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Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set |
Date: |
Wed, 22 Jul 2015 18:42:07 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.0.1 |
On 22/07/2015 18:15, Michael S. Tsirkin wrote:
> > No, the feature is not desirable in the future. There is no reason
> > really not to use virtio-scsi passthrough instead, since virtio-scsi has
> > been out for about 3 years now and is stable.
>
> Given the amount of work we are spending handling this corner case,
> I'm beginning to think we should just bring it back in.
Please don't. Perhaps it made sense when Rusty was thinking of
virtio-blk as simply "struct request over virtio", but I'm not even sure
what the use case is.
For virtio-scsi, for example, one reason to use passthrough is that you
can use the same /dev/disk/by-id path on physical and virtual machines.
But that doesn't work with virtio-blk's pseudo passthrough.
Another is to pass "weird" devices (tapes, media changers, etc.) to
backup appliances, but that also doesn't work with virtio-blk.
So what is it used for? That's what is needed to make an informed decision.
> > In addition, the implementation would either not be compatible with
> > virtio 0.9, or would be different from everything else in the spec
> > because it requires a particular framing for the buffers.
>
> Of course we'll need some kind of change to avoid depending on framing
> of buffers, but how hard is it? Just stick the header size
> somewhere in the buffer or in the config space.
>
> Not compatible is probably not the right term to use here,
> since when using the legacy interface we can make the old
> framing assumption.
Not compatible in the sense that it requires work in the drivers too
(unlike e.g. CONFIG_WCE, where the old code just works with the proposed
modifications to 1.0).
Paolo
- Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set, (continued)
Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set, Daniel P. Berrange, 2015/07/22
- Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set, Jason Wang, 2015/07/22
- Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set, Michael S. Tsirkin, 2015/07/22
- Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set, Paolo Bonzini, 2015/07/22
- Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set, Daniel P. Berrange, 2015/07/22
- Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set, Paolo Bonzini, 2015/07/22
- Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set, Michael S. Tsirkin, 2015/07/22
Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set, Michael S. Tsirkin, 2015/07/22
Re: [Qemu-devel] [PATCH V3 2/3] virtio-blk: fail get_features when both scsi and 1.0 were set,
Paolo Bonzini <=
[Qemu-devel] [PATCH V3 3/3] virtio-blk: set VIRTIO_F_ANY_LAYOUT when 1.0 is supported, Jason Wang, 2015/07/22