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Date: Thu, 30 Apr 2009 16:46:22 +0300
From: Boaz Harrosh <bharrosh@...asas.com>
To: Tejun Heo <tj@...nel.org>
CC: axboe@...nel.dk, linux-kernel@...r.kernel.org, jeff@...zik.org,
linux-ide@...r.kernel.org, James.Bottomley@...senPartnership.com,
linux-scsi@...r.kernel.org, bzolnier@...il.com,
petkovbb@...glemail.com, sshtylyov@...mvista.com,
mike.miller@...com, chirag.kantharia@...com, Eric.Moore@....com,
stern@...land.harvard.edu, fujita.tomonori@....ntt.co.jp,
zaitcev@...hat.com, Geert.Uytterhoeven@...ycom.com,
sfr@...b.auug.org.au, grant.likely@...retlab.ca,
paul.clements@...eleye.com, jesper.juhl@...il.com,
tim@...erelk.net, jeremy@...source.com, adrian@...en.demon.co.uk,
oakad@...oo.com, dwmw2@...radead.org, schwidefsky@...ibm.com,
ballabio_dario@....com, davem@...emloft.net, rusty@...tcorp.com.au,
Markus.Lidel@...dowconnect.com
Subject: Re: [PATCH 07/10] block: drop request->hard_* and *nr_sectors
On 04/29/2009 12:13 PM, Tejun Heo wrote:
> struct request has had a few different ways to represent some
> properties of a request. ->hard_* represent block layer's view of the
> request progress (completion cursor) and the ones without the prefix
> are supposed to represent the issue cursor and allowed to be updated
> as necessary by the low level drivers. The thing is that as block
> layer supports partial completion, the two cursors really aren't
> necessary and only cause confusion. In addition, manual management of
> request detail from low level drivers is cumbersome and error-prone at
> the very least.
>
> Another interesting duplicate fields are rq->[hard_]nr_sectors and
> rq->{hard_cur|current}_nr_sectors against rq->data_len and
> rq->bio->bi_size. This is more convoluted than the hard_ case.
>
> rq->[hard_]nr_sectors are initialized for requests with bio but
> blk_rq_bytes() uses it only for !pc requests. rq->data_len is
> initialized for all request but blk_rq_bytes() uses it only for pc
> requests. This causes good amount of confusion throughout block layer
> and its drivers and determining the request length has been a bit of
> black magic which may or may not work depending on circumstances and
> what the specific LLD is actually doing.
>
> rq->{hard_cur|current}_nr_sectors represent the number of sectors in
> the contiguous data area at the front. This is mainly used by drivers
> which transfers data by walking request segment-by-segment. This
> value always equals rq->bio->bi_size >> 9. However, data length for
> pc requests may not be multiple of 512 bytes and using this field
> becomes a bit confusing.
>
> In general, having multiple fields to represent the same property
> leads only to confusion and subtle bugs. With recent block low level
> driver cleanups, no driver is accessing or manipulating these
> duplicate fields directly. Drop all the duplicates. Now rq->sector
> means the current sector, rq->data_len the current total length and
> rq->bio->bi_size the current segment length. Everything else is
> defined in terms of these three and available only through accessors.
>
> * blk_recalc_rq_sectors() is collapsed into blk_update_request() and
> now handles pc and fs requests equally other than rq->sector update.
> This means that now pc requests can use partial completion too (no
> in-kernel user yet tho).
>
> * bio_cur_sectors() is replaced with bio_cur_bytes() as block layer
> now uses byte count as the primary data length.
>
> * blk_rq_pos() is now guranteed to be always correct. In-block users
> converted.
>
> * blk_rq_bytes() is now guaranteed to be always valid as is
> blk_rq_sectors(). In-block users converted.
>
> * blk_rq_sectors() is now guaranteed to equal blk_rq_bytes() >> 9.
> More convenient one is used.
>
> [ Impact: API cleanup, single way to represent one property of a request ]
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Boaz Harrosh <bharrosh@...asas.com>
> ---
> block/blk-core.c | 81 +++++++++++++++++-----------------------------
> block/blk-merge.c | 36 ++------------------
> block/blk.h | 1 -
> block/cfq-iosched.c | 10 +++---
> include/linux/bio.h | 6 ++--
> include/linux/blkdev.h | 37 +++++++++------------
> include/linux/elevator.h | 2 +-
> kernel/trace/blktrace.c | 16 ++++----
> 8 files changed, 67 insertions(+), 122 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 82dc206..3596ca7 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -127,7 +127,7 @@ void blk_rq_init(struct request_queue *q, struct request *rq)
> INIT_LIST_HEAD(&rq->timeout_list);
> rq->cpu = -1;
> rq->q = q;
> - rq->sector = rq->hard_sector = (sector_t) -1;
> + rq->sector = (sector_t) -1;
> INIT_HLIST_NODE(&rq->hash);
> RB_CLEAR_NODE(&rq->rb_node);
> rq->cmd = rq->__cmd;
> @@ -189,8 +189,7 @@ void blk_dump_rq_flags(struct request *rq, char *msg)
> (unsigned long long)blk_rq_pos(rq),
> blk_rq_sectors(rq), blk_rq_cur_sectors(rq));
> printk(KERN_INFO " bio %p, biotail %p, buffer %p, len %u\n",
> - rq->bio, rq->biotail,
> - rq->buffer, rq->data_len);
> + rq->bio, rq->biotail, rq->buffer, blk_rq_bytes(rq));
>
> if (blk_pc_request(rq)) {
> printk(KERN_INFO " cdb: ");
> @@ -1096,7 +1095,7 @@ void init_request_from_bio(struct request *req, struct bio *bio)
> req->cmd_flags |= REQ_NOIDLE;
>
> req->errors = 0;
> - req->hard_sector = req->sector = bio->bi_sector;
> + req->sector = bio->bi_sector;
> req->ioprio = bio_prio(bio);
> blk_rq_bio_prep(req->q, req, bio);
> }
> @@ -1113,14 +1112,13 @@ static inline bool queue_should_plug(struct request_queue *q)
> static int __make_request(struct request_queue *q, struct bio *bio)
> {
> struct request *req;
> - int el_ret, nr_sectors;
> + int el_ret;
> + unsigned int bytes = bio->bi_size;
> const unsigned short prio = bio_prio(bio);
> const int sync = bio_sync(bio);
> const int unplug = bio_unplug(bio);
> int rw_flags;
>
> - nr_sectors = bio_sectors(bio);
> -
> /*
> * low level driver can indicate that it wants pages above a
> * certain limit bounced to low memory (ie for highmem, or even
> @@ -1145,7 +1143,7 @@ static int __make_request(struct request_queue *q, struct bio *bio)
>
> req->biotail->bi_next = bio;
> req->biotail = bio;
> - req->nr_sectors = req->hard_nr_sectors += nr_sectors;
> + req->data_len += bytes;
> req->ioprio = ioprio_best(req->ioprio, prio);
> if (!blk_rq_cpu_valid(req))
> req->cpu = bio->bi_comp_cpu;
> @@ -1171,10 +1169,8 @@ static int __make_request(struct request_queue *q, struct bio *bio)
> * not touch req->buffer either...
> */
> req->buffer = bio_data(bio);
> - req->current_nr_sectors = bio_cur_sectors(bio);
> - req->hard_cur_sectors = req->current_nr_sectors;
> - req->sector = req->hard_sector = bio->bi_sector;
> - req->nr_sectors = req->hard_nr_sectors += nr_sectors;
> + req->sector = bio->bi_sector;
> + req->data_len += bytes;
> req->ioprio = ioprio_best(req->ioprio, prio);
> if (!blk_rq_cpu_valid(req))
> req->cpu = bio->bi_comp_cpu;
> @@ -1557,7 +1553,7 @@ EXPORT_SYMBOL(submit_bio);
> int blk_rq_check_limits(struct request_queue *q, struct request *rq)
> {
> if (blk_rq_sectors(rq) > q->max_sectors ||
> - rq->data_len > q->max_hw_sectors << 9) {
> + blk_rq_bytes(rq) > q->max_hw_sectors << 9) {
> printk(KERN_ERR "%s: over max size limit.\n", __func__);
> return -EIO;
> }
> @@ -1675,35 +1671,6 @@ static void blk_account_io_done(struct request *req)
> }
> }
>
> -/**
> - * blk_rq_bytes - Returns bytes left to complete in the entire request
> - * @rq: the request being processed
> - **/
> -unsigned int blk_rq_bytes(struct request *rq)
> -{
> - if (blk_fs_request(rq))
> - return blk_rq_sectors(rq) << 9;
> -
> - return rq->data_len;
> -}
> -EXPORT_SYMBOL_GPL(blk_rq_bytes);
> -
> -/**
> - * blk_rq_cur_bytes - Returns bytes left to complete in the current segment
> - * @rq: the request being processed
> - **/
> -unsigned int blk_rq_cur_bytes(struct request *rq)
> -{
> - if (blk_fs_request(rq))
> - return rq->current_nr_sectors << 9;
> -
> - if (rq->bio)
> - return rq->bio->bi_size;
> -
> - return rq->data_len;
> -}
> -EXPORT_SYMBOL_GPL(blk_rq_cur_bytes);
> -
> struct request *elv_next_request(struct request_queue *q)
> {
> struct request *rq;
> @@ -1736,7 +1703,7 @@ struct request *elv_next_request(struct request_queue *q)
> if (rq->cmd_flags & REQ_DONTPREP)
> break;
>
> - if (q->dma_drain_size && rq->data_len) {
> + if (q->dma_drain_size && blk_rq_bytes(rq)) {
> /*
> * make sure space for the drain appears we
> * know we can do this because max_hw_segments
> @@ -1759,7 +1726,7 @@ struct request *elv_next_request(struct request_queue *q)
> * avoid resource deadlock. REQ_STARTED will
> * prevent other fs requests from passing this one.
> */
> - if (q->dma_drain_size && rq->data_len &&
> + if (q->dma_drain_size && blk_rq_bytes(rq) &&
> !(rq->cmd_flags & REQ_DONTPREP)) {
> /*
> * remove the space for the drain we added
> @@ -1911,8 +1878,7 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
> * can find how many bytes remain in the request
> * later.
> */
> - req->nr_sectors = req->hard_nr_sectors = 0;
> - req->current_nr_sectors = req->hard_cur_sectors = 0;
> + req->data_len = 0;
> return false;
> }
>
> @@ -1926,8 +1892,25 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
> bio_iovec(bio)->bv_len -= nr_bytes;
> }
>
> - blk_recalc_rq_sectors(req, total_bytes >> 9);
> + req->data_len -= total_bytes;
> + req->buffer = bio_data(req->bio);
> +
> + /* update sector only for requests with clear definition of sector */
> + if (blk_fs_request(req) || blk_discard_rq(req))
> + req->sector += total_bytes >> 9;
> +
> + /*
> + * If total number of sectors is less than the first segment
> + * size, something has gone terribly wrong.
> + */
> + if (blk_rq_bytes(req) < blk_rq_cur_bytes(req)) {
> + printk(KERN_ERR "blk: request botched\n");
> + req->data_len = blk_rq_cur_bytes(req);
> + }
What happens in the last bio/segment? Is it not allowed with block_pc commands
that blk_rq_bytes(req) (was data_len) be smaller then sum_bytes(bio-chain)?
Also I never understood the drain is it not appended to the last bio? I thought it
is costumery in the Kernel to allow mapping longer then actual length?
Maybe you would want blk_rq_cur_bytes(req) to return the minimum of the two, and let
bio's be longer then bytes requested. (ie. reverse above logic)
> +
> + /* recalculate the number of segments */
> blk_recalc_rq_segments(req);
> +
> return true;
> }
> EXPORT_SYMBOL_GPL(blk_update_request);
> @@ -2049,11 +2032,7 @@ void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
> rq->nr_phys_segments = bio_phys_segments(q, bio);
> rq->buffer = bio_data(bio);
> }
> - rq->current_nr_sectors = bio_cur_sectors(bio);
> - rq->hard_cur_sectors = rq->current_nr_sectors;
> - rq->hard_nr_sectors = rq->nr_sectors = bio_sectors(bio);
> rq->data_len = bio->bi_size;
> -
> rq->bio = rq->biotail = bio;
>
> if (bio->bi_bdev)
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index bf62a87..b8df66a 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -9,35 +9,6 @@
>
> #include "blk.h"
>
> -void blk_recalc_rq_sectors(struct request *rq, int nsect)
> -{
> - if (blk_fs_request(rq) || blk_discard_rq(rq)) {
> - rq->hard_sector += nsect;
> - rq->hard_nr_sectors -= nsect;
> -
> - /*
> - * Move the I/O submission pointers ahead if required.
> - */
> - if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
> - (rq->sector <= rq->hard_sector)) {
> - rq->sector = rq->hard_sector;
> - rq->nr_sectors = rq->hard_nr_sectors;
> - rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
> - rq->current_nr_sectors = rq->hard_cur_sectors;
> - rq->buffer = bio_data(rq->bio);
> - }
> -
> - /*
> - * if total number of sectors is less than the first segment
> - * size, something has gone terribly wrong
> - */
> - if (rq->nr_sectors < rq->current_nr_sectors) {
> - printk(KERN_ERR "blk: request botched\n");
> - rq->nr_sectors = rq->current_nr_sectors;
> - }
> - }
> -}
> -
> static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
> struct bio *bio)
> {
> @@ -199,8 +170,9 @@ new_segment:
>
>
> if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
> - (rq->data_len & q->dma_pad_mask)) {
> - unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1;
> + (blk_rq_bytes(rq) & q->dma_pad_mask)) {
> + unsigned int pad_len =
> + (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
>
> sg->length += pad_len;
> rq->extra_len += pad_len;
> @@ -398,7 +370,7 @@ static int attempt_merge(struct request_queue *q, struct request *req,
> req->biotail->bi_next = next->bio;
> req->biotail = next->biotail;
>
> - req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
> + req->data_len += blk_rq_bytes(next);
>
> elv_merge_requests(q, req, next);
>
> diff --git a/block/blk.h b/block/blk.h
> index 5111559..ab54529 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -101,7 +101,6 @@ int ll_front_merge_fn(struct request_queue *q, struct request *req,
> int attempt_back_merge(struct request_queue *q, struct request *rq);
> int attempt_front_merge(struct request_queue *q, struct request *rq);
> void blk_recalc_rq_segments(struct request *rq);
> -void blk_recalc_rq_sectors(struct request *rq, int nsect);
>
> void blk_queue_congestion_threshold(struct request_queue *q);
>
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index db4d990..99ac430 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -579,9 +579,9 @@ cfq_prio_tree_lookup(struct cfq_data *cfqd, struct rb_root *root,
> * Sort strictly based on sector. Smallest to the left,
> * largest to the right.
> */
> - if (sector > cfqq->next_rq->sector)
> + if (sector > blk_rq_pos(cfqq->next_rq))
> n = &(*p)->rb_right;
> - else if (sector < cfqq->next_rq->sector)
> + else if (sector < blk_rq_pos(cfqq->next_rq))
> n = &(*p)->rb_left;
> else
> break;
> @@ -611,8 +611,8 @@ static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
> return;
>
> cfqq->p_root = &cfqd->prio_trees[cfqq->org_ioprio];
> - __cfqq = cfq_prio_tree_lookup(cfqd, cfqq->p_root, cfqq->next_rq->sector,
> - &parent, &p);
> + __cfqq = cfq_prio_tree_lookup(cfqd, cfqq->p_root,
> + blk_rq_pos(cfqq->next_rq), &parent, &p);
> if (!__cfqq) {
> rb_link_node(&cfqq->p_node, parent, p);
> rb_insert_color(&cfqq->p_node, cfqq->p_root);
> @@ -996,7 +996,7 @@ static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
> if (cfq_rq_close(cfqd, __cfqq->next_rq))
> return __cfqq;
>
> - if (__cfqq->next_rq->sector < sector)
> + if (blk_rq_pos(__cfqq->next_rq) < sector)
> node = rb_next(&__cfqq->p_node);
> else
> node = rb_prev(&__cfqq->p_node);
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index f37ca8c..d30ec6f 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -218,12 +218,12 @@ struct bio {
> #define bio_sectors(bio) ((bio)->bi_size >> 9)
> #define bio_empty_barrier(bio) (bio_barrier(bio) && !bio_has_data(bio) && !bio_discard(bio))
>
> -static inline unsigned int bio_cur_sectors(struct bio *bio)
> +static inline unsigned int bio_cur_bytes(struct bio *bio)
> {
> if (bio->bi_vcnt)
> - return bio_iovec(bio)->bv_len >> 9;
> + return bio_iovec(bio)->bv_len;
> else /* dataless requests such as discard */
> - return bio->bi_size >> 9;
> + return bio->bi_size;
> }
>
> static inline void *bio_data(struct bio *bio)
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 1e18ef7..943cbfe 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -166,19 +166,8 @@ struct request {
> enum rq_cmd_type_bits cmd_type;
> unsigned long atomic_flags;
>
> - /* Maintain bio traversal state for part by part I/O submission.
> - * hard_* are block layer internals, no driver should touch them!
> - */
> -
> - sector_t sector; /* next sector to submit */
> - sector_t hard_sector; /* next sector to complete */
> - unsigned long nr_sectors; /* no. of sectors left to submit */
> - unsigned long hard_nr_sectors; /* no. of sectors left to complete */
> - /* no. of sectors left to submit in the current segment */
> - unsigned int current_nr_sectors;
> -
> - /* no. of sectors left to complete in the current segment */
> - unsigned int hard_cur_sectors;
> + sector_t sector; /* sector cursor */
> + unsigned int data_len; /* total data len, don't access directly */
>
> struct bio *bio;
> struct bio *biotail;
> @@ -226,7 +215,6 @@ struct request {
> unsigned char __cmd[BLK_MAX_CDB];
> unsigned char *cmd;
>
> - unsigned int data_len;
> unsigned int extra_len; /* length of alignment and padding */
> unsigned int sense_len;
> unsigned int resid_len; /* residual count */
> @@ -840,20 +828,27 @@ extern void blkdev_dequeue_request(struct request *req);
> */
> static inline sector_t blk_rq_pos(struct request *rq)
> {
> - return rq->hard_sector;
> + return rq->sector;
> +}
> +
> +static inline unsigned int blk_rq_bytes(struct request *rq)
> +{
> + return rq->data_len;
> }
>
> -extern unsigned int blk_rq_bytes(struct request *rq);
> -extern unsigned int blk_rq_cur_bytes(struct request *rq);
> +static inline int blk_rq_cur_bytes(struct request *rq)
> +{
> + return rq->bio ? bio_cur_bytes(rq->bio) : 0;
> +}
>
> static inline unsigned int blk_rq_sectors(struct request *rq)
> {
> - return rq->hard_nr_sectors;
> + return blk_rq_bytes(rq) >> 9;
> }
>
> static inline unsigned int blk_rq_cur_sectors(struct request *rq)
> {
> - return rq->hard_cur_sectors;
> + return blk_rq_cur_bytes(rq) >> 9;
> }
>
> /*
> @@ -928,7 +923,7 @@ static inline void blk_end_request_all(struct request *rq, int error)
> */
> static inline bool blk_end_request_cur(struct request *rq, int error)
> {
> - return blk_end_request(rq, error, rq->hard_cur_sectors << 9);
> + return blk_end_request(rq, error, blk_rq_cur_bytes(rq));
> }
>
> /**
> @@ -981,7 +976,7 @@ static inline void __blk_end_request_all(struct request *rq, int error)
> */
> static inline bool __blk_end_request_cur(struct request *rq, int error)
> {
> - return __blk_end_request(rq, error, rq->hard_cur_sectors << 9);
> + return __blk_end_request(rq, error, blk_rq_cur_bytes(rq));
> }
>
> extern void blk_complete_request(struct request *);
> diff --git a/include/linux/elevator.h b/include/linux/elevator.h
> index c59b769..4e46287 100644
> --- a/include/linux/elevator.h
> +++ b/include/linux/elevator.h
> @@ -171,7 +171,7 @@ enum {
> ELV_MQUEUE_MUST,
> };
>
> -#define rq_end_sector(rq) ((rq)->sector + (rq)->nr_sectors)
> +#define rq_end_sector(rq) (blk_rq_pos(rq) + blk_rq_sectors(rq))
> #define rb_entry_rq(node) rb_entry((node), struct request, rb_node)
>
> /*
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index 42f1c11..5708a14 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -642,12 +642,12 @@ static void blk_add_trace_rq(struct request_queue *q, struct request *rq,
>
> if (blk_pc_request(rq)) {
> what |= BLK_TC_ACT(BLK_TC_PC);
> - __blk_add_trace(bt, 0, rq->data_len, rw, what, rq->errors,
> - rq->cmd_len, rq->cmd);
> + __blk_add_trace(bt, 0, blk_rq_bytes(rq), rw,
> + what, rq->errors, rq->cmd_len, rq->cmd);
> } else {
> what |= BLK_TC_ACT(BLK_TC_FS);
> - __blk_add_trace(bt, blk_rq_pos(rq), blk_rq_sectors(rq) << 9,
> - rw, what, rq->errors, 0, NULL);
> + __blk_add_trace(bt, blk_rq_pos(rq), blk_rq_bytes(rq), rw,
> + what, rq->errors, 0, NULL);
> }
> }
>
> @@ -854,11 +854,11 @@ void blk_add_driver_data(struct request_queue *q,
> return;
>
> if (blk_pc_request(rq))
> - __blk_add_trace(bt, 0, rq->data_len, 0, BLK_TA_DRV_DATA,
> - rq->errors, len, data);
> + __blk_add_trace(bt, 0, blk_rq_bytes(rq), 0,
> + BLK_TA_DRV_DATA, rq->errors, len, data);
> else
> - __blk_add_trace(bt, blk_rq_pos(rq), blk_rq_sectors(rq) << 9,
> - 0, BLK_TA_DRV_DATA, rq->errors, len, data);
> + __blk_add_trace(bt, blk_rq_pos(rq), blk_rq_bytes(rq), 0,
> + BLK_TA_DRV_DATA, rq->errors, len, data);
> }
> EXPORT_SYMBOL_GPL(blk_add_driver_data);
>
Thanks, very^3 nice stuff
Boaz
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