From: Paolo Bonzini <pbonzini@redhat.com>
To: Markus Armbruster <armbru@redhat.com>, Fam Zheng <famz@redhat.com>
Cc: kwolf@redhat.com,
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
"Denis V. Lunev" <den@virtuozzo.com>,
Stefan Hajnoczi <stefanha@gmail.com>,
qemu-devel@nongnu.org, jsnow@redhat.com
Subject: Re: [Qemu-devel] [PATCH v2 0/6] external backup api
Date: Fri, 26 Feb 2016 21:03:30 +0100 [thread overview]
Message-ID: <56D0AF92.7000509@redhat.com> (raw)
In-Reply-To: <56D0ADBD.20000@redhat.com>
On 26/02/2016 20:55, Paolo Bonzini wrote:
>
>
> On 19/02/2016 09:51, Markus Armbruster wrote:
>>> Is it an abuse to "Get LBA Status" to return dirty information? Because in SCSI
>>> the command reports "mapped", "allocated" and "anchored" statuses. Does that
>>> mean NBD will use a different status set?
>>
>> Perhaps some conceptual gymnastics can get us to standard semantics.
>>
>> Incremental backup wants to copy out an image's "dirty" blocks.
>>
>> We can view this as a bitmap telling us which of the image's blocks are
>> dirty.
>>
>> An alternative view would be base image + dirty delta image. In the the
>> dirty delta, exactly the dirty blocks are allocated. The delta image
>> may be conceptual.
>
> I see a problem here. On one hand I agree that the "GET LBA STATUS" is
> a natural extension to the NBD protocol.
>
> On the other hand, the Get LBA Status command in SCSI reflects the
> state over the whole chain, not only the top element. It is the
> equivalent of bdrv_get_block_status_above(bs, NULL, ...), rather than
> bdrv_get_block_status(bs, ...). My understanding is that the dirty
> block information would require the latter, especially in the
> "conceptual delta image" model that Markus describes above.
>
> Having NBD implement subtly different semantics compared to SCSI is a
> bad idea in my opinion.
>
> Of course if we call it "READ DIRTY BLOCKS" that would work, but I
> don't think such a command would be something that it makes sense to
> have in the general purpose NBD spec, so you would need a mechanism
> for vendor-specific extensions.
Trying to be constructive: shall we instead have a simple mini-protocol
with commands like "read bitmap slice", "clear bitmap slice", "query
next 0 bit", "query next 1 bit"?
Not necessarily QMP, just a little socket thing. It could be JSON or
ASCII or binary. It sucks to implement a new protocol, but perhaps it
could be something compatible with VMware or Parallels.
Sorry if this has already been proposed, I'm late to the game and I only
read this subthread.
Paolo
next prev parent reply other threads:[~2016-02-26 20:03 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-30 10:56 [Qemu-devel] [PATCH v2 0/6] external backup api Vladimir Sementsov-Ogievskiy
2016-01-30 10:56 ` [Qemu-devel] [PATCH 1/6] block dirty bitmap: add next_zero function Vladimir Sementsov-Ogievskiy
2016-01-30 10:56 ` [Qemu-devel] [PATCH 2/6] qmp: add query-block-dirty-bitmap-ranges Vladimir Sementsov-Ogievskiy
2016-02-10 10:08 ` Stefan Hajnoczi
2016-02-10 13:57 ` Denis V. Lunev
2016-02-10 15:26 ` John Snow
2016-02-10 15:36 ` Denis V. Lunev
2016-02-10 15:37 ` John Snow
2016-02-10 15:40 ` Denis V. Lunev
2016-02-14 5:05 ` Fam Zheng
2016-01-30 10:56 ` [Qemu-devel] [PATCH 3/6] iotests: test query-block-dirty-bitmap-ranges Vladimir Sementsov-Ogievskiy
2016-01-30 10:56 ` [Qemu-devel] [PATCH 4/6] qapi: add qmp commands for some dirty bitmap functions Vladimir Sementsov-Ogievskiy
2016-01-30 10:56 ` [Qemu-devel] [PATCH 5/6] qapi: make block-dirty-bitmap-create-successor transaction-able Vladimir Sementsov-Ogievskiy
2016-01-30 10:56 ` [Qemu-devel] [PATCH 6/6] iotests: test external backup api Vladimir Sementsov-Ogievskiy
2016-02-03 8:14 ` [Qemu-devel] [PATCH v2 0/6] " Fam Zheng
2016-02-03 10:57 ` Vladimir Sementsov-Ogievskiy
2016-02-03 11:02 ` Fam Zheng
2016-02-03 11:24 ` Vladimir Sementsov-Ogievskiy
2016-02-05 8:28 ` Denis V. Lunev
2016-02-05 8:44 ` Fam Zheng
2016-02-09 14:21 ` Stefan Hajnoczi
2016-02-09 14:37 ` Denis V. Lunev
2016-02-09 16:49 ` John Snow
2016-02-09 16:58 ` Denis V. Lunev
2016-02-09 18:12 ` John Snow
2016-02-09 19:25 ` Denis V. Lunev
2016-02-10 8:04 ` Denis V. Lunev
2016-02-09 14:28 ` Stefan Hajnoczi
2016-02-09 14:41 ` Denis V. Lunev
2016-02-10 10:10 ` Stefan Hajnoczi
2016-02-16 17:09 ` Stefan Hajnoczi
2016-02-16 17:17 ` Vladimir Sementsov-Ogievskiy
2016-02-16 17:20 ` Denis V. Lunev
2016-02-18 16:39 ` Stefan Hajnoczi
2016-02-18 17:07 ` Markus Armbruster
2016-02-17 17:47 ` Vladimir Sementsov-Ogievskiy
2016-02-18 0:59 ` Fam Zheng
2016-02-18 12:11 ` Daniel P. Berrange
2016-02-18 16:41 ` Stefan Hajnoczi
2016-02-19 2:08 ` Fam Zheng
2016-02-19 8:51 ` Markus Armbruster
2016-02-24 23:34 ` John Snow
2016-02-26 19:55 ` Paolo Bonzini
2016-02-26 20:03 ` Paolo Bonzini [this message]
2016-02-26 20:29 ` Denis V. Lunev
2016-02-26 21:37 ` John Snow
2016-02-26 20:40 ` Denis V. Lunev
2016-02-27 4:26 ` Fam Zheng
2016-02-29 8:14 ` Markus Armbruster
2016-02-29 8:54 ` Paolo Bonzini
2016-02-29 9:42 ` Paolo Bonzini
2016-02-29 10:05 ` Fam Zheng
2016-03-10 17:37 ` Stefan Hajnoczi
2016-03-10 17:40 ` Paolo Bonzini
2016-03-14 16:27 ` Denis V. Lunev
2016-02-29 10:22 ` Markus Armbruster
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=56D0AF92.7000509@redhat.com \
--to=pbonzini@redhat.com \
--cc=armbru@redhat.com \
--cc=den@virtuozzo.com \
--cc=famz@redhat.com \
--cc=jsnow@redhat.com \
--cc=kwolf@redhat.com \
--cc=qemu-devel@nongnu.org \
--cc=stefanha@gmail.com \
--cc=vsementsov@virtuozzo.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).