Hello all, I am trying to understand how a virtio-block device updates "used" buffers in the virtqueue. I intend to 'mimic' this process without the actual disk event happening, by storing the used buffers and then re-using them later. I can see that the function *virtqueue_fill *is primarily responsible for filling up the virtqueue which eventually updates the guest memory. *vring_used_write* eventually does a memcpy to write the used buffer contents to the memory.
I do not understand what is the primary role of the *virtqueue_unmap_sg* function. I have a few questions. - What does this function do? - Does it in any way modify the guest's physical memory? - Why do we need to map and unmap the in_sg and out_sg into/out of the DMA address space? Is this for updating the IOMMU and destroying the address mappings that existed before? - What happens if unmapping does not happen? If there are good articles that describe this process of DMA address space mapping/unmapping, feel free to point me to them and I would love to read them too. Thank you very much. Best Regards, Arnabjyoti Kalita
