Comment 7 for bug 1829563

Tests with I/O errors
=====================

The I/O error tests in the caching and backing device have been
simulated with the device mapper dm-linear and dm-error targets.

The tests are based on the patch messages, which describe a
problem and/or expected behavior, so to exercise the change.

Comparisons/comments between the original & modified/test kernels
are provided in the next comments.

The test script initially sets up fake DM devices in 'good' state
with the linear target, and later can switch them to 'bad' state
with the error target, and back again.
(attached script: 'dm_fake_dev.sh')

The bcache setup uses the DM devices above (for caching and backing
devices) on top of loop devices in a virtual machine for flexibility.
(attached script: 'setup.sh')

One test uses a scsi-debug SCSI disk as backing device to offline it.
(attached script: 'setup-sda.sh')

One test uses 2 bcache devices with 1 shared cache device to ensure
only one bcache device is stopped if 1 backing device has failures.
(attached script: 'setup-two-bcache-one-cache.sh')