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Re: [Qemu-block] [PATCH v11 01/19] block: Add bdrv_drain_all_{begin, end

From: Alberto Garcia
Subject: Re: [Qemu-block] [PATCH v11 01/19] block: Add bdrv_drain_all_{begin, end}()
Date: Tue, 25 Oct 2016 16:48:25 +0200
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

On Tue 25 Oct 2016 04:38:27 PM CEST, Kevin Wolf wrote:

>> >>> My first thoughts were about how to let an unpause succeed without a
>> >>> previous pause for these objects, but actually I think this isn't
>> >>> what we should do. We rather want to actually do the pause instead
>> >>> because even new BDSes and block jobs should probably start in a
>> >>> quiesced state when created inside a drain_all section.
>> >>
>> >> Yes, I agree with this.  It shouldn't be too hard to implement it.  It
>> >> would require a BlockDriverState to look at the global "inside
>> >> bdrv_drain_all_begin" state, and ask its BlockBackend to disable
>> >> itself upon bdrv_replace_child.
>> > 
>> > Why in bdrv_replace_child()? bdrv_drain_all_end() enables all BDSs, but
>> > if you add one with "blockdev-add" it's not going to be disabled using
>> > this method.
>> You only need to disable it when blk_insert_bs is called.  In fact...
> This assumes that the block driver doesn't issue internal background I/O
> by itself. Probably true for everything that we have today, but it would
> probably be cleaner to quiesce it directly in bdrv_open_common().

And how about the rest of the things that are going on in



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