On Mon, Sep 01, 2014 at 07:55:22AM -0000, senya wrote: > I'm trying to reanimate github.com/jagane/qemu-kvm-livebackup > there is a separate thread which connects with client through socket and > sends disk blocks to it.
Regarding your original question about threads: it is possible to do block I/O from threads but there are rules about how to do that safely. The natural way to do things in QEMU is not with threads, this was always an issue with Jagane's patches (I guess he didn't want to spend time integrating it into QEMU's main loop when prototyping the code but it's not a good long-term solution). More about livebackup: There has been more recent work by Fam Zheng to achieve the same thing. The advantage of Fam's approach is that it reuses existing QEMU primitives instead of adding special case livebackup code. Fam has moved on to other work but his latest patches are from May so picking them up again shouldn't be that hard. It consists of two things: image fleecing and dirty bitmap commands. Image fleecing gives cheap access to a point-in-time snapshot of the disk (over NBD). Internally it uses the run-time NBD server and the block-backup command to export a point-in-time snapshot. The dirty bitmap provides what Jagane did but the plan is to also persist bitmaps across QEMU shutdown. This will make incremental backups easy. Please see Part IV of the "Block layer status report" presentation for an overview: http://www.linux-kvm.org/wiki/images/4/41/Kvm-forum-2013-block-layer-status-report.pdf Here are Fam's patch series: https://lists.gnu.org/archive/html/qemu-devel/2014-05/msg03880.html https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg05250.html The first step is getting the image fleecing code merged. Then the in-memory dirty bitmap can be merged. Finally, persistent dirty bitmap support can be written. Stefan
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