lkml.org 
[lkml]   [2009]   [Aug]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] virtio-blk: set QUEUE_ORDERED_DRAIN by default
    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



    \
     
     \ /
      Last update: 2009-08-26 14:31    [W:0.023 / U:90.396 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site