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

[John Snow]

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.
>
> > Deletions:
> >   - Removed Transactions, to be added later.
> >   - Removed Transaction tests, as above.
> >
> > Changes:
> > 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