doc: Add initial documentation for nvme hotplug.

Change-Id: I67303d07aee931d19b3a9ae1e618d22fc6de9f58
Signed-off-by: Cunyin Chang <cunyin.chang@intel.com>

doc/Doxyfile

@@ -772,6 +772,7 @@ INPUT                  = ../include/spdk \
                          nvme/async_completion.md \
                          nvme/fabrics.md \
                          nvme/initialization.md \
+                         nvme/hotplug.md \
                          nvme/io_submission.md \
                          nvme/multi_process.md \
                          nvmf/index.md \

doc/nvme/hotplug.md

@@ -0,0 +1,19 @@
+# NVMe Hotplug {#nvme_hotplug}
+
+At the NVMe driver level, we provide the following support for Hotplug:
+
+1. Hotplug events detection:
+The user of the NVMe library can call spdk_nvme_probe() periodically to detect
+hotplug events. The probe_cb, followed by the attach_cb, will be called for each
+new device detected. The user may optionally also provide a remove_cb that will be
+called if a previously attached NVMe device is no longer present on the system.
+All subsequent I/O to the removed device will return an error.
+
+2. Hot remove NVMe with IO loads:
+When a device is hot removed while I/O is occurring, all access to the PCI BAR will
+result in a SIGBUS error. The NVMe driver automatically handles this case by installing
+a SIGBUS handler and remapping the PCI BAR to a new, placeholder memory location.
+This means I/O in flight during a hot remove will complete with an appropriate error
+code and will not crash the application.
+
+@sa spdk_nvme_probe

doc/nvme/index.md

@@ -24,3 +24,4 @@ spdk_nvme_ctrlr_process_admin_completions() | @copybrief spdk_nvme_ctrlr_process
 - @ref nvme_async_completion
 - @ref nvme_fabrics_host
 - @ref nvme_multi_process
+- @ref nvme_hotplug