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Re: [Xen-devel] [PATCH]: Make Xen 3.1 IDE flush on O_DIRECT with drive caching off

  • To: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Chris Lalancette <clalance@xxxxxxxxxx>
  • Date: Wed, 27 Feb 2008 22:23:10 -0500
  • Delivery-date: Wed, 27 Feb 2008 19:23:39 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

Chris Lalancette wrote:
> All,
>      Long ago Xen added code to the device model to basically do an fsync()
> after every data write if the user in the guest specified that IDE write 
> caching
> should be disabled.  This works fine, except in the case where you are doing
> O_DIRECT writes inside the guest (ala dd if=/dev/zero of=/dev/hdb 
> oflag=direct).
>  This is because you can get out of ide_write_dma_cb() in the middle of the 
> loop
> without going through the logic to sync.  This simple patch makes sure that 
> you
> always check (and sync) inside the write callback.
> This patch applies to xen-3.1-testing.hg; I still have to test 3.2 (and the 
> new
> AIO code) to see if it is affected by this bug.

After some testing, it looks like 3.2 is not affected by this bug, so it
won't be needed there.

Chris Lalancette

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