All, I have been looking at one of the TODO items in the Linux Hyper-V drivers. Specifically the one that says; - remove RingBuffer.c to use in-kernel ringbuffer functions instead. I spend some time figuring out the ring buffer capability inside of the Linux Kernel to see if we could change the Hyper-V ring buffer out for the in-kernel ring buffer capability. The ring buffer in the Hyper-V Linux drivers is used to communicate with the parent partition running Server 2008 Hyper-V. The ring buffer functionality on the Hyper-V Linux drivers is written to be functionally compatible with" the ring buffer functionality on the Hyper-V Server. Consequently, it is not possible to make any changes that might break the compatibility with server side ring buffer implementation. 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. 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? As usual, any help is appreciated. Thanks, Hank Janssen.
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. J
On Wed, Mar 03, 2010 at 04:42:27PM +0000, Hank Janssen wrote:> The ring buffer in the Hyper-V Linux drivers is used to communicate with the > parent partition running Server 2008 Hyper-V. The ring buffer functionality on > the Hyper-V Linux drivers is written to be functionally compatible with" the > ring buffer functionality on the Hyper-V Server. Consequently, it is not > possible to make any changes that might break the compatibility with server > side ring buffer implementation.Ok, that makes sense, feel free to remove that TODO item. thanks for looking into this. greg k-h