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

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Message-ID: <20110815151042.GA22541@dumpdata.com>
Date:	Mon, 15 Aug 2011 11:10:42 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Joe Jin <joe.jin@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Jens Axboe <jaxboe@...ionio.com>,
	Greg Marsden <greg.marsden@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ian Campbell <Ian.Campbell@...citrix.com>,
	Kurt C Hackel <KURT.HACKEL@...cle.com>
Subject: Re: [Xen-devel] Re: [patch] xen-blkback: sync I/O after backend
 disconnected

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.
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xensource.com
> http://lists.xensource.com/xen-devel
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