On Thu, Jun 30, 2011 at 04:52:00PM +0200, Kevin Wolf wrote:
Am 30.06.2011 16:36, schrieb Marcelo Tosatti:
4. Live block copy API and high-level control - the main code that
adds the live block copy feature. Existing patches by Marcelo, can be
restructured to use common core by Marcelo.
Can use your proposed block_stream interface, with a "block_switch"
command on top, so:
1) management creates copy.img with backing file current.img, allows
access
2) management issues "block_switch dev copy.img"
3) management issues "block_stream dev base"
Isn't this block_switch command the same as the existing snapshot_blkdev?
Yep.
Thought of implementing "block_stream" command by reopening device with
blkstream:imagename.img
Then:
AIO_READ:
- for each cluster in request:
- if allocated-or-in-final-base, read.
- check write queue, if present wait on it, if not, add "copy"
entry to write queue.
- issue cluster sized read from source.
- on completion:
- copy data to original read buffer, complete it.
- if not cancelled, write cluster to destination.
AIO_WRITE
for each cluster in request:
- check write queue, cancel/wait for "copy" entry.
- add "guest" entry to write queue.
- issue write to destination.
- on completion:
- remove write queue entry.
With the 0...END background read, once it completes write final base
file for image.
So block_stream/block_stream_cancel/block_stream_status commands, the
background read and the rebase -u update can be separate from the block
driver.
The way how it works looks good to me, I'm just not entirely sure about
the right place to implement it. I think request queueing and copy on
read could be useful outside blkstream, too.
They could be lifted later, when there are other users.
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