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doc: Expand the intro section of the bdev documentation.

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Change-Id: I2077133fc8f98d1fc1020d617e50867871d8e841
Signed-off-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-on: https://review.gerrithub.io/392986
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Daniel Verkamp <daniel.verkamp@intel.com>
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Ben Walker 2017-12-26 14:37:58 -07:00 committed by Jim Harris
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# Block Device Abstraction Layer {#bdev}
# Block Device Layer {#bdev}
# SPDK bdev Getting Started Guide {#bdev_getting_started}
# Introduction {#bdev_getting_started}
Block storage in SPDK applications is provided by the SPDK bdev layer. SPDK bdev consists of:
The SPDK block device layer, often simply called *bdev*, is a C library
intended to be equivalent to the operating system block storage layer that
often sits immediately above the device drivers in a traditional kernel
storage stack. Specifically, this library provides the following
functionality:
* a driver module API for implementing bdev drivers
* an application API for enumerating and claiming SPDK block devices and performance operations
(read, write, unmap, etc.) on those devices
* bdev drivers for NVMe, malloc (ramdisk), Linux AIO and Ceph RBD
* configuration via SPDK configuration files or JSON RPC
* A pluggable module API for implementing block devices that interface with different types of block storage devices.
* Driver modules for NVMe, malloc (ramdisk), Linux AIO, virtio-scsi, Ceph RBD, and more.
* An application API for enumerating and claiming SPDK block devices and then performing operations (read, write, unmap, etc.) on those devices.
* Facilities to stack block devices to create complex I/O pipelines, including logical volume management (lvol) and partition support (GPT).
* Configuration of block devices via JSON-RPC and a configuration file.
* Request queueing, timeout, and reset handling.
* Multiple, lockless queues for sending I/O to block devices.
# Configuring block devices {#bdev_config}
SPDK block devices are typically configured via an SPDK configuration file. These block devices
can then be associated with higher level abstractions such as iSCSI target nodes, NVMe-oF namespaces
or vhost-scsi controllers. This section will describe how to configure block devices for the
SPDK bdev drivers included with SPDK.
The SPDK configuration file is typically passed to your SPDK-based application via the command line.
Refer to the help facility of your application for more details.
The block device layer is a C library with a single public header file named
bdev.h. Upon initialization, the library will read in a configuration file that
defines the block devices it will expose. The configuration file is a text
format containing sections denominated by square brackets followed by keys with
optional values. It is often passed as a command line argument to the
application. Refer to the help facility of your application for more details.
## NVMe {#bdev_config_nvme}