Re: [PATCH v2] introduce a cache options for PV disks

[Ian Campbell <Ian.Campbell@citrix.com>]

On Thu, 2013-06-27 at 17:50 +0100, Ian Jackson wrote:
> Ian Campbell writes ("Re: [PATCH v2] introduce a cache options for PV disks"):
> > I think I can parse it now. It doesn't really say what the option does
> > though. I'd expect it to say something about "disabling the workaround"
> > or "the backend may use O_DIRECT".
> 
> How about:

Sounds good thanks.

> 
>  * direct-io-safe
>  *      Values:         0/1 (boolean)
>  *      Default Value:  0
>  *
>  *      The underlying storage is not affected by the direct IO memory
>  *      lifetime bug.  See:
>  *        http://lists.xen.org/archives/html/xen-devel/2012-12/msg01154.html
>  *
>  *      Therefore this option gives the backend permission to use
>  *      O_DIRECT, notwithstanding that bug.
>  *
>  *      That is, if this option is enabled, use of O_DIRECT is safe,
>  *      in circumstances where we would normally have avoided it as a
>  *      workaround for that bug.  This option is not relevant for all
>  *      backends, and even not necessarily supported for those for
>  *      which it is relevant.  A backend which knows that it is not
>  *      affected by the bug can ignore this option.
>  *
>  *      This option doesn't require a backend to use O_DIRECT, so it
>  *      should not be used to try to control the caching behaviour.
> 
> Ian.