block: introduce part_[begin|end]_io_acct

These functions can be used to enable iostat for partitions on devices
like md, bcache.

Signed-off-by: Song Liu <songliubraving@fb.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2 files changed