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

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Message-ID: <20054.29964.556177.999449@mariner.uk.xensource.com>
Date:	Thu, 25 Aug 2011 17:15:08 +0100
From:	Ian Jackson <Ian.Jackson@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Christoph Hellwig <hch@...radead.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Jens Axboe <jaxboe@...ionio.com>,
	Greg Marsden <greg.marsden@...cle.com>,
	Joe Jin <joe.jin@...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

Konrad Rzeszutek Wilk writes ("Re: [Xen-devel] Re: [patch] xen-blkback: sync I/O after backend disconnected"):
> 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?

If we forcibly kill the guest we don't care about its IO in flight.
After all we are throwing away everything that the guest has in its
queue.

Bear in mind that the reason for forcibly killing (or perhaps forcibly
detaching) might be that the underlying device has wedged somehow.  It
would be annoying if that prevented even a force detach.

Or to put it in other words: force detach and force kill should be
lossy.  Their whole point is to be the lossy version.

Ian.
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