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Re: [Qemu-block] [PATCH 00/17] block: transactionless incremental backup

From: John Snow
Subject: Re: [Qemu-block] [PATCH 00/17] block: transactionless incremental backup series
Date: Fri, 27 Feb 2015 19:38:14 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

On 02/27/2015 07:34 PM, Eric Blake wrote:
On 02/27/2015 04:47 PM, John Snow wrote:
New topic, new version, same great incremental backup taste.

This series relies on [Qemu-devel] [PULL 30/69] blkdebug: fix "once" rule,
part of Stefan's 69 patch pull request submitted 2015-02-27.

This patchset enables the in-memory part of the incremental backup
feature, without transactional support.

Support for transactions will come at a later date, but getting this
portion upstream will help stabilize work on bitmap persistence and
bitmap migration.

Transactional support is being postponed to allow more development
to create a transactional callback system that will allow objects used
by the drive backup routines to perform cleanup actions conditionally
based on the outcome of all backups in the transaction group.

Food for thought, and not necessarily fatal to this series:

What if this series makes 2.3, but transactions do not?  In the past,
we've had the benefit that if a standalone command exists, then the
matching transaction command also exists in the same release, such that
'query-commands' was a sufficient witness for what transactions we could
run.  But if we delay transactional incremental backup to 2.4, we'll
need some sort of introspection other than 'query-commands' to learn
what transaction elements are supported.

  - Removed Transactions, to be added later.
  - Removed Transaction tests, as above.

01: Indentation fixes.
     Removed enable/disable documentation.
     Added a note that transactions aren't implemented yet.
     Removed my needless commas
     Added error case documentation.

07: QMP enable/disable commands are deleted.

14: Some comments concerning assertions.
     Scrub re-alloc memory if we expand the array.
     Do not attempt to scrub memory if fix_count is 0

Changes made with Reviews kept:

02: Since 2.4

Oh, I didn't read far enough in my comments above.  If this entire
series is waiting for 2.4, then we stand a much better chance of getting
transaction support in the same release, negating all my worry above :)

Yeah, the feature is *so* weak without transactions that I don't really want to make the push without them.

I intend to send out the new transaction features ASAP, but I don't know if they'll get approved for 2.3 this late in the game. Heck, I can always just change the 'Since' text back.

04: Since 2.4
     Demingled the QMP command documentation.
08: Additions to what was qmp_block_dirty_enable/disable
     are no longer present as those function no longer exist.
09: Since 2.4
10: Since 2.4
     Demingled QMP command documentation.
11: Since 2.4
15: Test 112 --> 124
17: Number of tests altered. (Only 4, now.)

Fam Zheng (1):
   qapi: Add optional field "name" to block dirty bitmap

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