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Re: [Xen-devel] passing hypercall parameters by pointer

On 19 Aug 2005, at 14:57, Hollis Blanchard wrote:

Could you flesh this out a little more? I *think* what you're saying is this (on PowerPC):
- at boot, the kernel notifies Xen of a parameter page

It can be multiple pages, and the mappings can change over time. Think of something like set_parameter_page(parameter_address_space_frame, physical_address_space_fram) establishing a mapping from parameter address space to phys address space.

- replace libxc calls to mlock() with register_this_address() (which could be a privcmd ioctl)

Yep. I think libxc would request via a privcmd ioctl. The kernel can extend the parameter-passing region, or allocate a subsection of the existing region, and mmap it into user space. It would also return to libxc the range of parameter-passing addresses that have been allocated to it.

- libxc ignorantly creates its structures with userspace addresses

libxc would create structs with parameter-passing addresses.

 -- Keir

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