| Message ID | 20171018165258.23212-4-hch@lst.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
> +/** > + * direct_make_request - hand a buffer directly to its device driver for I/O > + * @bio: The bio describing the location in memory and on the device. > + * > + * This function behaves like generic_make_request(), but does not protect > + * against recursion. Must only be used if the called driver is known > + * to not call generic_make_request (or direct_make_request) again from > + * its make_request function. (Calling direct_make_request again from > + * a workqueue is perfectly fine as that doesn't recurse). Question: are the double spaces on purpose?
>> +/** >> + * direct_make_request - hand a buffer directly to its device driver >> for I/O >> + * @bio: The bio describing the location in memory and on the device. >> + * >> + * This function behaves like generic_make_request(), but does not >> protect >> + * against recursion. Must only be used if the called driver is known >> + * to not call generic_make_request (or direct_make_request) again from >> + * its make_request function. (Calling direct_make_request again from >> + * a workqueue is perfectly fine as that doesn't recurse). > > Question: are the double spaces on purpose? Other than that, Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
On Thu, Oct 19, 2017 at 01:35:58PM +0300, Sagi Grimberg wrote: > >> +/** >> + * direct_make_request - hand a buffer directly to its device driver for I/O >> + * @bio: The bio describing the location in memory and on the device. >> + * >> + * This function behaves like generic_make_request(), but does not protect >> + * against recursion. Must only be used if the called driver is known >> + * to not call generic_make_request (or direct_make_request) again from >> + * its make_request function. (Calling direct_make_request again from >> + * a workqueue is perfectly fine as that doesn't recurse). > > Question: are the double spaces on purpose? Yes. It's a very common style, and especially useful with monospace fonts. https://en.wikipedia.org/wiki/Sentence_spacing for reference.
>>> +/** >>> + * direct_make_request - hand a buffer directly to its device driver for I/O >>> + * @bio: The bio describing the location in memory and on the device. >>> + * >>> + * This function behaves like generic_make_request(), but does not protect >>> + * against recursion. Must only be used if the called driver is known >>> + * to not call generic_make_request (or direct_make_request) again from >>> + * its make_request function. (Calling direct_make_request again from >>> + * a workqueue is perfectly fine as that doesn't recurse). >> >> Question: are the double spaces on purpose? > > Yes. It's a very common style, and especially useful with monospace fonts. > https://en.wikipedia.org/wiki/Sentence_spacing for reference. > Thanks.
diff --git a/block/blk-core.c b/block/blk-core.c index 14f7674fa0b1..b8c80f39f5fe 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -2241,6 +2241,40 @@ blk_qc_t generic_make_request(struct bio *bio) } EXPORT_SYMBOL(generic_make_request); +/** + * direct_make_request - hand a buffer directly to its device driver for I/O + * @bio: The bio describing the location in memory and on the device. + * + * This function behaves like generic_make_request(), but does not protect + * against recursion. Must only be used if the called driver is known + * to not call generic_make_request (or direct_make_request) again from + * its make_request function. (Calling direct_make_request again from + * a workqueue is perfectly fine as that doesn't recurse). + */ +blk_qc_t direct_make_request(struct bio *bio) +{ + struct request_queue *q = bio->bi_disk->queue; + bool nowait = bio->bi_opf & REQ_NOWAIT; + blk_qc_t ret; + + if (!generic_make_request_checks(bio)) + return BLK_QC_T_NONE; + + if (unlikely(blk_queue_enter(q, nowait))) { + if (nowait && !blk_queue_dying(q)) + bio->bi_status = BLK_STS_AGAIN; + else + bio->bi_status = BLK_STS_IOERR; + bio_endio(bio); + return BLK_QC_T_NONE; + } + + ret = q->make_request_fn(q, bio); + blk_queue_exit(q); + return ret; +} +EXPORT_SYMBOL_GPL(direct_make_request); + /** * submit_bio - submit a bio to the block device layer for I/O * @bio: The &struct bio which describes the I/O diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 02fa42d24b52..780f01db5899 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -936,6 +936,7 @@ do { \ extern int blk_register_queue(struct gendisk *disk); extern void blk_unregister_queue(struct gendisk *disk); extern blk_qc_t generic_make_request(struct bio *bio); +extern blk_qc_t direct_make_request(struct bio *bio); extern void blk_rq_init(struct request_queue *q, struct request *rq); extern void blk_init_request_from_bio(struct request *req, struct bio *bio); extern void blk_put_request(struct request *);
This helper allows reinserting a bio into a new queue without much overhead, but requires all queue limits to be the same for the upper and lower queues, and it does not provide any recursion preventions. Signed-off-by: Christoph Hellwig <hch@lst.de> --- block/blk-core.c | 34 ++++++++++++++++++++++++++++++++++ include/linux/blkdev.h | 1 + 2 files changed, 35 insertions(+)