/2016 04:21 AM, Fam Zheng wrote:
> >> On Thu, 09/15 19:34, Denis V. Lunev wrote:
> >>> They should work very similar, covering same areas if backing store is
> >>> shorter than the image. This change is necessary for the followup patch
> >>> switching to bdrv_get_block_status_above() in mirror to avoid assert
> >>> in check_block.
> >>>
> >>> This change should be made very carefully. Let us assume that we have
> >>> top image and 2 backing stores L0->L1->L2.
> >> Stupid question: which one is top and which are backing?
> > L0 is top, L2 is at bottom.
> I typically write this as:
> L2 <- L1 <- L0
> (read "L2 backs L1, which in turn backs L0") with the active on the
> right.  So I understand the confusion in Fam's question where you were
> using the opposite direction.

And I tend to use this one:

    base <- sn1 <- sn2 <- top

"sn*" isn't any better than "L*", but having at least one of "base" and
"top" (or "active") in there disambiguates the roles of the nodes.


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