Re: [Qemu-block] [PATCH 3/4] util: Add VFIO helper library

[Paolo Bonzini]

On 20/12/2016 17:31, Fam Zheng wrote:
> +    hbitmap_iter_init(&iter, s->free_chunks, 1);
> +    if (contiguous) {
> +        while (true) {
> +            bool satisfy = true;
> +            next = hbitmap_iter_next(&iter);
> +            if (next < 0) {
> +                return NULL;
> +            }
> +            for (i = 1; i < chunks; i++) {
> +                if (!hbitmap_get(s->free_chunks, next + i)) {
> +                    satisfy = false;
> +                    break;
> +                }
> +            }
> +            if (satisfy) {
> +                break;
> +            }
> +        }
> +        hbitmap_reset(s->free_chunks, next, chunks);
> +        r = g_new(IOVARange, 1);
> +        r->iova = next * pages_per_chunk * getpagesize();
> +        r->nr_pages = pages;
> +        QSIMPLEQ_INSERT_TAIL(&m.iova_list, r, next);
> +    } else {
> +        next = hbitmap_iter_next(&iter);
> +        while (pages) {
> +            uint64_t chunk;
> +            if (next < 0) {
> +                hbitmap_iter_init(&iter, s->free_chunks, 1);
> +                next = hbitmap_iter_next(&iter);
> +            }
> +            assert(next >= 0);
> +            chunk = next;
> +            DPRINTF("using chunk %ld\n", chunk);
> +            next = hbitmap_iter_next(&iter);
> +            hbitmap_reset(s->free_chunks, chunk, 1);
> +            if (r && r->iova + r->nr_pages == chunk * pages_per_chunk) {
> +                r->nr_pages += MIN(pages, pages_per_chunk);
> +            } else {
> +                r = g_new(IOVARange, 1);
> +                r->iova = chunk * pages_per_chunk * getpagesize();
> +                r->nr_pages = MIN(pages, pages_per_chunk);
> +                QSIMPLEQ_INSERT_TAIL(&m.iova_list, r, next);
> +            }
> +            pages -= MIN(pages, pages_per_chunk);
> +        }

I'm not sure HBitmap tracking is useful.  If we exhaust the IOVA space,
we can just throw everything away with a single VFIO_IOMMU_UNMAP_DMA.
Then replay the RAMBlockNotifier mappings (we need to add this anyway
for hotplug support) and keep on mapping lazily whatever comes later.

Thanks,

Paolo