[Week 4] Import the Xen grant-table bus_dma(9) handlers from OpenBSD

[Pratyush Yadav]

Hi,

This week I finished up my implementation of the xen-specific
bus_dma(9) handlers. I asked Roger Pau Monne for review. After his
review, I realized I had been doing things a little wrong. I was
building the Xen-specific handlers on top of the bus_dma(9) interface.
Instead, I should have created an alternate busdma implementation,
kind of like sys/x86/iommu/busdma_dmar.c

So I had to study the inner details of the bus_dma(9) interface to
learn how an alternate implementation can be written. This was a
little confusing at the beginning.because there is no clear guide on
the subsystem for beginners like me. But eventually, I got the hang of
it, mostly by reading code already written.

After that came the task of rewriting my implementation. I wrote it,
and then spent a couple of days refining it. Today, I submitted it to
Roger again for review. We are discussing it as of now. No major
concerns have been raised so I should be done with the xen-specific
busdma hooks in a few days.

You can check out the code at [0].

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 [1].


[0] https://github.com/prati0100/freebsd

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

-- 
Regards,
Pratyush Yadav