STorage Appliance Services (STAS)

What does nvme-stas provide?

• A Central Discovery Controller (CDC) client for Linux
• Asynchronous Event Notifications (AEN) handling
• Automated NVMe subsystem connection controls
• Error handling and reporting
• Automatic (zeroconf) and Manual configuration

Overview

STAS is composed of two services, STAF and STAC, running on the Host computer.

STAF - STorage Appliance Finder. The tasks performed by STAF include:

• Register with the Avahi daemon for service type _nvme-disc._tcp. This allows STAF to locate Central or Direct Discovery Controllers (CDC, DDC) with zero-touch provisioning (ZTP). STAF also allows users to manually enter CDCs and DDCs in a configuration file (/etc/stas/stafd.conf) when users prefer not to use ZTP.
• Connect to discovered or configured CDCs or DDCs.
• Retrieve the list of storage subsystems using the "get log page" command.
• Maintain a cache of the discovered storage subsystems.
• Provide a D-Bus interface where 3rd party applications can retrieve the data about the Discovery Controller connections (e.g. log pages).

STAC - STorage Appliance Connector. The tasks performed by STAC include:

• Read the list of storage subsystems from STAF over D-Bus.
• Similar to STAF, STAC can also read a list of storage subsystems to connect to from a configuration file.
• Set up the I/O controller connections.
• Provide a D-Bus interface where 3rd party applications can retrieve data about the I/O controller connections.

Design

stafd and stacd use the GLib main loop. The GLib Python module provides several low-level building blocks that are needed by stafd and stacd. In addition, many Python modules "play nice" with GLib such as dasbus and pyudev. GLib also provides additional components such as timers, signal handlers, and much more.

stafd connects to the avahi-daemon, which it uses to detect Central Discovery Controllers (CDC) and Direct Discovery Controllers (DDC). When Discovery Controllers (DC) are found with Avahi's help, stafd uses libnvme to set up persistent connections and retrieve the discovery log pages.

Daemonization

stafd and stacd are managed as systemd services. The following operations are supported (here showing only stafd, but the same operations apply to stacd):

• systemctl start stafd. Start daemon.
• systemctl stop stafd. Stop daemon. The SIGTERM signal is used to tell the daemon to stop.
• systemctl restart stafd. Effectively a stop + start.
• systemctl reload stafd. Reload configuration. This is done in real time without restarting the daemon. The SIGHUP signal is used to tell the daemon to reload its configuration file.

Configuration

As stated before, stafd can automatically locate discovery controllers with the help of Avahi and connect to them, and stacd can automatically set up the I/O connections to discovered storage subsystems. However, stafd and stacd can also operate in a non-automatic mode based on manually entered configuration. In other words, discovery controllers and/or storage subsystems can be entered manually. This is to provide customers with more flexibility. The configuration for each daemon is found in /etc/stas/stafd.conf and /etc/stas/stacd.conf respectively. The configuration files also provide additional parameters, such as log-level attributes used mainly for debugging purposes.

The following configuration files are defined:

File	Consumer	Purpose
/etc/stas/sys.conf	stafd + stacd	Contains system-wide (i.e. host) configuration such as the Host NQN, the Host ID, and the Host Symbolic Name. Changes to this file can be made manually or with the help of the stasadm utility as described in the previous section. For example, stasadm hostnqn -f /etc/nvme/hostnqn writes the Host NQN to the file /etc/nvme/hostnqn, but also adds an entry to /etc/stas/sys.conf to indicate where the Host NQN has been saved. This gives nvme-stas the flexibility of defining its own Host parameters or to use the same parameters defined by libnvme and nvme-cli.
/etc/stas/stafd.conf	stafd	Contains configuration specific to stafd. Discovery controllers can be manually added or blacklisted in this file.
/etc/stas/stacd.conf	stacd	Contains configuration specific to stacd. I/O controllers can be manually added or blacklisted in this file.

D-Bus interface

The interface to stafd and stacd is D-Bus. This allows other programs, such as stafctl and stacctl, to communicate with the daemons. This also provides third parties the ability to write their own applications that can interact with stafd and stacd. For example, someone could decide to write a GUI where they would display the discovery controllers as well as the all the discovery log pages in a "pretty" window. The next table provides info about the two D-Bus interfaces.

Component	D-Bus address
stafd	org.nvmexpress.staf.conf
stacd	org.nvmexpress.stac.conf

Companion programs: stafctl and stacctl

stafctl and stacctl are utilities that allow users to interact with stafd and stacd respectively. This is a model used by several programs, such as systemctl with systemd.

At a minimum, these utilities provide debug tools, but they could also provide some configuration capabilities (TBD).

Packages

stafd and stacd as well as their companion programs stafctl and stacctl are released together in a package called "nvme-stas" for STorage Applicance Services (e.g. stas-1.0.0-1.x86_64.rpm or stas_1.0.0_amd64.deb).

Dependencies

stafd/stacd require Linux kernel 5.14 or later.

The following packages must be installed to use stafd/stacd

Debian packages (tested on Ubuntu 20.04):

sudo apt-get install -y python3-pyudev python3-systemd python3-gi
sudo pip3 install dasbus

RPM packages (tested on Fedora 34..35 and SLES15):

sudo dnf install -y python3-dasbus python3-pyudev python3-systemd python3-gobject

STAF - STorage Appliance Finder

Component	Description
/usr/sbin/stafd	A daemon that finds (discovers) NVMe storage appliances.
/usr/bin/stafctl	A companion shell utility for stafd.
/etc/stas/stafd.conf	Configuration file

stafd configuration file

The configuration file is named /etc/stas/stafd.conf. This file contains configuration parameters for the stafd daemon. One of the things you may want to configure is the IP address of the discovery controller(s) you want stafd to connect to. The configuration file contains a description of all the parameters that can be configured.

Service discovery with Avahi

stafd can automatically find and set up connections to Discovery Controllers. To do this, stafd registers with the Avahi, the mDNS/DNS-SD (Service Discovery) daemon. Discovery Controllers that advertise themselves with service type _nvme-disc._tcp will be recognized by Avahi, which will inform stafd.

Not receiving mDNS packets?

If stafd is not detecting any discovery controllers through Avahi, it could simply be that the mDNS packets are being suppressed by your firewall. If you know for a fact that the discovery controllers are advertizing themselves with mDNS packets, make sure that the Avahi daemon is receiving them as follows:

avahi-browse -r _nvme-disc._tcp

If you're not seeing anything, then check whether your firewall allows mDNS packets.

Why is Avahi failing to discover services on some interfaces?

Linux limits the number of multicast group memberships that a host can belong to. The default is 20. For Avahi to monitor mDNS (multicast DNS) packets on all interfaces, the host computer must be able to register one multicast group per interface. This can be physical or logical interfaces. For example, configuring 10 VLANs on a physical interface increases the total number of interfaces by 10. If the total number of interfaces is greater than the limit of 20, then Avahi won't be able to monitor all interfaces.

The limit can be changed by configuring the variable igmp_max_memberships. This variable is defined here in the kernel documentation. And this StackExchange page describes how one can increase the limit.

STAC - STorage Appliance Connector

File name	Description
/usr/sbin/stacd	A daemon that connects to NVMe storage appliances.
/usr/bin/stacctl	A companion shell utility for stacd.
/etc/stas/stacd.conf	Configuration file

stacd configuration file

The configuration file is named /etc/stas/stacd.conf. In this file you can configure storage appliances that stacd will connect to. By default, stacd uses information (log pages) collected from stafd to connect to storage appliances. However, you can also manually enter IP addresses of storage appliances in this file.

System configuration

A host must be provided with a Host NQN and a Host ID. nvme-stas will not run without these two mandatory configuration parameters. To follow in the footsteps of nvme-cli and libnvme, nvme-stas will use the same Host NQN and ID that nvme-cli and libnvme use by default. In other words, nvme-stas will read the Host NQN and ID from these two files by default:

1. /etc/nvme/hostnqn
2. /etc/nvme/hostid

Using the same configuration files will ensure consistency between nvme-stas, nvme-cli, and libnvme. On the other hand, nvme-stas can operate with a different Host NQN and/or ID. In that case, one can specify them in /etc/stas/sys.conf.

A new optional configuration parameters introduced in TP8010, the Host Symbolic Name, can also be specified in /etc/stas/sys.conf. The schema/documentation for /etc/stas/sys.conf can be found /etc/stas/sys.conf.doc.

Build, install, unit tests

STAS uses the meson build system. Since STAS is a Python project, there is no code to build. However, the code needs to be installed using meson. Unit tests can also be run with meson.

Using meson

Invoke meson to configure the project:

meson .build

The command meson .build need only be called once. This analyzes the project and the host computer to determine if all the necessary tools and dependencies are available. The result is saved to the directory named .build.

To compile the code:

cd .build
ninja

To install / uninstall the code:

cd .build
meson install
ninja uninstall

To run the unit tests:

cd .build
meson test

For more information about testing, please refer to: TESTING.md

Alternate approach using Good-ole make

Recognizing that many people are not familiar with meson, we're providing a second way to install the code using the more familiar configure script combined with a make.

./configure
make

This performs the same operations as the meson approach described above. The configure script is automatically invoked when running make by itself.

make command	Description
make	Invoke the .configure script and build the code.
make install	Install the code. Requires root privileges (you will be asked to enter your password).
make uninstall	Uninstall the code. Requires root privileges (you will be asked to enter your password).
make test	Run the unit tests
make clean	Clean build artifacts, but does not remove the meson's configuration. That is, the configuration in .build is preserved.
make purge	Remove all build artifacts including the .build directory.

Compiling and running nvme-stas in a docker container

Use published image (optional)

docker pull ghcr.io/linux-nvme/nvme-stas:main

Build your own image (optional)

docker-compose up --build

Run services using docker-compose like this

docker-compose up

Run companion programs stafctl and stacctl like this

docker-compose exec stafd stafctl ls
docker-compose exec stafd stafctl status

docker-compose exec stacd stacctl ls
docker-compose exec stacd stacctl status

dependencies: dbus, avahi.

Generating man and html pages

nvme-stas uses the following programs to generate the documentation. These can be installed as shown in the "dependencies" section below.

• xsltproc - Used to convert DocBook XML notation to "man pages" and "html pages".
• gdbus-codegen - Used to convert D-Bus IDL to DocBook XML notation.

Dependencies

The following packages must be installed to generate the documentation

Debian packages (tested on Ubuntu 20.04):

sudo apt-get install -y docbook-xml docbook-xsl xsltproc libglib2.0-dev

RPM packages (tested on Fedora 34..35 and SLES15):

sudo dnf install -y docbook-style-xsl libxslt glib2-devel

Configuring and building the man and html pages

By default, the documentation is not built. You need to run the configure as follows to tell meson that you want to build the documentation. You may need to first purge any previous configuration.

make purge
./configure -Dman=true -Dhtml=true
make

Generating RPM and/or DEB packages

make rpm deb