Messages in this thread | | | Date | Wed, 14 Aug 2013 17:41:49 +0100 | From | Stefano Stabellini <> | Subject | Re: [PATCH v3 07/10] xen: introduce XENMEM_get_dma_buf and xen_put_dma_buf |
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On Fri, 9 Aug 2013, Konrad Rzeszutek Wilk wrote: > > > +struct xen_get_dma_buf { > > > + /* > > > + * [IN] Details of memory extents to be exchanged (GMFN bases). > > > + * Note that @in.address_bits is ignored and unused. > > > > Ohhhh, why? What if the user wants to be it under 2G? > > Looking a bit more at the code revealed that we stick that in the > @out.address_bits > > > > > + */ > > > + struct xen_memory_reservation in; > > > + > > > + /* > > > + * [IN/OUT] Details of new memory extents. > > > + * We require that: > > > + * 1. @in.domid == @out.domid > > > + * 2. @in.nr_extents << @in.extent_order == > > > + * @out.nr_extents << @out.extent_order > > > + * 3. @in.extent_start and @out.extent_start lists must not overlap > > > + * 4. @out.extent_start lists GPFN bases to be populated > > > + * 5. @out.extent_start is overwritten with allocated GMFN bases > > .. which you should document, otherwise the hypervisor might try to give > you pages under 2^0..
Yes, you are right. I'll add a note about out.address_bits.
> > > + */ > > > + struct xen_memory_reservation out; > > > + > > > + /* > > > + * [OUT] Number of input extents that were successfully exchanged: > > > + * 1. The first @nr_exchanged input extents were successfully > > > + * deallocated. > > > + * 2. The corresponding first entries in the output extent list correctly > > > + * indicate the GMFNs that were successfully exchanged. > > > + * 3. All other input and output extents are untouched. > > > + * 4. If not all input exents are exchanged then the return code of this > > > + * command will be non-zero. > > > + * 5. THIS FIELD MUST BE INITIALISED TO ZERO BY THE CALLER! > > as this says the initial value is zero.
This is referring to nr_exchanged.
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