To run these tests:

     If testing overlayfs, do:

	./run --ov

     To run the tests with nested overlayfs, do:

	./run --ovov

     To run the tests without any unioning, do:

	./run --no

     To just set up the environment and exit without doing any tests,
     add the -s flag, e.g.:

	./run --ov -s

     To run overlayfs tests with all layers on the same underlying fs,
     add the --samefs flag, e.g.:

	./run --ov --samefs

     To run overlayfs tests with lower layer on a squashfs image,
     add the --squashfs flag, e.g.:

	./run --ov --squashfs

     To run overlayfs tests with up to N middle layers, do:

	./run --ov=<N>

     The run will start with two layers and during some tests, upper layer
     will be rotated to the top of the lower layer stack and a new upper
     layer will be created.

     To run overlayfs tests with up to N middle layers, M middle layers on
     unique underlying filesystems, do:

	./run --ov=<N> --maxfs=<M>

     The first M rotations will create a new filesystem as the upper layer.

     To run the tests using a FUSE overlay file system implementation:

	./run --ov --fuse=<subfs-type>


The following environment variables are supported:

     UNIONMOUNT_BASEDIR  - parent dir of all samefs layers (default: /base)
     UNIONMOUNT_LOWERDIR - lower layer path for non samefs (default: /lower)
     UNIONMOUNT_MNTPOINT - mount point for executing tests (default: /mnt)

     When user provides UNIONMOUNT_LOWERDIR:

     1) Path should be an existing directory whose content will be deleted.
     2) Path is assumed to be on a different filesystem than base dir, so
        --samefs setup is not supported.

     When user provides UNIONMOUNT_BASEDIR:

     1) Path should be an existing directory whose content will be deleted.
     2) Upper layer and middle layers will be created under base dir.
     3) If UNIONMOUNT_MNTPOINT is not provided, the overlay mount point will
        be created under base dir.
     4) If UNIONMOUNT_LOWERDIR is not provided, the lower layer dir will be
        created under base dir.
     5) If UNIONMOUNT_LOWERDIR is not provided, the test setup defaults to
        --samefs (i.e. lower and upper layers are on the same base fs).
        However, if --maxfs=<M> is specified, a tmpfs instance will be mounted
        on the lower layer dir that was created under base dir.


For more advanced overlayfs test options and more examples, see:
     https://github.com/amir73il/overlayfs/wiki/Overlayfs-testing