Re: Ringbuffer usage in Linux Hyper-V drivers

From: Jeremy Fitzhardinge
Date: Wed Mar 03 2010 - 12:49:13 EST

On 03/03/2010 08:42 AM, Hank Janssen wrote:
There is a pretty good chance that ring buffer on Hyper-V will change to support
additional functionality. I did further investigations to check on other
virtualization technologies. And this same things seems to be true for XEN,
they also implemented their own ring buffer implementation on the guest side
because of their host side implementation.

Yes. The cross-domain producer-consumer ringbuffer is a pretty specific protocol. Not only is the data format an ABI, but the exact protocol for what pointers get updated when, etc. Its not at all obvious how we could reuse the kernel ringbuffer implementation, since it assumes its implementing both the producer and consumer ends.

So my question is to the community at large, am I missing something that would
enable me to use an existing ring buffer functionality somehow in the kernel?
If not, I want to remove the line from the TODO file that is requesting to use the
in-kernel ring buffer functionality.

Finally, while checking this out, I looked at a bunch of non virtualization device
drivers currently in the kernel. And all the ones I looked at have
implemented their own ring buffer. Is there a reason why this might be the case?

linux/ring_buffer.h is relatively new, and probably post-dates most of the driver ringbuffers. If the ringbuffer is entirely within the kernel (say, between an ISR and the rest of the kernel) then I guess it might be possible to use the standard functions. But if half the ringbuffer is being managed by the device itself, then that will define the protocol.

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