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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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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