Adding or Customizing a Distribution

Contents:

Introduction [edit section]

Although Fuego is configured to execute on a standard Linux distribution, Fuego supports customizing certain aspects of its interaction with the system under test. Fuego uses several features of the operating system on the board to perform aspects of its test execution. This includes things like accessing the system log, flushing file system caches, and rebooting the board. The ability to customize Fuego's interaction with the system under test is useful in case you have a non-standard Linux distribution (where, say, certain features of Linux are missing or changed), or when you are trying to use Fuego with a non-Linux system.

A developer can customize the distribution layer of Fuego in one of two ways:

Distribution overlay file [edit section]

A distribution overlay file can be added to Fuego, by adding a new .dist file to the directory: fuego-core/overlays/distrib

The "distribution" functions are defined in the file: fuego-core/overlays/base/base-distrib.fuegoclass These include functions for doing certain operations on your board, including:

You can define your own "distribution" overlay by defining a new ".dist" file in fuego-core/overlays/distribs. (e.g. mydist.dist) Basically, you inherit functions from base-distrib.fuegoclass, and write override functions in mydist.dist to perform those operations the way they need to be done on your distribution.

You can look up what each override function should do by reading the fuegoclass code, or looking at the function documentation at: Test Script APIs

The inheritance mechanism and syntax for Fuego overlay files is described at: Overlay Generation

The goal of the distribution abstraction layer in Fuego is to allow you to customize Fuego operations to match what is available on your target board. For example, the default (base class) ov_rootfs_logread() function assumes that the target board has the command "/sbin/logread" that can be used to read the system log. If your distribution does not have "/sbin/logread", or indeed if there is no system log, then you would need to override ov_rootfs_logread() to do something appropriate for your distribution or OS.

Note: In fact, this is a common enough situation that there is already a 'nologread.dist' file already in the overlay/distribs directory.

Similarly, ov_rootfs_kill() uses the /proc filesystem, /proc/$pid/status, and the cat, grep, kill and sleep commands on the target board to do its work. If our distribution is missing any of these, then you would need to override ov_rootfs_kill() with a function that did the appropriate thing on your distribution (or OS).

Existing distribution overlay files [edit section]

Fuego provides a few distribution overlay files for certain situations that commonly occur in embedded Linux testing.

Referencing the distribution in the board file [edit section]

Inside the board file for your board, indicate the distribution overlay you are using by setting the "DISTRIB" variable.

If the DISTRIB variable is not set, then the default distribution overlay functions are used.

For example, if your embedded distribution of Linux does not have a system logger, you can override the normal logging interaction of Fuego by using the 'nosyslogd.dist' distribution overlay. To do this, add the following line to the board file for target board where this is the case:

Testing Fuego/distribution interactions [edit section]

There is a test you can run to see if the minimal command set required by Fuego is supported on your board. It does not require a toolchain, since it only runs shell script code on the board. The test is Functional.fuego_board_check.

This test may work on your board, if your board supports a POSIX shell interface. However, note that this test reflects the commands that are used by Fuego core and by the default distribution overlay. If you make your own distribution overlay, you may want to create a version of this test that omits checks for things that your distribution does not support, or that adds checks for things that your distribution overlay uses to interact with the board.

Notes [edit section]

Fuego does not yet fully support testing non-Linux operating systems. There is work-in-progress to support testing of NuttX, but that feature is not complete as of this writing. In any event, Fuego does include a 'NuttX' distribution overlay, which may provide some ideas if you wish to write your own overlay for a non-Linux OS.

NuttX distribution overlay [edit section]

By way of illustration, here are the contents of the NuttX distribution overlay file (fuego-core/overlays/distribs/nuttx.dist). 

override-func ov_get_firmware() {
    FW="$(cmd uname -a)"
}

override-func ov_rootfs_reboot() {
    cmd "reboot"
}

override-func ov_init_dir() {
    # no-op
    true
}

override-func ov_remove_and_init_dir() {
    # no-op
    true
}

override-func ov_rootfs_state() {
    cmd "echo; date; echo; free; echo; ps; echo; mount" || \
        abort_job "Error executing rootfs_status operation on target"
}

override-func ov_logger() {
    # messages are in $@, just emit them
    echo "Fuego log messages: $@"
}

# $1 = tmp dir, $2 = before or after
override-func ov_rootfs_logread() {
    # no-op
    true
}

override-func ov_rootfs_sync() {
    # no-op
    true
}

override-func ov_rootfs_drop_caches() {
    # no-op
    true
}

override-func ov_rootfs_oom() {
    # no-op
    true
}

override-func ov_rootfs_kill() {
    # no-op
    true
}

Hypothetical QNX distribution [edit section]

Say you wanted to add support for testing QNX with Fuego.

Here are some first steps to add a QNX distribution overlay: