[PATCH v9 16/29] 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.garry at linux.dev>
---
 drivers/scsi/scsi_multipath.c | 33 +++++++++++++++++++++++++++++++++
 include/scsi/scsi_multipath.h |  1 +
 2 files changed, 34 insertions(+)

diff --git a/drivers/scsi/scsi_multipath.c b/drivers/scsi/scsi_multipath.c
index baf4ca73f8c9..8e229357e62c 100644
--- a/drivers/scsi/scsi_multipath.c
+++ b/drivers/scsi/scsi_multipath.c
@@ -101,6 +101,7 @@ 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);
 	ida_destroy(&scsi_mpath_head->ida);
 	mpath_head_uninit(mpath_head);
@@ -239,7 +240,34 @@ 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 = to_scsi_mpath_head(mpath_head);
+	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 struct mpath_head_template smpdt = {
+	.clone_bio = scsi_mpath_clone_bio,
 };
 
 static struct scsi_mpath_head *scsi_mpath_alloc_head(char *vpd_id)
@@ -265,6 +293,9 @@ static struct scsi_mpath_head *scsi_mpath_alloc_head(char *vpd_id)
 	scsi_mpath_head->index = ida_alloc(&scsi_multipath_dev_ida, GFP_KERNEL);
 	if (scsi_mpath_head->index < 0)
 		goto out_uninit_head;
+	if (bioset_init(&scsi_mpath_head->bio_pool, BIO_POOL_SIZE,
+			0, BIOSET_PERCPU_CACHE))
+		goto out_ida_free;
 	kref_init(&scsi_mpath_head->ref);
 
 	device_initialize(&scsi_mpath_head->dev);
@@ -284,6 +315,8 @@ static struct scsi_mpath_head *scsi_mpath_alloc_head(char *vpd_id)
 
 	return scsi_mpath_head;
 
+out_ida_free:
+	ida_free(&scsi_multipath_dev_ida, scsi_mpath_head->index);
 out_uninit_head:
 	mpath_head_uninit(&scsi_mpath_head->mpath_head);
 out_free:
diff --git a/include/scsi/scsi_multipath.h b/include/scsi/scsi_multipath.h
index d6f290b84f7f..d2ef94ebd29a 100644
--- a/include/scsi/scsi_multipath.h
+++ b/include/scsi/scsi_multipath.h
@@ -26,6 +26,7 @@ struct scsi_mpath_head {
 	struct ida		ida;
 	struct kref		ref;
 	enum mpath_iopolicy_e	iopolicy;
+	struct bio_set		bio_pool;
 	struct device		dev;
 	int			index;
 };
-- 
2.43.0