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Btrfs-progs tests

A testsuite covering functionality of btrfs-progs, ie. the checker, image, mkfs and similar tools. There are no additional requirements on kernel features (other than CONFIG_BTRFS_FS built-in or module), the tests build on top of the core functionality like snapshots and device management. In some cases optional features are turned on by mkfs and the filesystem image could be mounted, such tests might fail if there’s lack of support.

Quick start

Run the tests from the top directory:

$ make test
$ make test-fsck
$ make test-convert

or selectively from the tests/ directory:

$ ./fsck-tests.sh
$ ./misc-tests.sh

The verbose output of the tests is logged into a file named after the test category, eg. fsck-tests-results.txt.

Selective testing

The tests are prefixed by a number for ordering and uniqueness. To run a particular test use:

$ make TEST=MASK test

where MASK is a glob expression that will execute only tests that match the MASK. Here the test number comes handy:

$ make TEST=001\* test-fsck      # in tests/
$ TEST=001\* ./fsck-tests.sh     # in the top directory

will run the first test in fsck-tests subdirectory. If the test directories follow a good naming scheme, it’s possible to select a subset eg. like the convert tests for ext[234] filesystems using mask ‘TEST=’ext[234]’.

Test directory structure






tests/common, tests/common.convert


Other tuning, environment variables


It’s possible to wrap the tested commands to utilities that might do more checking or catch failures at runtime. This can be done by setting the INSTRUMENT environment variable:

make INSTRUMENT=valgrind test-fuzz     # in the top directory
INSTRUMENT=valgrind ./fuzz-tests.sh    # in tests/

The variable is prepended to the command unquoted, all sorts of shell tricks are possible.

Note: instrumentation is not applied to privileged commands (anything that uses the root helper), with exception of all commands built from git that will be instrumented even if run with the sudo helper.

run_check $SUDO_HELPER mount /dev/sdx /mnt           # no instrumentation
run_check $SUDO_HELPER "$TOP/btrfs" check /dev/sdx   # with instrumentation

Instrumented commands: btrfs, btrfs-image, btrfs-convert, btrfs-tune, mkfs.btrfs, btrfs-select-super, btrfs-find-root, btrfs-corrupt-block.

As mentioned above, instrumentation tools are like valgrind or potentially gdb with some init script that will let the commands run until an exception occurs, possibly allowing to continue interactively debugging.

Verbosity, test tuning

Multiple values can be separated by ,.

For example, running all fsck tests with the --mode=lowmem option can be done as

$ make TEST_ENABLE_OVERRIDE=true TEST_ARGS_CHECK=--mode=lowmem test-check

Specifically, fsck-tests that are known to be able to repair images in the lowmem mode shoulde be marked using a file .lowmem_repairable in the test directory. Then the fsck-tests with the ‘mode=lowmem’ will continue when image repair is requested.


Some commands require root privileges (to mount/umount, access loop devices or call privileged ioctls). It is assumed that sudo will work in some way (no password, password asked and cached). Note that instrumentation is not applied in this case, for safety reasons or because the tools refuse to run under root. You need to modify the test script instead.


The tests are supposed to cleanup after themselves if they pass. In case of failure, the rest of the tests are skipped and intermediate files, mounts and loop devices are kept. This should help to investigate the test failure but at least the mounts and loop devices need to be cleaned before the next run.

This is partially done by the script clean-tests.sh, you may want to check the loop devices as they are managed on a per-test basis, see the output of command losetup and eventually delete all existing loop devices with losetup -D.

Prototyping tests, quick tests

There’s a script test-console.sh that will run shell commands in a loop and logs the output with the testing environment set up. It sources the common helper scripts so the shell functions are available.

Runtime dependencies

The tests use some common system utilities like find, rm, dd. Additionally, specific tests need the following packages installed: acl, attr, e2fsprogs, reiserfsprogs.

New test

  1. Pick the category for the new test or fallback to misc-tests if not sure. For an easy start copy an existing test.sh script from some test that might be close to the purpose of your new test. The environment setup includes the common scripts and/or prepares the test devices. Other scripts contain examples how to do mkfs, mount, unmount, check, loop device management etc.

  2. Use the highest unused number in the sequence, write a short descriptive title and join by dashes -. This will become the directory name, eg. 012-subvolume-sync-must-wait.

  3. Write a short description of the bug and how it’s tested to the comment at the beginning of test.sh. You don’t need to add the file to git yet. Don’t forget to make the file executable, otherwise it’s not going to be executed by the infrastructure.

  4. Write the test commands, comment anything that’s not obvious.

  5. Test your test. Use the TEST variable to jump right to your test:

$ make TEST=012\* tests-misc           # from top directory
$ TEST=012\* ./misc-tests.sh           # from tests/
  1. The commit changelog should reference a commit that either introduced or fixed the bug (or both). Subject line of the shall mention the name of the new directory for ease of search, eg. btrfs-progs: tests: add 012-subvolume-sync-must-wait

  2. A commit that fixes a bug should be applied before the test that verifies the fix. This is to keep the git history bisectable.

Test images

Most tests should be able to create the test images from scratch, using regular commands and file operation. The commands also document the testcase and use the test code and kernel of the environment.

In other cases, a pre-created image may be the right way if the above does not work (eg. comparing output, requesting an exact layout or some intermediate state that would be hard to achieve otherwise).

Use xz --best and try to get the smallest size as the file is stored in git.

Crafted/fuzzed images

Images that are created by fuzzing or specially crafted to trigger some error conditions should be added to the directory fuzz-tests/images, accompanied by a textual description of the source (bugzilla, mail), the reporter, brief description of the problem or the stack trace.

If you have a fix for the problem, please submit it prior to the test image, so the fuzz tests always succeed when run on random checked out. This helps bisectability.

Exported testsuite

The tests are typically run from git on binaries built from the git sources. It is possible to extract only the testsuite files and run it independently. Use

$ make testsuite

This will gather scripts and generate tests/btrfs-progs-tests.tar.gz. The files inside the tar are in the top level directory, make sure you extract the contents to an empty directory. From there you can start the tests as described above (the non-make variant).

By default the binaries found in $PATH are used, this will normally mean the system binaries. You can also override the $TOP shell variable and this path will be used as prefix for all btrfs binaries inside the tests.

There are some utilities that are not distributed but are necessary for the tests. They are in the top level directory of the testsuite and their path cannot be set.

The tests assume write access to their directories.

Coding style, best practices


do not

Simple test template

The file tests/common provides shell functions to ease writing common things like setting up the test devices, making or mounting a filesystem, setting up loop devices.

# Simple test to create a new filesystem and test that it can be mounted

source "$TEST_TOP/common"


run_check $SUDO_HELPER dd if=/dev/zero of="$TEST_MNT"/file bs=1M count=1

Each test should be briefly described, source the helpers like run_check. The root helper is the sudo wrapper that can be used as $SUDO_HELPER variable. The implicit variables for testing device is $TEST_DEV mounted at $TEST_MNT. The mkfs and mount helpers take arguments that are then injected into the right place in the respective command.

Besides the setup and cleanup code, the main test in this example is dd that writes 1MiB to a file in the newly created filesystem.

Multiple device test template

Tests that need more devices can utilize the loop devices, an example test of the above:

# Create a new multi-device filesystem and test that it can be mounted

source "$TEST_TOP/common"

setup_loopdevs 4

run_check $SUDO_HELPER "$TOP/mkfs.btrfs" -f -d raid1 -m raid1 "${loopdevs[@]}"
run_check $SUDO_HELPER dd if=/dev/zero of="$TEST_MNT"/file bs=1M count=1


A ‘btrfs check’ test template

The easiest way to test an image is to put it to the test directory, without the test.sh script. All images found are simply processed by the shell function check_image with default parameters.

Any tweaks to the ‘check’ subcommand can be done by redefining the function:

source "$TEST_TOP/common"

check_image() {
    run_check "$TOP/btrfs" check --readonly "$1"


The images can be stored in various formats, see section ‘Test images’.

Misc hints

There are several helpers in tests/common, it’s recommended to read through that file or other tests to get the idea how easy writing a test really is.