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Re: [PATCH v3 03/17] migration: Block migration comment or code is wrong

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH v3 03/17] migration: Block migration comment or code is wrong
Date: Tue, 8 Nov 2022 21:38:54 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2

On 11/8/22 21:36, Vladimir Sementsov-Ogievskiy wrote:
On 11/3/22 19:16, Avihai Horon wrote:
From: Juan Quintela <quintela@redhat.com>

And it appears that what is wrong is the code. During bulk stage we
need to make sure that some block is dirty, but no games with
max_size at all.

:) That made me interested in, why we need this one block, so I decided to 
search through the history.

And what I see? Haha, that was my commit 04636dc410b163c "migration/block: fix 
pending() return value" [1], which you actually revert with this patch.

So, at least we should note, that it's a revert of [1].

Still that this will reintroduce the bug fixed by [1].

As I understand the problem is (was) that in block_save_complete() we finalize 
only dirty blocks, but don't finalize the bulk phase if it's not finalized yet. 
So, we can fix block_save_complete() to finalize the bulk phase, instead of 
hacking with pending in [1].

Interesting, why we need this one block, described in the comment you refer to? 
Was it an incomplete workaround for the same problem, described in [1]? If so, 
we can fix block_save_complete() and remove this if() together with the comment 
from block_save_pending().

PS: Don't we want to deprecate block migration? Is it really used in 
production?  block-mirror is a recommended way to migrate block devices.

Best regards,

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