Add porting guide.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: Ic028d9d776b094fc2fa048c23424aec2c8434cc6

PORTING.md

@@ -0,0 +1,23 @@
+SPDK Porting Guide
+==================
+
+SPDK is ported to new environments by implementing the nvme_impl
+interface.  The nvme_impl interface provides APIs for the driver
+to allocate physically contiguous and pinned memory, perform PCI
+operations (config cycles and mapping BARs), virtual to physical
+address translation and allocating per I/O data structures.
+
+SPDK includes a default implementation of the nvme_impl API based
+on the Data Plane Development Kit ([DPDK](dpdk.org)) and
+libpciaccess.  This DPDK implementation can be found in
+lib/nvme/nvme_impl.h.  DPDK is currently supported on Linux and
+FreeBSD only.
+
+Users who want to use SPDK on other operating system, or in
+userspace driver frameworks other than DPDK, will need to implement
+a new version of nvme_impl.h.  The new nvme_impl.h can be
+integrated into the SPDK build by updating the following line
+in CONFIG:
+
+    CONFIG_NVME_IMPL=nvme_impl.h
+

README.md

@@ -11,6 +11,8 @@ userspace and operating in a polled mode instead of relying on interrupts,
 which avoids kernel context switches and eliminates interrupt handling
 overhead.
 
+[Porting Guide](PORTING.md)
+
 Prerequisites
 =============