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Re: [Qemu-devel] barriers: block layer preparations


From: Jamie Lokier
Subject: Re: [Qemu-devel] barriers: block layer preparations
Date: Tue, 5 May 2009 23:49:04 +0100
User-agent: Mutt/1.5.13 (2006-08-11)

Christoph Hellwig wrote:
> > A barrier for read can be meaningful if the guest wishes to read a 
> > known-to-be-stable write.  I don't think any guest can make use of this 
> > though.
> 
> I don't know of any storage standard having anything like this or any
> OS taking advantage of it.  I'd be happy to review anything like that,
> though.

Several OSes have O_RSYNC, meaning reads hit the storage instead of
the OS cache.  I don't know if they bypass storage caches, but the
purpose seems to be to verify writes, and they will certainly bypass
storage caches if the OS or user turns off the storage caches.

-- Jamie




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