[PATCH RFC v2 1/2] block: scan partitions for hidden disks

[John Garry <john.g.garry@oracle.com>]

From: John Garry <john.garry@linux.dev>

If a disk is hidden (GENHD_FL_HIDDEN flags set), we currently do not scan
the disk partition table.

GENHD_FL_HIDDEN is used in NVMe multipath support to hide the per-path
disk.

However, it would be useful there to actually have the per-path disk
partition table available for situations where we want to send bios to
a specific per-path disk partition.

Change GENHD_FL_HIDDEN to scan partitions. For anyone wanting to avoid
scanning the partition, flag GENHD_FL_NO_PART can still be used.

In diskstats_show(), don't show per-path partitions as this info is not
too interesting and can just bloat the output.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 block/genhd.c            | 20 ++++++++++----------
 block/partitions/core.c  |  5 +++--
 drivers/nvme/host/core.c |  4 ----
 include/linux/blkdev.h   |  2 +-
 4 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 30ac0ffe65174..05301ee5d4ca5 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -406,15 +406,15 @@ static void add_disk_final(struct gendisk *disk)
 {
 	struct device *ddev = disk_to_dev(disk);
 
-	if (!(disk->flags & GENHD_FL_HIDDEN)) {
-		/* Make sure the first partition scan will be proceed */
-		if (get_capacity(disk) && disk_has_partscan(disk))
-			set_bit(GD_NEED_PART_SCAN, &disk->state);
+	/* Make sure the first partition scan will be proceed */
+	if (get_capacity(disk) && disk_has_partscan(disk))
+		set_bit(GD_NEED_PART_SCAN, &disk->state);
 
-		bdev_add(disk->part0, ddev->devt);
-		if (get_capacity(disk))
-			disk_scan_partitions(disk, BLK_OPEN_READ);
+	bdev_add(disk->part0, ddev->devt);
+	if (get_capacity(disk))
+		disk_scan_partitions(disk, BLK_OPEN_READ);
 
+	if (!(disk->flags & GENHD_FL_HIDDEN)) {
 		/*
 		 * Announce the disk and partitions after all partitions are
 		 * created. (for hidden disks uevents remain suppressed forever)
@@ -491,8 +491,7 @@ static int __add_disk(struct device *parent, struct gendisk *disk,
 	dev_set_name(ddev, "%s", disk->disk_name);
 	if (fwnode)
 		device_set_node(ddev, fwnode);
-	if (!(disk->flags & GENHD_FL_HIDDEN))
-		ddev->devt = MKDEV(disk->major, disk->first_minor);
+	ddev->devt = MKDEV(disk->major, disk->first_minor);
 	ret = device_add(ddev);
 	if (ret)
 		goto out_free_ext_minor;
@@ -1368,7 +1367,8 @@ static int diskstats_show(struct seq_file *seqf, void *v)
 
 	rcu_read_lock();
 	xa_for_each(&gp->part_tbl, idx, hd) {
-		if (bdev_is_partition(hd) && !bdev_nr_sectors(hd))
+		if (bdev_is_partition(hd) &&
+		    (!bdev_nr_sectors(hd) ||(gp->flags & GENHD_FL_HIDDEN)))
 			continue;
 
 		inflight = bdev_count_inflight(hd);
diff --git a/block/partitions/core.c b/block/partitions/core.c
index b5c59b79ca7cb..a48896c6c791d 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -152,7 +152,8 @@ static struct parsed_partitions *check_partition(struct gendisk *hd)
 
 	}
 	if (res > 0) {
-		printk(KERN_INFO "%s", seq_buf_str(&state->pp_buf));
+		if (!(hd->flags & GENHD_FL_HIDDEN))
+			printk(KERN_INFO "%s", seq_buf_str(&state->pp_buf));
 
 		kfree(state->pp_buf.buffer);
 		return state;
@@ -164,7 +165,7 @@ static struct parsed_partitions *check_partition(struct gendisk *hd)
 	 */
 	if (err)
 		res = err;
-	if (res) {
+	if (res && !(hd->flags & GENHD_FL_HIDDEN)) {
 		seq_buf_puts(&state->pp_buf,
 			     " unable to read partition table\n");
 		printk(KERN_INFO "%s", seq_buf_str(&state->pp_buf));
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 1322c678f4eb8..ed21f4ef36c9a 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1808,10 +1808,6 @@ static void nvme_enable_aen(struct nvme_ctrl *ctrl)
 
 static int nvme_ns_open(struct nvme_ns *ns)
 {
-
-	/* should never be called due to GENHD_FL_HIDDEN */
-	if (WARN_ON_ONCE(nvme_ns_head_multipath(ns->head)))
-		goto fail;
 	if (!nvme_get_ns(ns))
 		goto fail;
 	if (!try_module_get(ns->ctrl->ops->module))
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 9213a5716f95a..a270cf1394c7a 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -260,7 +260,7 @@ static inline unsigned int disk_openers(struct gendisk *disk)
  */
 static inline bool disk_has_partscan(struct gendisk *disk)
 {
-	return !(disk->flags & (GENHD_FL_NO_PART | GENHD_FL_HIDDEN)) &&
+	return !(disk->flags & GENHD_FL_NO_PART) &&
 		!test_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
 }
 
-- 
2.43.7