cachefiles: Add error injection support

Add support for injecting ENOSPC or EIO errors.  This needs to be enabled
by CONFIG_CACHEFILES_ERROR_INJECTION=y.  Once enabled, ENOSPC on things
like write and mkdir can be triggered by:

	echo 1 >/proc/sys/cachefiles/error_injection

and EIO can be triggered on most operations by:

	echo 2 >/proc/sys/cachefiles/error_injection

Signed-off-by: David Howells <dhowells@redhat.com>
9 files changed