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Re: [Qemu-block] [PATCH v10 08/16] block: Support streaming to an interm

From: Alberto Garcia
Subject: Re: [Qemu-block] [PATCH v10 08/16] block: Support streaming to an intermediate layer
Date: Wed, 12 Oct 2016 16:33:43 +0200
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

On Wed 12 Oct 2016 04:23:05 PM CEST, Kevin Wolf <address@hidden> wrote:
>> +    /* Block all intermediate nodes between bs and base, because they
>> +     * will disappear from the chain after this operation */
>> +    for (iter = backing_bs(bs); iter && iter != base; iter = 
>> backing_bs(iter)) {
>> +        block_job_add_bdrv(&s->common, iter);
>> +    }
> In patch 6, you had a comment that the top node must be blocked as
> well because its backing file string will be updated. Isn't it the
> same for streaming?

In the block-stream case, 'device' is always the top node, and creating
the block job there already blocks all operations in it.

In the block-commit case, 'device' and 'top' are different parameters,
that's why 'top' must be explicitly blocked. I actually don't think that
we need to block 'device' at all, and we could even make the parameter
optional. That would be for a future patch, though. Also, the backing
file string is not updated in 'top', but in its overlay (unlike in
block-stream, 'top' disappears after a block-commit job).


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