[dm-devel] Re: [PATCH 02/13] block: add request submission interface
Kiyoshi Ueda
k-ueda at ct.jp.nec.com
Tue Sep 16 16:06:56 UTC 2008
Hi Boaz, Jens,
On Sun, 14 Sep 2008 16:10:58 +0300, Boaz Harrosh wrote:
> Kiyoshi Ueda wrote:
> > This patch adds blk_submit_request(), a generic request submission
> > interface for request stacking drivers.
> > Request-based dm will use it to submit their clones to underlying
> > devices.
> >
> > blk_rq_check_limits() is also added because it is possible that
> > the lower queue has stronger limitations than the upper queue
> > if multiple drivers are stacking at request-level.
> > Not only for blk_submit_request()'s internal use, the function
> > will be used by request-based dm when the queue limitation is
> > modified (e.g. by replacing dm's table).
> >
> >
> > Signed-off-by: Kiyoshi Ueda <k-ueda at ct.jp.nec.com>
> > Signed-off-by: Jun'ichi Nomura <j-nomura at ce.jp.nec.com>
> > Cc: Jens Axboe <jens.axboe at oracle.com>
> > ---
> > block/blk-core.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++++
> > include/linux/blkdev.h | 2 +
> > 2 files changed, 83 insertions(+)
> >
> > Index: 2.6.27-rc6/block/blk-core.c
> > ===================================================================
> > --- 2.6.27-rc6.orig/block/blk-core.c
> > +++ 2.6.27-rc6/block/blk-core.c
> > @@ -1517,6 +1517,87 @@ void submit_bio(int rw, struct bio *bio)
> > EXPORT_SYMBOL(submit_bio);
> >
> > /**
> > + * blk_rq_check_limits - Helper function to check a request for the queue limit
> > + * @q: the queue
> > + * @rq: the request being checked
> > + *
> > + * Description:
> > + * @rq may have been made based on weaker limitations of upper-level queues
> > + * in request stacking drivers, and it may violate the limitation of @q.
> > + * Since the block layer and the underlying device driver trust @rq
> > + * after it is inserted to @q, it should be checked against @q before
> > + * the insertion using this generic function.
> > + *
> > + * This function should also be useful for request stacking drivers
> > + * in some cases below, so export this fuction.
> > + * Request stacking drivers like request-based dm may change the queue
> > + * limits while requests are in the queue (e.g. dm's table swapping).
> > + * Such request stacking drivers should check those requests agaist
> > + * the new queue limits again when they dispatch those requests,
> > + * although such checkings are also done against the old queue limits
> > + * when submitting requests.
> > + */
> > +int blk_rq_check_limits(struct request_queue *q, struct request *rq)
> > +{
> > + if (rq->nr_sectors > q->max_sectors ||
> > + rq->data_len > q->max_hw_sectors << 9) {
> > + printk(KERN_ERR "%s: over max size limit.\n", __func__);
> > + return -EIO;
> > + }
> > +
> > + /*
> > + * queue's settings related to segment counting like q->bounce_pfn
> > + * may differ from that of other stacking queues.
> > + * Recalculate it to check the request correctly on this queue's
> > + * limitation.
> > + */
> > + blk_recalc_rq_segments(rq);
> > + if (rq->nr_phys_segments > q->max_phys_segments ||
> > + rq->nr_hw_segments > q->max_hw_segments) {
> > + printk(KERN_ERR "%s: over max segments limit.\n", __func__);
> > + return -EIO;
> > + }
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(blk_rq_check_limits);
> > +
> > +/**
> > + * blk_submit_request - Helper for stacking drivers to submit a request
> > + * @q: the queue to submit the request
> > + * @rq: the request being queued
> > + */
> > +int blk_submit_request(struct request_queue *q, struct request *rq)
> > +{
> > + unsigned long flags;
> > +
> > + if (blk_rq_check_limits(q, rq))
> > + return -EIO;
> > +
> > +#ifdef CONFIG_FAIL_MAKE_REQUEST
> > + if (rq->rq_disk && rq->rq_disk->flags & GENHD_FL_FAIL &&
> > + should_fail(&fail_make_request, blk_rq_bytes(rq)))
> > + return -EIO;
> > +#endif
> > +
> > + spin_lock_irqsave(q->queue_lock, flags);
> > +
> > + /*
> > + * Submitting request must be dequeued before calling this function
> > + * because it will be linked to another request_queue
> > + */
> > + BUG_ON(blk_queued_rq(rq));
> > +
> > + drive_stat_acct(rq, 1);
> > + __elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 0);
> > +
> > + spin_unlock_irqrestore(q->queue_lock, flags);
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(blk_submit_request);
> > +
>
> This looks awfully similar to blk_execute_rq_nowait With an Added
> blk_rq_check_limits, minus the __generic_unplug_device() and
> q->request_fn(q) calls. Perhaps the common code could be re factored
> out?
They might look simlar but don't have much in common actually.
I could refactor them like the attached patch, but I'm not sure
this is a correct way and this is cleaner than the current code.
(e.g. blk_execute_rq_nowait() can't be called with irqs-disabled,
but blk_insert_request() and my blk_submit_request() can be called
with irqs-disabled.)
So I'd leave them as it is unless you or others strongly prefer
the attached patch...
Anyway, I would like to leave the refactoring as a separate patch,
since it's not so straightforward.
> Also isn't block-exec.c a better file for this function?
blk_insert_request() is in blk-core.c and it is similar to
blk_submit_request(), so I added it to blk-core.c.
But maybe both should be in blk-exec.c.
I don't have any problem on this, I'd like to hear Jens' opinion.
Thanks,
Kiyoshi Ueda
---
block/blk-core.c | 20 +++----------------
block/blk-exec.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++-------
2 files changed, 54 insertions(+), 23 deletions(-)
Index: linux-2.6-block/block/blk-core.c
===================================================================
--- linux-2.6-block.orig/block/blk-core.c
+++ linux-2.6-block/block/blk-core.c
@@ -881,7 +881,7 @@ EXPORT_SYMBOL(blk_get_request);
*/
void blk_start_queueing(struct request_queue *q)
{
- if (!blk_queue_plugged(q))
+ if (!blk_queue_plugged(q) && !blk_queue_stopped(q))
q->request_fn(q);
else
__generic_unplug_device(q);
@@ -930,11 +930,10 @@ EXPORT_SYMBOL(blk_requeue_request);
* of the queue for things like a QUEUE_FULL message from a device, or a
* host that is unable to accept a particular command.
*/
-void blk_insert_request(struct request_queue *q, struct request *rq,
- int at_head, void *data)
+void blk_insert_special_request(struct request_queue *q, struct request *rq,
+ int at_head, void *data)
{
int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
- unsigned long flags;
/*
* tell I/O scheduler that this isn't a regular read/write (ie it
@@ -946,18 +945,7 @@ void blk_insert_request(struct request_q
rq->special = data;
- spin_lock_irqsave(q->queue_lock, flags);
-
- /*
- * If command is tagged, release the tag
- */
- if (blk_rq_tagged(rq))
- blk_queue_end_tag(q, rq);
-
- drive_stat_acct(rq, 1);
- __elv_add_request(q, rq, where, 0);
- blk_start_queueing(q);
- spin_unlock_irqrestore(q->queue_lock, flags);
+ blk_insert_request(q, rq, where, 1);
}
EXPORT_SYMBOL(blk_insert_request);
Index: linux-2.6-block/block/blk-exec.c
===================================================================
--- linux-2.6-block.orig/block/blk-exec.c
+++ linux-2.6-block/block/blk-exec.c
@@ -33,6 +33,46 @@ static void blk_end_sync_rq(struct reque
}
/**
+ * blk_insert_request - Helper function for inserting a request
+ * @q: request queue where request should be inserted
+ * @rq: request to be inserted
+ * @where: where insert request to
+ * @run_queue: run the queue or not
+ */
+static void blk_insert_request(struct request_queue *q, struct request *rq,
+ int where, int run_queue)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(q->queue_lock, flags);
+
+ /*
+ * Submitting request must be dequeued before calling this function
+ * because it will be linked to another request_queue
+ */
+ BUG_ON(blk_queued_rq(rq));
+
+ /*
+ * If command is tagged, release the tag
+ */
+ if (blk_rq_tagged(rq))
+ blk_queue_end_tag(q, rq);
+
+ drive_stat_acct(rq, 1);
+ __elv_add_request(q, rq, where, 0);
+
+ if (run_queue) {
+ blk_start_queueing(q);
+
+ /* the queue is stopped so it won't be plugged+unplugged */
+ if (blk_pm_resume_request(rq))
+ q->request_fn(q);
+ }
+
+ spin_unlock_irqrestore(q->queue_lock, flags);
+}
+
+/**
* blk_execute_rq_nowait - insert a request into queue for execution
* @q: queue to insert the request in
* @bd_disk: matching gendisk
@@ -54,13 +94,7 @@ void blk_execute_rq_nowait(struct reques
rq->cmd_flags |= REQ_NOMERGE;
rq->end_io = done;
WARN_ON(irqs_disabled());
- spin_lock_irq(q->queue_lock);
- __elv_add_request(q, rq, where, 1);
- __generic_unplug_device(q);
- /* the queue is stopped so it won't be plugged+unplugged */
- if (blk_pm_resume_request(rq))
- q->request_fn(q);
- spin_unlock_irq(q->queue_lock);
+ blk_insert_request(q, rq, where, 1);
}
EXPORT_SYMBOL_GPL(blk_execute_rq_nowait);
@@ -104,3 +138,12 @@ int blk_execute_rq(struct request_queue
return err;
}
EXPORT_SYMBOL(blk_execute_rq);
+
+int blk_insert_clone_request(struct request_queue *q, struct request *rq)
+{
+ if (blk_rq_check_limits(q, rq))
+ return -EIO;
+
+ blk_insert_request(q, rq, ELEVATOR_INSERT_BACK, 0);
+}
+EXPORT_SYMBOL_GPL(blk_insert_clone_request);
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