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

[Alberto Garcia]

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).

Berto