[PATCH block#for-2.6.31] block: add request clone interface

[Kiyoshi Ueda]

Hi Jens,

Recently, I posted an updated version of request-based dm patch-set
(http://marc.info/?l=dm-devel&m=124392590507004&w=2) which was made
on top of block#for-2.6.31.
In block#for-2.6.31, __sector and __data_len of struct request are
commented as 'internal, NEVER access directly'.
However, since request-based dm needs to copy the latest status of
the original request to clone, those fields are still accessed
directly in the request-based dm patch-set.

I'd like to solve this issue without breaking the new block-layer policy.
If those fields should not be accessed directly, I need a helper
function to copy the original request.
What do you think about the following patch which adds request cloning
interface to the block-layer?
Please apply if you have no problem.



This patch adds the following 2 interfaces for request-stacking drivers:

  - blk_rq_prep_clone(struct request *clone, struct request *orig,
		      struct bio_set *bs, gfp_t gfp_mask,
		      int (*bio_ctr)(struct bio *, struct bio*, void *),
		      void *data)
      * Clones bios in the original request to the clone request
        (bio_ctr is called for each cloned bios.)
      * Copies the clone-related information of the original request
        to the clone request.

  - blk_rq_unprep_clone(struct request *clone)
      * Frees cloned bios from the clone request.

Request stacking drivers (e.g. request-based dm) need to make a clone
request for a submitted request and dispatch it to other devices.

To allocate request for the clone, request stacking drivers may not
be able to use blk_get_request() because the allocation may be done
in an irq-disabled context.
So blk_rq_prep_clone() takes a request allocated by the caller
as an argument.

For each clone bio in the clone request, request stacking drivers
should be able to set up their own completion handler.
So blk_rq_prep_clone() takes a callback function which is called
for each clone bio, and a pointer for private data which is passed
to the callback.

Signed-off-by: Kiyoshi Ueda <k-ueda@xxxxxxxxxxxxx>
Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
---
 block/blk-core.c       |   98 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/blkdev.h |    5 ++
 2 files changed, 103 insertions(+)

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
@@ -2295,6 +2295,104 @@ int blk_lld_busy(struct request_queue *q
 }
 EXPORT_SYMBOL_GPL(blk_lld_busy);
 
+/**
+ * blk_rq_unprep_clone - Helper function to free all bios in a cloned request
+ * @rq: the clone request to be cleaned up
+ *
+ * Description:
+ *     Free all bios in @rq for a cloned request.
+ */
+void blk_rq_unprep_clone(struct request *rq)
+{
+	struct bio *bio;
+
+	while ((bio = rq->bio) != NULL) {
+		rq->bio = bio->bi_next;
+
+		bio_put(bio);
+	}
+}
+EXPORT_SYMBOL_GPL(blk_rq_unprep_clone);
+
+/*
+ * Copy request information of the original request to the clone request.
+ */
+static void __blk_rq_prep_clone(struct request *dst, struct request *src)
+{
+	dst->cpu = src->cpu;
+	dst->cmd_flags = (rq_data_dir(src) | REQ_NOMERGE);
+	dst->cmd_type = src->cmd_type;
+	dst->__sector = blk_rq_pos(src);
+	dst->__data_len = blk_rq_bytes(src);
+	dst->nr_phys_segments = src->nr_phys_segments;
+	dst->ioprio = src->ioprio;
+	dst->buffer = src->buffer;
+	dst->cmd_len = src->cmd_len;
+	dst->cmd = src->cmd;
+	dst->extra_len = src->extra_len;
+	dst->sense = src->sense;
+}
+
+/**
+ * blk_rq_prep_clone - Helper function to setup clone request
+ * @rq: the request to be setup
+ * @rq_src: original request to be cloned
+ * @bs: bio_set that bios for clone are allocated from
+ * @gfp_mask: memory allocation mask for bio
+ * @bio_ctr: setup function to be called for each clone bio.
+ *           Returns %0 for success, non %0 for failure.
+ * @data: private data to be passed to @bio_ctr
+ *
+ * Description:
+ *     Clones bios in @rq_src to @rq, and copies clone-related information
+ *     of @rq_src to @rq.
+ */
+int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
+		      struct bio_set *bs, gfp_t gfp_mask,
+		      int (*bio_ctr)(struct bio *, struct bio *, void *),
+		      void *data)
+{
+	struct bio *bio, *bio_src;
+
+	if (!bs)
+		bs = fs_bio_set;
+
+	blk_rq_init(NULL, rq);
+
+	__rq_for_each_bio(bio_src, rq_src) {
+		bio = bio_alloc_bioset(gfp_mask, bio_src->bi_max_vecs, bs);
+		if (!bio)
+			goto free_and_out;
+
+		__bio_clone(bio, bio_src);
+
+		if (bio_integrity(bio_src) &&
+		    bio_integrity_clone(bio, bio_src, gfp_mask))
+			goto free_and_out;
+
+		if (bio_ctr && bio_ctr(bio, bio_src, data))
+			goto free_and_out;
+
+		if (rq->bio) {
+			rq->biotail->bi_next = bio;
+			rq->biotail = bio;
+		} else
+			rq->bio = rq->biotail = bio;
+	}
+
+	__blk_rq_prep_clone(rq, rq_src);
+
+	return 0;
+
+free_and_out:
+	if (bio)
+		bio_free(bio, bs);
+	blk_rq_unprep_clone(rq);
+
+	return -ENOMEM;
+}
+EXPORT_SYMBOL_GPL(blk_rq_prep_clone);
+
 int kblockd_schedule_work(struct request_queue *q, struct work_struct *work)
 {
 	return queue_work(kblockd_workqueue, work);
Index: linux-2.6-block/include/linux/blkdev.h
===================================================================
--- linux-2.6-block.orig/include/linux/blkdev.h
+++ linux-2.6-block/include/linux/blkdev.h
@@ -765,6 +765,11 @@ extern void blk_insert_request(struct re
 extern void blk_requeue_request(struct request_queue *, struct request *);
 extern int blk_rq_check_limits(struct request_queue *q, struct request *rq);
 extern int blk_lld_busy(struct request_queue *q);
+extern int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
+			     struct bio_set *bs, gfp_t gfp_mask,
+			     int (*bio_ctr)(struct bio *, struct bio *, void *),
+			     void *data);
+extern void blk_rq_unprep_clone(struct request *rq);
 extern int blk_insert_cloned_request(struct request_queue *q,
 				     struct request *rq);
 extern void blk_plug_device(struct request_queue *);
--
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