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

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

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:

 * 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.

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