Re: [Xen-devel] [PATCHv2 0/2] xen/privcmd: support for paged-out frames

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-08-29 at 17:56 +0100, David Vrabel wrote:
> On 29/08/12 17:23, Ian Campbell wrote:
> > On Wed, 2012-08-29 at 14:15 +0100, David Vrabel wrote:
> >> This series is a straight forward-port of some functionality from
> >> classic kernels to support Xen hosts that do paging of guests.
> >>
> >> This isn't functionality the XenServer makes use of so I've not tested
> >> these with paging in use.
> >>
> >> Changes since v1:
> >>
> >> - Don't change PRIVCMD_MMAPBATCH (except to #define a constant for the
> >>   error).  It's broken and not really fixable sensibly and libxc will
> >>   use V2 if it is available.
> >> - Return -ENOENT if all failures were -ENOENT.
> > 
> > Is this behaviour a requirement from something?
> 
> It's the behaviour libxc is expecting.  It doesn't retry unless errno ==
> ENOENT.

Surely if that is the case you must return -ENOENT if *any* failure was
-ENOENT? That seems to be what the linux-2.6.18-xen.hg implementation
does.

> > Usually hypercalls of this type return a global error only if something
> > went wrong with the general mechanics of the hypercall (e.g. faults
> > reading arguments etc) and leave reporting of the individual failures of
> > subops to the op specific field, even if all the subops fail in the same
> > way.
> 
> I didn't design this interface...

The interface you described doesn't make any sense so I was trying to
suggest a way in which you may have misunderstood the interface you were
trying to implement by pointing out the common pattern. It turns out
this interface doesn't follow that common pattern, but it's still
different to what you described AFAICT.

> Feel free to propose (and implement) an alternate MMAPBATCH_V3 interface.

No thanks ;-)

Ian.


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