Blobstore and BlobFS

The blobstore is a persistent, power-fail safe block allocator designed to be
used as the local storage system backing a higher-level storage service.
See the blobstore documentation for more details.

BlobFS adds basic filesystem functionality like filenames on top of the blobstore.
This release also includes a RocksDB Env implementation using BlobFS in place of the
kernel filesystem.
See the BlobFS documentation for more details.

Userspace vhost-scsi target

A userspace implementation of the QEMU vhost-scsi protocol has been added.
The vhost target is capable of exporting SPDK bdevs to QEMU-based VMs as virtio devices.
See the vhost documentation for more details.

Event framework

The overhead of the main reactor event loop was reduced by optimizing the number of
calls to spdk_get_ticks() per iteration.

NVMe library

The NVMe library will now automatically split readv/writev requests with scatter-gather
lists that do not map to valid PRP lists when the NVMe controller does not natively
support SGLs.

The identify and perf NVMe examples were modified to add a consistent format for
specifying remote NVMe over Fabrics devices via the -r option.
This is implemented using the new spdk_nvme_transport_id_parse() function.

iSCSI Target

The [Nvme] section of the configuration file was modified to remove the BDF directive
and replace it with a TransportID directive. Both local (PCIe) and remote (NVMe-oF)
devices can now be specified as the backing block device. A script to generate an
entire [Nvme] section based on the local NVMe devices attached was added at
scripts/gen_nvme.sh.

NVMe-oF Target

The [Nvme] section of the configuration file was modified to remove the BDF directive
and replace it with a TransportID directive. Both local (PCIe) and remote (NVMe-oF)
devices can now be specified as the backing block device. A script to generate an
entire [Nvme] section based on the local NVMe devices attached was added at
scripts/gen_nvme.sh.