Presenting paravirtualized devices to virtual machines has historically required specialized drivers to be present in the guest operating system. The most popular example is virtio-blk or virtio-scsi. These devices can be constructed using either the host system operating system (KVM, for example, can emulate virtio-blk and virtio-scsi devices for use by the guest) or by a separate user-space process (the vhost-user protocol can connect to these targets, typically provided by SPDK). However, only Linux currently ships with virtio-blk and virtio-scsi drivers built-in.

Writing a storage network server based on TCP sockets seems straightfoward - you call send() and recv() on the socket and parse the data. But the reality is not so simple. For example, most people know that sockets should be grouped together to make polling the set more efficient via epoll, kqueue, or io_uring. But did you know that it matters which sockets are grouped together, and that there's at least three different ways to group them?