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Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd |
Date: |
Mon, 15 May 2017 19:53:18 +0800 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Mon, 05/15 13:26, Peter Lieven wrote:
> Am 15.05.2017 um 12:50 schrieb Fam Zheng:
> > On Mon, 05/15 12:02, Peter Lieven wrote:
> > > Hi Block developers,
> > >
> > > I would like to add a feature to Qemu to drain all traffic from a block
> > > so that
> > > I can take external snaphosts without the risk to that in the middle of a
> > > write
> > > operation. Its meant for cases where where QGA freeze/thaw is not
> > > available.
> > >
> > > For me its enough to have this through qemu-io, but Kevin asked me to
> > > check
> > > if its not worth to have a stable API for it and present it via QMP/HMP.
> > >
> > > What are your thoughts?
> > For debugging purpose or a "hacky" usage where you know what you are doing,
> > it
> > may be fine to have this. The only issue is it should be a separate flag,
> > like
> > BlockJob.user_paused.
>
> How can I add, remove such a flag?
Like bs->user_drained. Set it in "drain" command, then increment
bs->quiesce_counter if toggled; vise versa.
>
> >
> > What happens from guest perspective? In the case of virtio, the request
> > queue is
> > not handled and -ETIMEDOUT may happen. With IDE, I/O commands are still
> > handled,
> > the command is not effective (or rather the implementation is not complete).
>
> That it only works with virtio is fine. However, the thing it does not work
> correctly
> apply then also to all other users of the drained_begin/end functions, right?
> As for the timeout I only plan to drain the device for about 1 second.
It didn't matter because for IDE, the invariant (staying quiesced as long as
necessary) is already ensured by BQL. Virtio is different because it supports
ioeventfd and data plane.
Fam
- [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Peter Lieven, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Fam Zheng, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Peter Lieven, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd,
Fam Zheng <=
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Peter Lieven, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Fam Zheng, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Peter Lieven, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Fam Zheng, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Peter Lieven, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Fam Zheng, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Peter Lieven, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Fam Zheng, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Kevin Wolf, 2017/05/15
- Re: [Qemu-devel] [RFC PATCH] qemu-io: add drain/undrain cmd, Peter Lieven, 2017/05/15