block: enable passthrough command statistics

block: enable passthrough command statistics

Applications using the passthrough interfaces for IO want to continue
seeing the disk stats. These requests had been fenced off from this
block layer feature. While the block layer doesn't necessarily know what
a passthrough command does, we do know the data size and direction,
which is enough to account for the command's stats.

Since tracking these has the potential to produce unexpected results,
the passthrough stats are locked behind a new queue flag that needs to
be enabled with the /sys/block/<dev>/queue/iostats_passthrough
attribute.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20241007153236.2818562-1-kbusch@meta.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>