Messages in this thread | | | Date | Wed, 26 Aug 2009 15:28:13 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH] virtio-blk: set QUEUE_ORDERED_DRAIN by default |
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On 08/26/2009 03:06 PM, Rusty Russell wrote: > On Tue, 25 Aug 2009 11:46:08 pm Christoph Hellwig wrote: > >> On Tue, Aug 25, 2009 at 11:41:37PM +0930, Rusty Russell wrote: >> >>> On Fri, 21 Aug 2009 06:26:16 am Christoph Hellwig wrote: >>> >>>> Currently virtio-blk doesn't set any QUEUE_ORDERED_ flag by default, which >>>> means it does not allow filesystems to use barriers. But the typical use >>>> case for virtio-blk is to use a backed that uses synchronous I/O >>>> >>> Really? Does qemu open with O_SYNC? >>> >>> I'm definitely no block expert, but this seems strange... >>> Rusty. >>> >> Qemu can open it various ways, but the only one that is fully safe >> is O_SYNC (cache=writethrough). >> > (Rusty goes away and reads the qemu man page). > > By default, if no explicit caching is specified for a qcow2 disk image, > cache=writeback will be used. >
It's now switched to writethrough. In any case, cache=writeback means "lie to the guest, we don't care about integrity".
> Are you claiming qcow2 is unusual? I can believe snapshot is less common, > though I use it all the time. > > You'd normally have to add a feature for something like this. I don't > think this is different. >
Why do we need to add a feature for this?
-- error compiling committee.c: too many arguments to function
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