block: return on congested block device
authorGoldwyn Rodrigues <rgoldwyn@suse.com>
Tue, 20 Jun 2017 12:05:46 +0000 (07:05 -0500)
committerJens Axboe <axboe@kernel.dk>
Tue, 20 Jun 2017 13:12:03 +0000 (07:12 -0600)
commit03a07c92a9ed9938d828ca7f1d11b8bc63a7bb89
treeaced260faa3cdf56d6f1140579ffaf46f8ba9c25
parenta38d1243704f501a4c42de1db1062ff6eba83453
block: return on congested block device

A new bio operation flag REQ_NOWAIT is introduced to identify bio's
orignating from iocb with IOCB_NOWAIT. This flag indicates
to return immediately if a request cannot be made instead
of retrying.

Stacked devices such as md (the ones with make_request_fn hooks)
currently are not supported because it may block for housekeeping.
For example, an md can have a part of the device suspended.
For this reason, only request based devices are supported.
In the future, this feature will be expanded to stacked devices
by teaching them how to handle the REQ_NOWAIT flags.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
block/blk-core.c
block/blk-mq.c
fs/direct-io.c
include/linux/bio.h
include/linux/blk_types.h