Commits
Shaohua Li committed deb78b419df
nullb: emulate cache Software must flush disk cache to guarantee data safety. To check if software correctly does disk cache flush, we must know the behavior of disk. But physical disk behavior is uncontrollable. Even software doesn't do the flush, the disk probably does the flush. This patch tries to emulate a cache in the test disk. All write will go to a cache first, when the cache is full, we then flush some data to disk storage. A flush request will flush all data of the cache to disk storage. A FUA write will write to memory store directly and revalidate data in cache. If there is a power failure (by writing to power attribute, 'echo 0 > disk_name/power'), we discard all data in the cache, but preserve the data in disk storage. Later we can power on the disk again as usual (write 1 to 'power' attribute), then we can check data integrity and very if software does everything correctly. A new attribute 'cache_size' (in MB) is added to configure cache size. Based on original patch from Kyungchan Koh Signed-off-by: Kyungchan Koh <kkc6196@fb.com> Signed-off-by: Shaohua Li <shli@fb.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>