Re: [Scst-devel] [Xen-devel] iSCSI connection corrupts Xen block devices.

[Dr. G. W. <gr...@wi...>]

On Mar 26, 10:14am, =?ISO-8859-1?Q?Roger_Pau_Monn=E9?= wrote:
} Subject: Re: [Xen-devel] iSCSI connection corrupts Xen block devices.

> On 26/03/13 07:26, Dr. Greg Wettstein wrote:
> > Hi, hope the week has started out well for everyone.
> > 
> > This report may be in the FWIW department since there may be a
> > fundamental reason why this doesn't work.  We elected to report this
> > to the Xen community since we thought any behavior which corrupted
> > disk images needed to at least be reported.

> Hello Greg,

Hi Roger, thanks for taking time to respond.  A thank you also to
Konrad for his reply.

> I've also noticed this some time ago, the cause of this bug is that
> we pass granted pages to netback, and when trying to perform the
> grant copy operation it fails. I've sent a clumsy patch that solved
> the problem, but it involves additional memcpy in order to avoid
> passing the granted page to netback:
>
> http://lists.xen.org/archives/html/xen-devel/2013-01/msg00717.html
>
> The best solution I can think of is storing the grant frame
> reference somewhere in the p2m table, and then using that reference
> instead of the mfn when performing the grant copy operation.

So it is definitely an issue of, "If it hurts then don't do that".

I had the sense, that expecting things to work right when pages were
transiting multiple instances and types of backends, may have been
optimistic.  It is somewhat of an edge case application so it would
seem reasonable to wait on wading into a fix until all the persistent
grant work has been completed.

On the other hand it may be worth tossing something into a FAQ
someplace since it does violate the concept of least surprise.

> Regards, Roger.

Thanks for the clarifications, have a good weekend.

Greg

}-- End of excerpt from =?ISO-8859-1?Q?Roger_Pau_Monn=E9?=

As always,
Dr. G.W. Wettstein, Ph.D.   Enjellic Systems Development, LLC.
4206 N. 19th Ave.           Specializing in information infra-structure
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