Re: [Xen-devel] Re: [patch] xen-blkback: sync I/O after backend disconnected

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Aug 15, 2011 at 10:46:10AM -0400, Christoph Hellwig wrote:
> On Mon, Aug 15, 2011 at 12:55:02PM +0800, Joe Jin wrote:
> > When backend disconnect, sync IO requests to the disk.
> 
> Care to explain why?

I was thinking it might be a good idea to do that when a disk
(file, LVM, real block device) is released from a guest just in case
there is some outstanding I/Os. But then I realized that we
bypasses the page cache anyhow - so there should be no outstanding I/O
requests - unless they are in the disk queue.

And the guest would normally issues a FLUSH when unmounting the
disk. Hm, I wonder what the conditions are when we forcibly kill the
guest - there might be outstanding I/Os in the disk's cache -
at which point we should probably sync the write cache, no?

> 
> Also you'll just need a sync_blockdev, fsync_bdev does far to many
> things that don't make any sense when you don't have a file system
> mounted on a device.
> 
> 
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