[PATCH v2 05/18] scsi-multipath: clone each bio

[John Garry]

For failover handling, we will take the approach to resubmit each
bio.

However, unlike NVMe, for SCSI there is no guarantee that any bio submitted
is either all or none completed.

As such, for SCSI, for failover handling we will take the approach to
just re-submit the original bio. For this, clone and submit each bio.

Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
 drivers/scsi/scsi_multipath.c | 35 ++++++++++++++++++++++++++++++++++-
 include/scsi/scsi_multipath.h |  1 +
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_multipath.c b/drivers/scsi/scsi_multipath.c
index c6ae02644fdf4..068c5e93ade1e 100644
--- a/drivers/scsi/scsi_multipath.c
+++ b/drivers/scsi/scsi_multipath.c
@@ -96,6 +96,7 @@ static void scsi_mpath_head_release(struct device *dev)
 		container_of(dev, struct scsi_mpath_head, dev);
 	struct mpath_head *mpath_head = scsi_mpath_head->mpath_head;
 
+	bioset_exit(&scsi_mpath_head->bio_pool);
 	ida_free(&scsi_multipath_dev_ida, scsi_mpath_head->index);
 	mpath_put_head(mpath_head);
 	kfree(scsi_mpath_head);
@@ -230,6 +231,32 @@ static int scsi_multipath_sdev_init(struct scsi_device *sdev)
 	return 0;
 }
 
+static void scsi_mpath_clone_end_io(struct bio *clone)
+{
+	struct bio *master_bio = clone->bi_private;
+
+	master_bio->bi_status = clone->bi_status;
+	bio_put(clone);
+	bio_endio(master_bio);
+}
+
+static struct bio *scsi_mpath_clone_bio(struct bio *bio)
+{
+	struct mpath_head *mpath_head = bio->bi_bdev->bd_disk->private_data;
+	struct scsi_mpath_head *scsi_mpath_head = mpath_head->drvdata;
+	struct bio *clone;
+
+	clone = bio_alloc_clone(bio->bi_bdev, bio, GFP_NOIO,
+				&scsi_mpath_head->bio_pool);
+	if (!clone)
+		return NULL;
+
+	clone->bi_end_io = scsi_mpath_clone_end_io;
+	clone->bi_private = bio;
+
+	return clone;
+}
+
 static enum mpath_iopolicy_e scsi_mpath_get_iopolicy(struct mpath_head *mpath_head)
 {
 	struct scsi_mpath_head *scsi_mpath_head = mpath_head->drvdata;
@@ -239,6 +266,7 @@ static enum mpath_iopolicy_e scsi_mpath_get_iopolicy(struct mpath_head *mpath_he
 
 struct mpath_head_template smpdt = {
 	.get_iopolicy = scsi_mpath_get_iopolicy,
+	.clone_bio = scsi_mpath_clone_bio,
 };
 
 static struct scsi_mpath_head *scsi_mpath_alloc_head(void)
@@ -252,9 +280,12 @@ static struct scsi_mpath_head *scsi_mpath_alloc_head(void)
 
 	ida_init(&scsi_mpath_head->ida);
 
+	if (bioset_init(&scsi_mpath_head->bio_pool, BIO_POOL_SIZE,
+			0, BIOSET_PERCPU_CACHE))
+		goto out_free;
 	scsi_mpath_head->mpath_head = mpath_alloc_head();
 	if (IS_ERR(scsi_mpath_head->mpath_head))
-		goto out_free;
+		goto out_bioset_exit;
 	scsi_mpath_head->mpath_head->mpdt = &smpdt;
 	scsi_mpath_head->mpath_head->drvdata = scsi_mpath_head;
 	scsi_mpath_head->iopolicy.iopolicy = iopolicy;
@@ -279,6 +310,8 @@ static struct scsi_mpath_head *scsi_mpath_alloc_head(void)
 	ida_free(&scsi_multipath_dev_ida, scsi_mpath_head->index);
 out_put_head:
 	mpath_put_head(scsi_mpath_head->mpath_head);
+out_bioset_exit:
+	bioset_exit(&scsi_mpath_head->bio_pool);
 out_free:
 	kfree(scsi_mpath_head);
 	return NULL;
diff --git a/include/scsi/scsi_multipath.h b/include/scsi/scsi_multipath.h
index de6339989d2a2..c2eeccea52d3b 100644
--- a/include/scsi/scsi_multipath.h
+++ b/include/scsi/scsi_multipath.h
@@ -25,6 +25,7 @@ struct scsi_mpath_head {
 	struct ida		ida;
 	struct kref		ref;
 	struct mpath_iopolicy	iopolicy;
+	struct bio_set		bio_pool;
 	struct mpath_head	*mpath_head;
 	struct device		dev;
 	int			index;
-- 
2.43.5