[Week 2] Import the Xen grant-table bus_dma(9) handlers from OpenBSD

[Pratyush Yadav]

Hi,

I spent this week on writing rough initial implementations of the
Xen-specific grant table handlers imported from OpenBSD. I spent a lot
of time understanding the differences in OpenBSD and FreeBSD's
grant-table interface. They turn out to be more different than I
anticipated.

After that we encountered some design decisions. Since the bus_dma(9)
interface in FreeBSD is quite different from the OpenBSD counterpart,
some design choices had to be made. I am still in talks with my
mentors about it.

I also produced rough implementations of the grant table handlers.
These are not yet complete. There are a lot of rough edges to polish.
Check out the implementations in my GitHub fork [0].

Unrelated to the project, I submitted a diff to remove some leftover
function prototypes from the grant table header file gnttab.h [1].

I maintain a blog on Blogger where I publish my progress every few
days. Check it out if you want more details on what I'm doing [2].

Regards,
Pratyush Yadav

[0] https://github.com/prati0100/freebsd/tree/projects/xen_bus_dma

[1] https://reviews.freebsd.org/D15553

[2] http://pratyushgsoc.blogspot.in/2018/05/import-xen-grant-table-busdma9-handlers.html