From: Max Reitz <mreitz@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"qemu-block@nongnu.org" <qemu-block@nongnu.org>,
Denis Lunev <den@virtuozzo.com>
Subject: Re: [Qemu-devel] [PATCH 0/2] deal with BDRV_BLOCK_RAW
Date: Tue, 13 Aug 2019 17:04:18 +0200 [thread overview]
Message-ID: <cb79d424-09c9-0add-71d0-075f46a00da3@redhat.com> (raw)
In-Reply-To: <20190813150303.GK4663@localhost.localdomain>
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On 13.08.19 17:03, Kevin Wolf wrote:
> Am 13.08.2019 um 16:53 hat Max Reitz geschrieben:
>> On 13.08.19 16:46, Vladimir Sementsov-Ogievskiy wrote:
>>> 13.08.2019 17:31, Max Reitz wrote:
>>>> On 13.08.19 13:51, Kevin Wolf wrote:
>>>>
>>>> [...]
>>>>
>>>>> Hm... This is a mess. :-)
>>>>
>>>> Just out of curiosity: Why?
>>>>
>>>> Aren’t there only two things we really need from the block_status
>>>> infrastructure?
>>>>
>>>> (1) Whether something is allocated in the given layer of the backing chain,
>>>>
>>>> (2) Whether we know that a given range reads as zeroes.
>>>>
>>>> Do we really need anything else?
>>>>
>>>
>>> qemu-img map?
>>
>> Which is a debugging tool. So it doesn’t fall under “really” in my
>> book. If removing everything but allocation+zero information would make
>> the code a lot simpler, I think that would be worth it.
>>
>>> 1. We need to fix the bug somehow
>>> 2. We need to fix comment about different block-status flags, as it really
>>> lacks information of what actually "DATA" means (together with *file).
>>> And what finally means "allocated", can you define it precisely?
>>
>> As I wrote in my other mails, I think the problem is that it’s just
>> unexpected that block_status automatically skips through for filters.
>> It shouldn’t, that’s just black magic that the caller should not rely on.
>>
>> (We see precisely here that it’s wrong, because the callers are not
>> prepared for the allocation information returned to be associated with a
>> different node than what they passed.)
>>
>> So my definition is just “If the node has a COW backing file and
>> block_status returns ‘not allocated’, the data will be there.
>> Otherwise, the data is in the current node.” Yes, that means that
>> filters should appear as fully allocated.
>
> You can do that, but then the callers need to learn to do the recursion
> instead. After all, just copying everything if a filter is in the
> subtree isn't the desired behaviour.
Yes, hence the “deal with filters” series.
Max
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next prev parent reply other threads:[~2019-08-13 15:05 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-12 18:11 [Qemu-devel] [PATCH 0/2] deal with BDRV_BLOCK_RAW Vladimir Sementsov-Ogievskiy
2019-08-12 18:11 ` [Qemu-devel] [PATCH 1/2] block/raw-format: switch to BDRV_BLOCK_DATA with BDRV_BLOCK_RECURSE Vladimir Sementsov-Ogievskiy
2019-08-13 11:04 ` Kevin Wolf
2019-08-13 11:28 ` Vladimir Sementsov-Ogievskiy
2019-08-13 12:01 ` Kevin Wolf
2019-08-13 13:21 ` [Qemu-devel] [Qemu-block] " Kevin Wolf
2019-08-13 14:46 ` Max Reitz
2019-08-13 14:43 ` [Qemu-devel] " Max Reitz
2019-08-13 14:56 ` Vladimir Sementsov-Ogievskiy
2019-08-13 15:03 ` Max Reitz
2019-08-13 15:22 ` Vladimir Sementsov-Ogievskiy
2019-08-13 16:07 ` Max Reitz
2019-08-13 15:41 ` Kevin Wolf
2019-08-13 15:54 ` Vladimir Sementsov-Ogievskiy
2019-08-13 16:08 ` Kevin Wolf
2019-08-13 16:32 ` Vladimir Sementsov-Ogievskiy
2019-08-14 6:27 ` Vladimir Sementsov-Ogievskiy
2019-08-13 16:21 ` Max Reitz
2019-08-12 18:11 ` [Qemu-devel] [PATCH 2/2] iotests: test mirroring qcow2 under raw format Vladimir Sementsov-Ogievskiy
2019-08-13 9:10 ` Kevin Wolf
2019-08-13 9:22 ` Vladimir Sementsov-Ogievskiy
2019-08-13 9:36 ` Kevin Wolf
2019-08-12 19:46 ` [Qemu-devel] [PATCH 0/2] deal with BDRV_BLOCK_RAW Max Reitz
2019-08-12 19:50 ` Max Reitz
2019-08-13 8:39 ` Vladimir Sementsov-Ogievskiy
2019-08-13 9:01 ` Vladimir Sementsov-Ogievskiy
2019-08-13 9:33 ` Vladimir Sementsov-Ogievskiy
2019-08-13 11:14 ` Vladimir Sementsov-Ogievskiy
2019-08-13 11:51 ` Kevin Wolf
2019-08-13 13:00 ` Vladimir Sementsov-Ogievskiy
2019-08-13 14:31 ` Max Reitz
2019-08-13 14:46 ` Vladimir Sementsov-Ogievskiy
2019-08-13 14:53 ` Max Reitz
2019-08-13 15:03 ` Kevin Wolf
2019-08-13 15:04 ` Max Reitz [this message]
2019-08-13 14:50 ` Eric Blake
2019-08-13 9:34 ` Kevin Wolf
2019-08-13 14:38 ` Max Reitz
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