[Devel] [PATCH RH9 v3 2/8] dm: add llseek_hole infrastructure

[Andrey Zhadchenko]

Add new function to target_type, so any dm devices may realize it
Implement intermediate llseek_hole() on device-mapper layer, do some simple
checks.

Feature: dm: implement SEEK_HOLE for dm-qcow2 and dm-ploop
https://jira.vzint.dev/browse/PSBM-145746
Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>

---
v2: fix return and goto inconsistency
v3: normalize function assigments

 drivers/md/dm.c               | 41 +++++++++++++++++++++++++++++++++++
 include/linux/device-mapper.h |  4 ++++
 2 files changed, 45 insertions(+)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 7e5c61a75eeb..8bdfd0d4eb96 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -484,6 +484,45 @@ static int dm_blk_ioctl(struct block_device *bdev, fmode_t mode,
 	return r;
 }
 
+static loff_t dm_llseek_hole(struct block_device *bdev, loff_t offset, int whence)
+{
+	struct mapped_device *md = bdev->bd_disk->private_data;
+	struct dm_table *table;
+	struct dm_target *ti;
+	int srcu_idx;
+	loff_t ret;
+
+	table = dm_get_live_table(md, &srcu_idx);
+	if (!table || !dm_table_get_size(table))
+		return -ENOTTY;
+
+	/*
+	 * For now we only support devices that have a single target.
+	 * But probably it is not hard to break it to a few requests to a different
+	 * targets
+	 */
+	if (table->num_targets != 1)
+		return -EOPNOTSUPP;
+
+	ti = dm_table_get_target(table, 0);
+
+	if (dm_suspended_md(md)) {
+		ret = -EAGAIN;
+		goto out;
+	}
+
+	if (!ti->type->llseek_hole) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	ret = ti->type->llseek_hole(ti, offset, whence);
+
+out:
+	dm_put_live_table(md, srcu_idx);
+	return ret;
+}
+
 u64 dm_start_time_ns_from_clone(struct bio *bio)
 {
 	return jiffies_to_nsecs(clone_to_tio(bio)->io->start_time);
@@ -3255,6 +3294,7 @@ static const struct block_device_operations dm_blk_dops = {
 	.getgeo = dm_blk_getgeo,
 	.report_zones = dm_blk_report_zones,
 	.pr_ops = &dm_pr_ops,
+	.llseek_hole = dm_llseek_hole,
 	.owner = THIS_MODULE
 };
 
@@ -3264,6 +3304,7 @@ static const struct block_device_operations dm_rq_blk_dops = {
 	.ioctl = dm_blk_ioctl,
 	.getgeo = dm_blk_getgeo,
 	.pr_ops = &dm_pr_ops,
+	.llseek_hole = dm_llseek_hole,
 	.owner = THIS_MODULE
 };
 
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 0e1f72680533..ddca72a1fac2 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -152,6 +152,9 @@ typedef size_t (*dm_dax_copy_iter_fn)(struct dm_target *ti, pgoff_t pgoff,
 typedef int (*dm_dax_zero_page_range_fn)(struct dm_target *ti, pgoff_t pgoff,
 		size_t nr_pages);
 
+typedef loff_t (*dm_llseek_hole_fn)(struct dm_target *ti, loff_t offset,
+		int whence);
+
 void dm_error(const char *message);
 
 struct dm_dev {
@@ -203,6 +206,7 @@ struct target_type {
 	dm_dax_copy_iter_fn dax_copy_from_iter;
 	dm_dax_copy_iter_fn dax_copy_to_iter;
 	dm_dax_zero_page_range_fn dax_zero_page_range;
+	dm_llseek_hole_fn llseek_hole;
 
 	/* For internal device-mapper use. */
 	struct list_head list;
-- 
2.39.3