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Re: [Qemu-block] [PATCH V2 3/5] virtio-blk: disable scsi passthrough by
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-block] [PATCH V2 3/5] virtio-blk: disable scsi passthrough by default |
Date: |
Wed, 15 Jul 2015 17:28:24 +0300 |
On Wed, Jul 15, 2015 at 04:18:49PM +0200, Paolo Bonzini wrote:
>
>
> On 15/07/2015 16:14, Michael S. Tsirkin wrote:
> > On Wed, Jul 15, 2015 at 02:47:24PM +0200, Paolo Bonzini wrote:
> >>
> >>
> >> On 15/07/2015 14:21, Michael S. Tsirkin wrote:
> >>>>> Disable scsi passthrough by default since it was incompatible with
> >>>>> virtio 1.0. For legacy machine types, keep this on by default.
> >>>>>
> >>>>> Cc: Stefan Hajnoczi <address@hidden>
> >>>>> Cc: Kevin Wolf <address@hidden>
> >>>>> Cc: address@hidden
> >>>>> Signed-off-by: Jason Wang <address@hidden>
> >>> Seems risky for 2.4. modern is off by default for now. Can't we limit
> >>> the change to when modern is enabled?
> >>
> >> That would have the effect of disabling a feature when you turn on modern.
> >
> > What's wrong with that?
>
> Weren't you complaining about it a few hours ago? :)
No, I complained about guest driver update disabling it.
> >>> I suggested changing this from bool to on/off/auto, and
> >>> make auto mean !modern.
> >>
> >> No, please do it like Jason did. The SCSI feature effectively had to be
> >> enabled explicitly already, the requests were marked as unsupported.
> >
> > I didn't know. How is it enabled?
>
> It's enabled by default in QEMU, but disabled by default in libvirt.
> And it only works if you pass a whole _disk_ (not a partition or logical
> volume) to QEMU, which is definitely not the common case.
>
> It can just be documented in the release notes; the feature is still
> available, and libvirt won't be broken because it adds explicitly both
> scsi=on and scsi=off.
>
> Paolo
So for libvirt, we don't really care about the default, right?
For command line, would it not be friendlier to make it follow the
modern flag automatically?