Re: [PATCH v3 4/5] vhost-user-dev: Add cache BAR

[Stefan Hajnoczi]

On Thu, Sep 12, 2024 at 04:53:34PM +0200, Albert Esteve wrote:
> @@ -331,6 +333,37 @@ static void vub_device_realize(DeviceState *dev, Error 
> **errp)
>          do_vhost_user_cleanup(vdev, vub);
>      }
>  
> +    ret = vub->vhost_dev.vhost_ops->vhost_get_shmem_config(&vub->vhost_dev,
> +                                                           &nregions,
> +                                                           memory_sizes,
> +                                                           errp);
> +
> +    if (ret < 0) {
> +        do_vhost_user_cleanup(vdev, vub);
> +    }
> +
> +    for (i = 0; i < nregions; i++) {
> +        if (memory_sizes[i]) {
> +            if (memory_sizes[i] % qemu_real_host_page_size() != 0) {
> +                error_setg(errp, "Shared memory %d size must be a power of 2 
> "
> +                                 "no smaller than the page size", i);
> +                return;
> +            }
> +
> +            cache_ptr = mmap(NULL, memory_sizes[i], PROT_NONE,
> +                            MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +            if (cache_ptr == MAP_FAILED) {
> +                error_setg_errno(errp, errno, "Unable to mmap blank cache");
> +                return;
> +            }
> +
> +            virtio_new_shmem_region(vdev);
> +            memory_region_init_ram_ptr(vdev->shmem_list[i].mr,

I don't think this works because virtio_new_shmem_region() leaves .mr =
NULL? Why allocates the MemoryRegion and assigns it to shmem_list[i].mr?

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