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Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Int
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection |
Date: |
Wed, 15 May 2013 09:59:04 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 14.05.2013 um 18:45 hat Paolo Bonzini geschrieben:
> Il 14/05/2013 17:48, Wolfgang Richter ha scritto:
> > On Tue, May 14, 2013 at 6:04 AM, Paolo Bonzini <address@hidden
> > <mailto:address@hidden>> wrote:
> >
> > Il 14/05/2013 10:50, Kevin Wolf ha scritto:
> > > Or, to translate it into our existing terminology, drive-mirror
> > > implements a passive mirror, you're proposing an active one (which we
> > > do want to have).
> > >
> > > With an active mirror, we'll want to have another choice: The
> > mirror can
> > > be synchronous (guest writes only complete after the mirrored
> > write has
> > > completed) or asynchronous (completion is based only on the original
> > > image). It should be easy enough to support both once an active mirror
> > > exists.
> >
> > Right, I'm waiting for Stefan's block-backup to give me the "right"
> > hooks for the active mirror.
> >
> > The bulk phase will always be passive, but an active-asynchronous mirror
> > has some interesting properties and it makes sense to implement it.
> >
> >
> > Do you mean you'd model the 'active' mode after 'block-backup,' or actually
> > call functions provided by 'block-backup'?
>
> No, I'll just reuse the same hooks within block/mirror.c (almost... it
> looks like I need after_write too, not just before_write :( that's a
> pity).
Makes me wonder if using a real BlockDriver for the filter from the
beginning wouldn't be better than accumulating more and more hooks and
having to find ways to pass data from 'before' to 'after' hooks...
> Basically:
>
> 1) before the write, if there is space in the job's buffers, allocate a
> MirrorOp and a data buffer for the write. Also record whether the block
> was dirty before;
>
> 2) after the write, do nothing if there was no room to allocate the data
> buffer. Else clear the block from the dirty bitmap. If the block was
> dirty, read the whole cluster from the source as in passive mirroring.
> If it wasn't, copy the data from guest memory to the preallocated buffer
> and write it to the destination;
Does the "if there was no room" part mean that the mirror is active only
sometimes?
And why even bother with a dirty bitmap for an active mirror? The
background job that sequentially processes the whole image only needs a
counter, no bitmap.
At which point it looks like implementing it separate from mirror.c
could make more sense.
Kevin
- [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/13
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Stefan Hajnoczi, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/14
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection,
Kevin Wolf <=
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Kevin Wolf, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Paolo Bonzini, 2013/05/15
- Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/22
Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Wolfgang Richter, 2013/05/14
Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection, Richard W.M. Jones, 2013/05/16